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Al x In 0.05− x Ta 0.05 Ti 0.9 O 2 ceramics with x ranging from 0 to 0.05 were synthesized using a conventional solid–state reaction method. All samples achieved a pure rutile–TiO 2 phase. Additionally, the lattice parameters of the samples increased with higher Al doping concentrations. The ceramics exhibited a dense microstructure and uniform dispersion of dopants. Raman spectroscopy revealed a decrease in oxygen vacancies in the structure with increasing Al3+ concentration. The presence of Ti3+ in the structure was confirmed by X–ray photoelectron spectroscopy. The dielectric properties of all samples were investigated as functions of frequency and temperature. The triple–doped AITTO ceramics demonstrated a high dielectric constant (ε′) of ∼2×104 and low dielectric loss (tanδ) ranging from 0.029 to 0.04, along with excellent temperature stability of ε′ at 1 kHz, showing a Δε′/ε′ 30 of less than ±15% over a temperature range of −60 to 210 °C. Notably, the tanδ of the triple–doped AITTO ceramics remained below 0.04 even at 200 °C. Impedance spectroscopy was utilized to analyze the electrical properties of the grains and grain boundaries. The observed dielectric properties are attributed to the formation of electron–pinned defect–dipoles, along with the impacts of both internal and surface barrier layer capacitors. [ABSTRACT FROM AUTHOR]

A modified sol−gel technique was used to synthesize a high dielectric ceramic, Na 1/3 Ca 1/3 Sm 1/3 Cu 3 Ti 4 O 12. The crystal structure of this sintered ceramic matches the standard pattern of a body−centered cubic (bcc) system within the Im3 space group (JCPDS No. 75–2188). No impurity phases were observed. Interestingly, a high dielectric permittivity of ∼1.14–1.35 × 104 and a low loss tangent of ∼0.027–0.039 were achieved in this sintered Na 1/3 Ca 1/3 Sm 1/3 Cu 3 Ti 4 O 12 ceramic. Our DFT calculations disclosed that substitution of Na+ ions at Cu2+ sites causes an observed excess Cu concentration. As a result, metastable insulating phases were formed at a relatively high sintering temperature. Additionally, our electron density calculations revealed that Na ions lose their electrons to Sm ions, whereas the oxidation states of Cu and Ti are unaltered. Our results show that Cu+ and Ti3+ were observed after introducing an oxygen vacancy into this lattice. Significantly different values of R g , R gb, and E g , E gb support an internal barrier layer capacitor as the most likely origin of the giant dielectric properties of this ceramic. XPS results show mixed Cu+/Cu2+ and Ti3+/Ti4+ in all ceramics, suggesting that electron hopping between Cu+↔Cu2+ and Ti3+↔Ti4+ is the probable origin of the n −type semiconducting state inside the grains. [ABSTRACT FROM AUTHOR]

The Sn x Ta 0.025 Ti 0.975- x O 2 (x %Sn(TTO)) ceramics with x = 2.5–10% were prepared using a standard mixed-oxide method and sintered at 1450 °C for 3 h to achieve a dense microstructure. The effects of the isovalent–Sn4+ doping concentration on the crystal structure, microstructure, giant dielectric behavior, and electrical properties were systematically investigated. Continuously enlarged lattice parameters and bond lengths with a single rutile–TiO 2 phase were observed as x % increased. The mean grain size was slightly reduced (∼17.3–14.6 μm) due to an increased oxygen vacancy and the solute drag effect. The dielectric permittivity (ε′) decreased with increasing x %, whereas the loss tangent (tanδ) was remarkably reduced. The semiconducting grain resistance of the x %Sn(TTO) ceramics remained unchanged owing to the same Ta5+ donor concentration. The insulating grain boundary (GB) resistance was extremely increased by more than two orders of magnitude when x % increased from 2.5 to 5.0%, leading to the significantly improved giant dielectric properties. The optimized low tanδ∼0.02 and high ε′∼104 with temperature coefficient less than ±15% in the range of -60–210 °C were reasonably described by the internal barrier layer capacitor model. Improved dielectric properties can be obtained by engineering GB by varying the Sn4+–isovalent doping concentration. This study provides an important approach for improving the dielectric properties of co–doped TiO 2 without the creation of complex defect clusters inside the grains. [ABSTRACT FROM AUTHOR]

Activated carbon (AC) from sugarcane bagasse was prepared using dry chemical activation with KOH. It was then subjected to a high-energy ball milling (HEBM) treatment under various milling speeds (600, 1200 and 1800 rpm) to produce AC nanoparticles from micro-size particles. The AC samples after the HEBM treatment exhibited reduced particle sizes, increased mesopore volume and a rich surface oxygen content, which contribute to higher pseudocapacitance. Notably, different HEBM speeds were used to find a good electrochemical performance. As a result, the AC/BM12 material, subjected to HEBM at 1200 rpm for 30 min, exhibited the highest specific capacitance, 257 F g−1, at a current density 0.5 A g−1. This is about 2.4 times higher than that of the AC sample. Moreover, the excellence capacitance retention of this sample was 93.5% after a 3000-cycle test at a current density of 5 A g−1. Remarkably, a coin cell electrode assembly was fabricated using the AC/BM12 material in a 1 M LiPF6 electrolyte. It exhibited a specific capacitance of 110 F g−1 with a high energy density of 27.9 W h kg−1. [ABSTRACT FROM AUTHOR]

Herein, NO2 noxious gas sensors based on precipitation/impregnation synthesized SnO2 nanoparticles loaded with Cu2O (Cu2O–SnO2) are presented. The particle properties are characterized by nitrogen adsorption, X‐ray spectroscopic, and microscopic analyses. The NO2‐sensing performances in terms of sensor response, response times, selectivity, and stability are optimized by varying Cu contents. The optimal sensing film (1.0 wt%Cu–SnO2) shows a high sensor response of ≈5680–5 ppm of NO2 at a low operating temperature of 200 °C. In addition, 1.0 wt%Cu–SnO2 sensor exhibits very high NO2 selectivity against SO2, H2S, C2H5OH, H2, C2H2, C2H4, and CH4 compared with unloaded one. Therefore, the 1.0 wt%Cu–SnO2 sensor is a promising candidate for highly sensitive and selective detection of NO2. [ABSTRACT FROM AUTHOR]

High-performance ceramics with chemical formula (Ni 1/3 Ta 2/3) x Ti 1−x O 2 with excellent dielectric properties are demonstrated. The dopants of Ni2+ and Ta5+ in TiO 2 caused the formation of oxygen vacancies and free electrons. The (Ni 1/3 Ta 2/3) x Ti 1−x O 2 exhibited low loss tangent of 0.046 and a high dielectric permittivity of 3.5–4.5 × 104 with a very weak dependence on temperature (−60 to 200 °C). Broadband dielectric spectroscopy shows at least four dominant sources in the dielectric relaxation response in the temperature range of − 253–210 °C. DFT calculations indicate the formation of defect clusters, which are the largest contributors to the dielectric response, and these are found to be dominant even at temperatures down to − 253 °C. Both grain boundary and surface layer mechanisms in the ceramics contribute to the dielectric response at the relatively high temperatures. The sample–electrode contact effect associated with oxygen vacancy diffusion is dominant at high temperatures above 150 °C. [ABSTRACT FROM AUTHOR]

Summary: This research aimed to improve the quality of waste tire pyrolysis oil (WTPO) via hydrogenation to eliminate polycyclic aromatic hydrocarbons (PAHs), which are classified as toxic compounds or precursors to induce the formation of particulate matter. Given the presence of organosulfurous compounds in WTPO, this research was consisted of two steps. First, the hydrogenation of naphthalene, a model PAH compound, was used to screen for suitable promoters [molybdenum (Mo), tungstate (W), and platinum (Pt)] for nickel‐supported gamma‐alumina (Ni/γ‐Al2O3) catalyst to provide a high sulfur tolerance and high PAH hydrogenation efficiency. Second, the obtained suitable catalysts were applied for the hydrogenation of 50 wt% WTPO solution in decane containing 15 982 ppm PAHs and a 0.75 wt% sulfur content. Although the NiPt/γ‐Al2O3 catalyst exhibited the highest performance with 83.8% naphthalene conversion under 40 bar initial H2 pressure at 350°C for 6 hours, it was less tolerant to the presence of thiophene, one of the organosulfurous compounds found in WTPO. Thus, the NiMo/γ‐Al2O3 and NiW/γ‐Al2O3 catalysts were selected for WTPO hydrogenation. The PAHs hydrogenation and hydrodesulfurization occurred simultaneously in both catalytic systems. Under 50 bar initial H2 pressure at 350°C, the NiMo/γ‐Al2O3 catalyst had a higher ability for hydrodesulfurization (98.4% maximum sulfur removal) than hydrogenation of PAHs (66.0% removal of PAHs), whereas NiW/γ‐Al2O3, with lower acidity, showed a preference for hydrogenation of PAHs (71.1% removal of PAHs) with a lower hydroisomerization efficiency (74.2% sulfur removal). Moreover, the chemical structure of PAHs affected the ability to be eliminated by hydrogenation. PAHs having unsubstituted rings could be easily hydrogenated, while the removal of PAHs containing alkyl substituents in both aromatic rings required severe reaction conditions due to their high steric hindrance for adsorption onto the catalyst active sites. [ABSTRACT FROM AUTHOR]

An acceptor-donor co-doped (Ga 1/2 Nb 1/2) 0.1 Ti 0.9 O 2 ceramic is triple-doped with Al3+, followed by sintering at 1450 °C for 5 h to obtain (Al x Ga 1/2- x Nb 1/2) 0.1 Ti 0.9 O 2 ceramics with improved giant dielectric properties. Homogeneous dispersion of all dopants inside the grains, along with the partially segregated dispersion of the Ga3+ dopant along the grain boundaries, is observed. The (Al x Ga 1/2- x Nb 1/2) 0.1 Ti 0.9 O 2 ceramics exhibit high dielectric permittivities (ε′∼4.2–5.1 × 104) and low loss tangents (tanδ∼0.007–0.010), as well as a low-temperature coefficients (<±15%) between − 60 and 200 °C. At 1 kHz, tanδ is significantly reduced by ∼4.4 times, while ε′ is increased by ∼3.5 times, which is attributed to the higher Al3+/Ga3+ ratio. The value of tanδ at 200 °C is as low as 0.04. The significantly improved dielectric properties are explained based on internal and surface barrier-layer capacitor effects, which are primarily produced by the Ga3+ and Al3+ dopants, respectively, whereas the semiconducting grains are attributed to Nb5+ doping ions. [ABSTRACT FROM AUTHOR]

Various strategies to improve the dielectric properties of ACu3Ti4O12 (A = Sr, Ca, Ba, Cd, and Na1/2Bi1/2) ceramics have widely been investigated. However, the reduction in the loss tangent (tanδ) is usually accompanied by the decreased dielectric permittivity (ε′), or vice versa. Herein, we report a route to considerably increase ε′ with a simultaneous reduction in tanδ in Ta5+–doped Na1/2Y1/2Cu3Ti4O12 (NYCTO) ceramics. Dense microstructures with segregation of Cu– and Ta–rich phases along the grain boundaries (GBs) and slightly increased mean grain size were observed. The samples prepared via solid‐state reaction displayed an increase in ε′ by more than a factor of 3, whereas tanδ was significantly reduced by an order of magnitude. The GB–conduction activation energy and resistance raised due to the segregation of Cu/Ta–rich phases along the GBs, resulting in a decreased tanδ. Concurrently, the grain–conduction activation energy and grain resistance of the NYCTO ceramics were reduced by Ta5+ doping ions owing to the increased Cu+/Cu2+, Cu3+/Cu2+, and Ti3+/Ti4+ ratios, resulting in enhanced interfacial polarization and ε′. The effects of Ta5+ dopant on the giant dielectric response and electrical properties of the grain and GBs were described based on the Maxwell–Wagner polarization at the insulating GB interface, following the internal barrier layer capacitor model. [ABSTRACT FROM AUTHOR]

CaCu 3-x Zn x Ti 4 O 12 ceramics (x = 0, 0.05, 0.10) were successfully prepared by a conventional solid-state reaction method. Their structural and dielectric properties, and nonlinear electrical response were systematically inspected. The X-ray diffraction results indicated that single-phase CaCu 3 Ti 4 O 12 (JCPDS no. 75–2188) was obtained in all sintered ceramics. Changes in the lattice parameter are well-matched with the computational result, indicating an occupation of Zn2+ doping ions at Cu2+ sites. The overall tendency shows that the average grain size decreases when x increases. Due to a decrease in overall grain size, the dielectric permittivity of CaCu 3-x Zn x Ti 4 O 12 decreases expressively. Despite a decrease in the dielectric permittivity, it remains at a high level in the doped ceramics (~3,406–11,441). Besides retention in high dielectric permittivity, the dielectric loss tangent of x = 0.05 and 0.10 (~0.074–0.076) is lower than that of x = 0 (~0.227). A reduction in the dielectric loss tangent in the CaCu 3-x Zn x Ti 4 O 12 ceramics is closely associated with the enhanced grain boundary response. Increases in grain boundary resistance, breakdown electric field, and conduction activation energy of grain boundary as a result of Zn2+ substitution are shown to play a crucial role in improved grain boundary response. Furthermore, the XPS analysis shows the existence of Cu+/Cu2+ and Ti3+/Ti4+, indicating charge compensation due to the loss of oxygen lattice. Based on all results of this work, enhanced dielectric properties of the Zn-doped CCTO can be explained using the internal barrier layer capacitor model. [ABSTRACT FROM AUTHOR]

CaCu 3 Ti 4 O 12 ceramics have been extensively studied for their potential applications as capacitors in recent years; however, these materials exhibit very large dielectric losses. A novel approach to reducing the dielectric loss tangent in two steps, while increasing the dielectric permittivity, is presented herein. Doping CaCu 3 Ti 4 O 12 with a Zn dopant reduces the loss tangent of the ceramic material from 0.227 to 0.074, which is due to the increase in grain boundary (GB) resistance by an order of magnitude (from 6.3× 103 to 3.93 × 104 Ω cm). Zn-doping slightly changes the microstructure and dielectric permittivity of the CaCu 3 Ti 4 O 12 ceramic, which reveals that the primary role of the Zn dopant is to tune the intrinsic properties of the GBs. Surprisingly, the addition of the Ge4+ dopant into the Zn2+-doped CaCu 3 Ti 4 O 12 ceramic sample led to a further decrease in the loss tangent from 0.074 to 0.014, due to enhanced GB resistance (3.1 × 105 Ω cm). The grain size increased remarkably from 2–3 μm to 85–90 μm, corresponding to a significant increase in the dielectric permittivity (~1–4 × 104). The large increase in GB resistance is due to the intrinsic potential barrier height at the GBs and the segregation of the Cu-rich phase in the GB region. First-principles calculations revealed that Zn and Ge are preferentially located at the Cu sites in the CaCu 3 Ti 4 O 12 structure. The substitution of the Ge dopant does not hinder the role of the Zn dopant in terms of improving the electrical properties at the GBs. These phenomena are effectively explained by the internal barrier layer capacitor model. This study provides a way of improving the dielectric properties of ceramics for their practical use as capacitors. [ABSTRACT FROM AUTHOR]

Nanocrystalline powders of BiFe 1- x Mg x O 3 (x = 0, 0.05, and 0.10) were prepared via a co−precipitation method. This produced a dense ceramic microstructure when sintering the compacted nanocrystalline powders at 800 °C for 3 h. A main phase of BiFeO 3 with a small number of impurity phases was confirmed to exist in the sintered ceramics. High ε′ values of 103-105 in the temperature range of 200–473 K were obtained. Dielectric relaxation behavior was studied over a wide temperature range. The low− and high−temperature dielectric relaxations originated from electron hopping between Fe2+↔Fe3+ and the interfacial polarization associated with the long−range motion of free charge carriers, respectively. To describe the dielectric properties of the Mg2+−doped BiFeO 3 ceramics, theoretical calculations were performed to investigate the most preferable formation of complex defects. It was found that the dopant concentration had an effect on the defect shapes and dielectric properties. [ABSTRACT FROM AUTHOR]

Microstructure, dielectric, and electrical properties of CaCu3−xGexTi4O12 ceramics with x = 0–0.10 prepared by a conventional solid-state reaction method are investigated. Single-phase of CaCu3Ti4O12 was detected in all sintered ceramics. The substitution of Ge4+ into Cu2+ sites results in the grain size of CaCu3−xGexTi4O12 ceramics to decrease, compared to CaCu3Ti4O12 ceramic. Unusually, although grain sizes of CaCu3−xGexTi4O12 ceramics decrease, their dielectric permittivity is increased by doping. Enhanced dielectric permittivity ~ 35,000–42,000 with reduced loss tangent ~ 0.037–0.053 was achieved in x = 0.025–0.10. Improved dielectric properties with reduced loss tangent might be originated by enhanced grain boundary response, especially the largely increased grain boundary resistance. The result obtained from an impedance spectroscopy technique indicates the formation of an internal barrier layer capacitor model in all sintered ceramics. The giant dielectric permittivity of CaCu3−xGexTi4O12 ceramics might be caused by intrinsically compensating mechanisms of charge carriers. [ABSTRACT FROM AUTHOR]

Poly(vinylidene fluoride) (PVDF)-based nanocomposites were fabricated using a hybrid combination of Au nanoparticles (AuNPs) and BiFeO 3 (BFO) NPs as a filler. AuNPs with sizes of 10–20 nm were deposited onto the surface of the BFO NPs via a modified Turkevich 's method to obtain Au–BFO hybrid NPs. α -, β -, and γ -PVDF phases were detected in all the polymer nanocomposites. The fraction of the electroactive (i.e. polar) β -phase of the PVDF polymer increased after the incorporation of the hybrid NPs. The AuNPs and BFO NPs were homogeneously dispersed in the PVDF matrix. PVDF filled with the Au–BFO hybrid NPs showed a significantly increased dielectric permittivity—which was 5 times that of pure PVDF polymer—whereas the conductivity and corresponding loss tangent of all the nanocomposites remained lower than 0.05 at room temperature and 1 kHz. The enhanced permittivity was primarily a result of the strong interfacial polarisation and partly a result of the high permittivity of the BFO NPs and the formation of the β -PVDF phase. The suppressed loss tangent was attributed to the discrete growth of AuNPs on the surface of the BFO NPs, which inhibited the formation of the conduction pathway in the PVDF matrix. [ABSTRACT FROM AUTHOR]

Selective CO2 hydrogenation to light olefins over Fe−Co/K−Al2O3 catalysts was enhanced by tuning bonding strengths of adsorbed species by varying the content of the K promotor. Increasing the K/Fe atomic ratio from 0 to 0.5 increased the olefins/paraffins (O/P) ratio by 25.4 times, but then slightly raised upon ascending K/Fe to 2.5. The positive effect of K addition is attributed to the strong interaction of H adsorbed with the catalyst surface caused by the electron donor from K to Fe species. Although the Fe−Co/K−Al2O3 catalyst with K/Fe=2.5 reached the highest O/P ratio of 7.6, the maximum yield of light olefins of 16.4 % was achieved by the catalyst promoted with K/Fe of 0.5. This is explained by the considerable reduction of amount of H2 adsorbed on the catalyst surface with K/Fe=2.5. [ABSTRACT FROM AUTHOR]

Giant dielectric behavior and electrical properties of monovalent cation/anion (Li+, F−) co‐doped CaCu3Ti4O12 ceramics prepared by a solid‐state reaction route were systematically investigated. Substitution of Li+ and F− led to a significantly enlarged mean grain size. A reduced loss tangent (tanδ ~0.06) with the retainment of an ultra‐high dielectric permittivity (ε′ ~7.7‐8.8 × 104) was achieved in the co‐doped ceramics, while the breakdown electric field and nonlinear coefficient of CaCu3Ti4O12 ceramics were increased by co‐doping with (Li+, F−). The variations in nonlinear electrical properties and giant dielectric response, as well as the dielectric relaxation, were well explained by the Maxwell‐Wagner polarization model for an electrically heterogeneous microstructure, in which a Schottky barrier height at the grain boundaries (GBs) was formed. ε′ was closely correlated to the GB capacitance. Significantly decreased tanδ value and enhanced nonlinear properties were related to a significant increase in the GB resistance, which was attributed to the significantly increased potential barrier height and conduction activation energy at the GBs. The semiconducting nature of the grains was also studied using X‐ray photoelectron spectroscopy and found to originate from the presence of Cu+ and Ti3+ ions. [ABSTRACT FROM AUTHOR]

• Simple sonication can lead to strong decrease in graphene oxide(GO) sorption capacity. • Observed across all test species: elemental cation, cationic, anionic dye molecules. • Sonication causes GO's various oxygen groups to be removed with increased C/O ratios. • Increased defects on sonicated GO's basal plane also decrease π-π attractions. • Mechanism based on radicals generated from sonication react with GO's facile oxygen proposed. A sonochemical approach is widely used as a routine protocol for graphene oxide (GO) preparation prior to adsorption applications, but there is a limited understanding of its effects on the GO sorption ability. Herein, using different types of sorbates, which are cation, cationic and anionic dye, the changes in sorption capacity along with the characteristics of sonicated GO, are shown. The ultrasound treatment unexpectedly removes oxygen functional groups from GO with a concomitant decrease in GO adsorption capacity, rather than an increase in its adsorption as expected from the use of ultrasound in dispersing or exfoliating GO. The C/O ratio increases from 2.1 in pristine GO up to 2.5 in sonicated GO. The loss of oxygen functional groups is also accompanied by an increase in disorder and defects on GO sheets, along with the weakening of π-π interaction. The pathways of GO's structural and functional groups changed by ultrasound are proposed, based on the generation of OH· radicals from ultrasonic cavitation. These radicals can react with the facile oxygenated groups of GO, such as those of epoxide, hydroxyl, and carboxyl, leading to the partial removal of these groups and the breakage of GO sheets. GO's adsorption capacities for cation and different dyes can decrease up to 75% after sonication, which is in agreement with the above changes in GO's characteristics. The effects are readily observed even in mild sonication such as using an ultrasonic bath, signifying their importance in many applications employing ultrasonication to disperse GO. [ABSTRACT FROM AUTHOR]

Light olefins can be produced from CO 2 hydrogenation in a single reactor using a combination of a methanol synthesis catalyst and a methanol-to-olefin (MTO) catalyst. However, commercial methanol synthesis catalysts are active at low temperatures (200–260 °C), while MTO reaction is feasible at higher temperatures (>300 °C). Herein, we report the CO 2 hydrogenation to methanol at high temperatures (320–400 °C) over Ga x In 2−x O 3 catalysts. By tuning the Ga/In ratios, phase, crystallinity, pore structure, morphology, electronic properties as well as adsorptive properties of Ga x In 2−x O 3 catalysts can be modified. At the lowest temperature (320 °C), the pure In 2 O 3 shows the highest methanol yield. However, the maximum methanol yield declines significantly with increasing reaction temperatures. Incorporation of Ga into the In 2 O 3 crystal lattices at x = 0.4 (Ga 0.4 In 1.6 O 3) maximizes the methanol yield at higher reaction temperatures of 340–360 °C. This enhancement can be attributed to an increased binding energy of adsorptive molecules with the catalyst surface to promote the hydrogenation of CO 2 to methanol. Further increasing Ga content (x > 0.4) leads to greatly strengthen the binding for adsorptive molecules, resulting in a lower methanol yield and the formation of methane. The surface chemisorbed oxygen is found to be a key factor determining the CO yield. Unlabelled Image • Pure In 2 O 3 showed the maximum CH 3 OH yield at 320 °C. • Electronic properties of pure In 2 O 3 were perturbed when incorporated with Ga. • At 340–360 °C, the maximum CH 3 OH yield achieved over Ga 0.4 In 1.6 O 3 • Increasing Ga content to x = 0.9 exhibited the highest CH 4 yield. • Pure Ga 2 O 3 showed the maximum DME yield at all reaction temperatures. [ABSTRACT FROM AUTHOR]

Abstract The aim of this work was to prepare the metal oxides modified carbon (C-MO x) that was used as the support for a PtCo catalyst. Effect of C-MO x support on the oxygen reduction reaction activity and stability of the PtCo catalysts in acid electrolyte and in proton exchange membrane fuel cell was explored at ambient pressure. It was found that the use of respective C-MO x support changed the morphologies (degree of alloying and particle sizes) as well as the electrochemical properties (electrode resistance and electrochemical surface area) of the obtained PtCo catalyst. In addition, it enhanced the formation of Pt atoms with a small d -electron occupancy, which consequently affected positively the ORR activity of the PtCo catalysts. Among the three utilized C-MO x support (C-TiO x , C-CeO x , C-MoO x), the C-MoO x exhibited the highest ORR activity in an acid electrolyte monitored in terms of kinetic current density and the highest current density of 570 mA/cm2 at 60 °C and 1 atm (abs) in a proton exchange membrane (PEM) fuel cell. In addition, it also achieved a comparable stability of PtCo catalyst to that of C-TiO x support, which were higher than that of the commercial carbon support. Highlights • Effect of C-MO x support on the ORR activity and stability of PtCo catalysts was explored at ambient pressure. • Respective C-MO x support changed the morphology and electrochemical property of PtCo catalyst. • The C-MO x support enhanced the formation of Pt atoms with small d -electron occupancy. • The C-MoO x resulted in the highest ORR activity and stability of PtCo catalyst. • The PtCo/C-Mo x catalyst was recommended for use as cathode catalyst in PEM fuel cell. [ABSTRACT FROM AUTHOR]

In this work, the hydrogenation of CO 2 to light olefins has been studied over the Fe-Co/K-Al 2 O 3 catalysts, while focusing on the impact by the pore sizes of Al 2 O 3 supports including 6.2 nm (S-Al 2 O 3), 49.7 nm (M-Al 2 O 3) and 152.3 nm (L-Al 2 O 3) on the structure and catalytic performance. The characterization results demonstrate that the pore sizes of the Al 2 O 3 supports play a vital role on the crystallite size of Fe 2 O 3 , the reducibility of Fe 2 O 3 and the adsorption-desorption of CO 2 and H 2. The catalyst with the smallest pore size (CS-Al 2 O 3) allows the formation of a small Fe 2 O 3 crystallite size due to pore confinement effects, yielding a low active component (Fe) after reduction at 400 °C for 5 h. The catalysts with the larger pore sizes of 49.7 nm (CM-Al 2 O 3) and 152.3 nm (CL-Al 2 O 3) provide the larger Fe 2 O 3 crystallite sizes which require a longer reduction time for enhancing degree of reduction, resulting in a high metallic Fe content, leading to a high CO 2 conversion and a high selectivity toward hydrocarbon. Eliminating diffusion limitation by increasing the pore sizes of Al 2 O 3 supports can suppress the hydrogenation of olefins to paraffins and thus the largest pore catalyst (CL-Al 2 O 3) gives the highest olefins to paraffins ratio of 6.82. Nevertheless, the CL-Al 2 O 3 also favors the formation of C 5+ hydrocarbon. Therefore, the highest light olefins yield (14.38%) is achieved over the catalyst with appropriated pore size (CM-Al 2 O 3). Unlabelled Image • Increasing pore size enlarges Fe 2 O 3 crystallite size and facilitates its reducibility. • Hydrocarbon selectivity is correlated to Fe contents. • Increasing pore size promotes the formation of long chain hydrocarbons. • The maximum light olefins yield achieves over the catalyst with pore size of 49.7 nm. [ABSTRACT FROM AUTHOR]

Nitrogen- and co-nitrogen- and sulfur-doped reduced graphene oxide (named N-rGO and N/S-rGO) was prepared by a simple hydrothermal technique using urea and thiourea as doping agents, respectively, to improve the properties of supercapacitor electrodes. Both were compared with rGO in electrochemical evaluations. The supercapacitor using N-rGO in 1 M H 2 SO 4 provided the largest specific capacitance, 99 F g−1, while those using N/S-rGO and rGO exhibited 51 and 19 F g−1 at 0.25 A g−1, respectively. Furthermore, the supercapacitors using N-rGO and N/S-rGO electrodes showed a smaller charge transfer resistance (R ct) and a lower IR -drop than those using the rGO electrode, indicating a faster charge transfer at the interface between electrode and electrolyte and higher electronic conductivity due to N or N/S heteroatom doping in the graphene oxide structure. Furthermore, the N-rGO electrode has a higher sp2 hybridization ratio and a lower I D /I G ratio than the N/S-rGO electrode. Furthermore, the lowest contact angles of the N/S-rGO electrode were found, which was attributed to better aqueous electrolyte compatibility than the N-rGO and rGO electrodes. Therefore, the higher electrical conductivity of the N-rGO electrode reveals more relevant characteristics for high-performance supercapacitors than the good wettability of the N/S-rGO electrode. • N- and N/S-doping rGO can improve the conductivity and wettability of electrodes. • N- and N/S-doped rGO demonstrates a reduction in the sp2 hybridization ratio and an increase in I D /I G. • The specific capacitance of N-rGO is greater than that of N/S-rGO and rGO. • The cycle stability of N-rGO is superior to that of N/S-rGO and rGO. [ABSTRACT FROM AUTHOR]

Abstract In this work, x Al 2 O 3 -(1 − x)CaCu 3 Ti 4 O 12 , where x = 0, 2, and 10 vol%, nanocomposites were prepared by a conventional mixed oxide method using Al 2 O 3 nanopowders with particle sizes of ≈20–40 nm. The giant dielectric properties, electrical responses and nonlinear characteristics of Al 2 O 3 -CaCu 3 Ti 4 O 12 nanocomposites were investigated. Interestingly, the (2 vol%)Al 2 O 3 -CaCu 3 Ti 4 O 12 ceramic exhibited significantly improved dielectric properties with large dielectric constant and low loss tangent values of about of 2.0 × 104 and 0.038, respectively. The nonlinear current-voltage properties of CaCu 3 Ti 4 O 12 ceramics were also enhanced by the addition of Al 2 O 3. X-ray photoelectron spectroscopy technique was used to confirm the existence of Cu+, Cu3+ and Ti3+ ions in the composite ceramics, indicating the primary cause of the conduction mechanism inside the grains. The first principle calculation was performed to predict the most possibility of site preference of Al ion in CCTO lattice structure. The improved dielectric and nonlinear electrical properties can be well explained based on the internal barrier layer capacitor effect, resulting from the improved electrical properties of internal interfaces. Graphical abstract x Al 2 O 3 -(1 − x)CaCu 3 Ti 4 O 12 , where x = 0, 2, and 10 vol%, nanocomposites are prepared by a conventional mixed oxide method using Al 2 O 3 nanopowders with particles sizes of ≈20–40 nm. The presence of Cu+, Cu3+, and Ti3+ ions are detected in the composite ceramics confirmed by X-ray photoelectron spectroscopy (XPS) technique. Low tanδ ≈ 0.038 and high ε′ ≈ 2.0 × 104 at 1 kHz are achieved. Unlabelled Image Highlights • x Al 2 O 3 -(1 − x)CaCu 3 Ti 4 O 12 nanocomposites using Al 2 O 3 nanopowders (≈20–40 nm) • tanδ ≈ 0.038 and ε′ ≈ 2.0 × 104 with Δε′ < ±15% in the range of −60–90 °C were achieved. • Cu+, Cu3+, and Ti3+ ions were confirmed by XPS technique. [ABSTRACT FROM AUTHOR]

CeCuO x nanocatalysts with different Ce/Cu ratios from 10 to 40 at% Cu loading were systematically prepared by a simple and environmental-friendly method using cetyltrimethylammonium bromide (CTAB) as a template. The stabilized ion pairs between cationic CTAB and the mix metal salts facilitated nucleation and growth of the nanoparticles resulted in narrow size distribution. XPS results indicated the presence of Cu species (Cu 2+ or metallic Cu 0 ) in CeCuO x catalysts. Compared with CeO 2 , the CeCuO x catalysts provided the lower hydrogen reduction temperature. The Ce 0.8 Cu 0.2 O x showed the highest toluene conversion which could be due to the high surface area and well dispersion of the Cu species in the CeO 2 matrix. [ABSTRACT FROM AUTHOR]

Hexagonal nanoplates of Ni(OH) 2 with a thickness of ∼11 nm were synthesized by a simple hydrothermal method. The formation of Ni(OH) 2 phase was confirmed by XRD technique. TEM images revealed a stack of hexagonal nanosheets with average nanoplates size of ∼62 nm. XPS results confirm the elemental compositions at the surface of Ni(OH) 2 which are in good agreement with XRD results. As we know, the properties of electrolyte affect the performance of supercapacitors. Therefore, the electrochemical performance of Ni(OH) 2 electrodes were investigated in various aqueous electrolyte solutions including 1M NaOH, 2M KOH, and 1M KOH mixed with 0.5M Na 2 SO 4 . The electrochemical results show that the Ni(OH) 2 electrode in 1M NaOH electrolyte reached the highest specific capacitance of 447 F/g at a current density of 1 A/g that was nearly two times higher than that in the 2M KOH electrolyte. This can be attributed to the smaller ionic radius of the Na + ion and a higher intercalation/deintercalation rate of Na + ions into the surface of the Ni(OH) 2 electrode. In addition, a coulombic efficiency of 94% was found in 1M NaOH at a current density of 10 A/g. The capacitance retention of the Ni(OH) 2 electrode in 1M NaOH was maintained at about 100% after 1000 cycles. The present work proves that the best performance of Ni(OH) 2 nanoplates was performed in the 1M NaOH electrolyte. [ABSTRACT FROM AUTHOR]

The dielectric properties of poly(vinylidene fluoride) (PVDF) polymer incorporating with silver (Ag) nanoparticles, which were successfully prepared via a hydrothermal method using Aloe vera plant–extracted solution as surface stabilizer and reducing agent (Ag@Ale–NPs), were investigated. Ag@Ale–NPs/PVDF polymer nanocomposites were prepared by a liquid–phase assisted dispersion and hot–pressing methods. The microstructures of the Ag@Ale–NPs and Ag@Ale–NPs/PVDF nanocomposites were characterized. The modification of the Ag@Ale–NPs surface was confirmed using X–ray photoelectron spectroscopy. Interestingly, by using a filler volume fraction of 0.18, the composite exhibited a high dielectric permittivity of ≈92.5 with very low loss tangent of 0.049 at room temperature and 1 kHz. With further increasing a filler volume fraction to 0.22, a greatly enhanced dielectric permittivity of ≈257.2 was obtained with low loss tangent (tan δ ≈ 0.26). Excellent dielectric properties of the Ag@Ale–NPs/PVDF nanocomposites were described by the interfacial polarization effect and the formation of micro–capacitor in the PVDF polymer matrix. [ABSTRACT FROM AUTHOR]

Pd-based catalysts supported on high-surface-area carbon are widely used in formic acid fuel cells. The composition, structure, and support can be modified to maximize the capabilities of Pd-based catalysts in terms of catalytic activity, durability, and cost. Various studies have investigated tuning the properties of Pd-based catalysts by alloying Pd with other metals. In this study, Cr, Ni, Cu, and Zn were incorporated into Pd-based catalysts. First, the effects of mole ratios were studied between Pd and the metals. The PdnNi ratios on a reduced graphene oxide support (PdnNi/rGO) were prepared using the one-pot method without the use of any surfactants. All obtained rGO-supported PdnNi catalysts (n = 1, 2, 4, with diameter of 5 nm) were used for the electrocatalytic oxidation of formic acid. The electro-oxidation measurements revealed that the PdnNi/rGO samples had superior electrocatalytic performance both in current densities and stabilities for formic acid oxidation (FAO) compared to Pd/rGO. Furthermore, Pd4Ni/rGO had greater electrocatalytic activity than the other PdnNi/rGO samples. In addition, with the same mole ratio of metals, Pd4Cr/rGO had higher efficiency toward FAO than the other series in the order: Pd4Cr/rGO > Pd4Ni/rGO > Pd4Cu/rGO > Pd4Zn/rGO. [ABSTRACT FROM AUTHOR]

Giant dielectric properties (GDPs) of complex oxides have been widely investigated because of their potential applications in ceramic capacitors. This study describes the improvement in three crucial factors of the GDPs of TiO 2 by co-doping it with Tb and Nb ions. (Tb 0.5 Nb 0.5) x Ti 1- x O 2 (TNTO) ceramics with x = 1–5% were prepared using a conventional mixed-oxide method. The ceramics exhibited a highly compact microstructure and microwave dielectric phases of Tb 2 Ti 2 O 7 and TbNbTiO 6. Notably, the temperature dependence of the dielectric permittivity (ε′) (∆ ε ′ (T) / ε ′ 30 ℃ ) was less than | ± 15%| from − 60–210 ℃. Furthermore, the TNTO ceramics exhibited extremely low tanδ values (0.006–0.011) and high ε′ values (4.7–5.3 ×104) at 1 kHz. The tanδ values at 200 °C were particularly low (0.033–0.057). Impedance spectroscopy revealed the presence of semiconducting grains, and the enormous resistivity of the grain boundaries and microwave dielectric phase particles. The GDPs are primarily caused by both intrinsic and extrinsic effects. The intrinsic effect was due to the formation of defect clusters (i.e., Nb 2 5 + Ti 3 + X Ti (X = A 3 + / Ti 3 + / Ti 4 +) − Tb 2 3 + V 0 • • Ti 3 + , 2 Tb Ti ′ − V O • • , Tb Ti ′ − Nb Ti • , 3 Ti Ti ′ − V O • • − Nb Ti • , and Ti Ti ′ − V O • • − Ti Ti ′ ), whereas the extrinsic effect resulted from the internal barrier layer capacitor microstructure. The presence of microwave dielectric phases can cause a decrease in tanδ and improve the temperature stability of ε′. • GDPs of TiO 2 can be improved by co-doping it with Tb and Nb ions. • TiO 2 -based ceramics exhibit ultra-low tan δ values and high ε′ values at 1 kHz. • GDPs of TiO 2 -based ceramics arise due to both intrinsic and extrinsic effects. • Microwave dielectric phases in TiO 2 -based ceramics can decrease tan δ. [ABSTRACT FROM AUTHOR]

To increase the ethanol sensing at low operating temperatures in ZnO nanostructure sensors, the gold nanoparticles were introduced to ZnO nanostructures (ZnO:AuNPs) by a sputtering technique. Then, the ethanol sensing characteristics were investigated under UV illumination at the temperatures in the range of 25–125 °C. It was found that the sensor response of ZnO:AuNPs sensor under UV illumination was remarkably improved. Moreover, the sensor based on ZnO:AuNPs under UV illumination exhibited the increasing of sensor response toward ethanol vapor with an increasing of UV illumination intensity from 0 to 4.1 mW/cm 2 . The sensor response enhancement mechanism can be explained by two main effects including sensor response enhancement due to an addition of AuNPs on ZnO nanostructures and UV illumination. The AuNPs added onto ZnO nanostructure strongly affect the chemical reaction change in the oxygen adsorption reaction resulting in a larger depletion layer width. As a result, the sensor response is enhanced to higher than that of ZnO nanostructure sensor. The sensor response enhancement due to UV illumination is explained by the formation of weakly bound oxygen ions from electron carriers being excited from band to band and oxygen molecule in air. This produces a thinner depletion layer width with the weakly bound oxygen ions due to the photo activation which are easily removed from the ZnO surface resulting in high sensor response with lower resistance. [ABSTRACT FROM AUTHOR]

High-performance giant dielectric properties (HP-GDPs) of acceptor–donor co-doped TiO 2 are generally based on effective suppression of the loss tangent (tanδ) and significant enhancement of dielectric permittivity (ε′). In this study, a solid state reaction was used to prepare TiO 2 -based ceramics displaying HP-GDPs by co-doping with isovalent SnO 2 and Nb 2 O 5 as a donor at different concentrations. The sintered ceramics showed a dense microstructure (>97 %) and well-dispersed dopants. The grain size slightly increased (from 1.6 to 2.6 µm) when the co-doping concentration increased from 1 % to 5 %. The ceramic with the optimal composition featured a large ε′ = 3.0 × 104 and a small tanδ = 0.012. Furthermore, the small change in its ε′ value (by less than±15 % between −55 and 150 °C) meets the temperature dependence requirement for application in the X8R capacitor. The HP-GDPs observed here were primarily caused by Maxwell-Wagner polarization at the internal interface with a large resistivity between the semiconducting grains. • Dense microstructure of isovalent SnO 2 and Nb 2 O 5 codoped TiO 2 was obtained. • Large ε′ ∼ 3.0 × 104 and low tanδ ∼ 0.012 were accomplished. • Small change in ε′ by less than± 15 % between −55 and 150 °C was obtained. • Dielectric properties were primarily caused by Maxwell–Wagner polarization. [ABSTRACT FROM AUTHOR]

• SnTTO ceramic exhibited a high ε′ value of 44,112 and a low tanδ value of 0.011. • Δε′(%) was less than 15% in the temperature range of −60 – 170 °C. • Dielectric behavior can be well described by the IBLC model. • Roles of Ta5+ and Sn4+ were to create free charges and increase R gb , respectively. The excellent dielectric performance of an Sn4+–isovalent/Ta5+–pentavalent doped TiO 2 (SnTTO) ceramic was investigated. Substitution of Sn4+ into TiO 2 caused slight changes in the dielectric permittivity (ε′) and loss tangent (tanδ). Although doping TiO 2 with Ta5+ can cause a substantial increase in ε′, tanδ was very large. Notably, the SnTTO ceramic exhibited a high ε′ value of 44,112 and a low tanδ value of 0.011 at 1 kHz and 25 °C. Furthermore, the temperature coefficient of ε′ (Δε′(%)) was less than 15% in the temperature range of −60–170 °C. The microstructure of the codoped SnTTO consisted of semiconducting grains and grain boundaries (GBs) with very large GB resistance (R gb) value, thereby leading to effective retention of a low tanδ value and a small Δε′(%) value. Evidently, the primary roles of the Ta5+ and Sn4+ doping ions were to increase the interfacial polarization via increased free charges and increased R gb by reducing the oxygen vacancies at the GBs. [Display omitted] [ABSTRACT FROM AUTHOR]

• Very high ε′ of CaCu 3- x Mg x Ti 4 O 12 ranging from 6.58 × 103 to 2.87 × 104 was observed. • Low loss tangents of ∼0.011 − 0.025 were obtained in these ceramics. • ε′ of CaCu 2.90 Mg 0.10 Ti 4 O 12 is stable over temperature range from −60 to 120 °C. • Vo was likely to be isolated from the Mg atoms in the CaCu 3- x Mg x Ti 4 O 12. • Colossal dielectric properties support the internal barrier layer capacitor model. In this work, CaCu 3- x Mg x Ti 4 O 12 (x = 0, 0.05, and 0.10) ceramics were successfully prepared via a chemical combustion method. No impurity phase was detected in these two ceramics. Fine−grained microstructures were formed in all CaCu 3- x Mg x Ti 4 O 12 ceramics. Interestingly, high dielectric permittivities of ∼6.58 × 103 − 2.87 × 104 with low loss tangents of ∼0.011 − 0.025 were obtained in the Mg-doped CaCu 3 Ti 4 O 12 ceramics. According to the electrical measurements, improved dielectric properties in the doped ceramic samples were a result of an enhanced grain boundary response. To elucidate the electronic structure of CaCu 2.90 Mg 0.10 Ti 4 O 12 , first-principles calculations were carried out. It was found that two Mg atoms preferentially interact. Moreover, by adding an oxygen vacancy into the CaCu 2.90 Mg 0.10 Ti 4 O 12 structure, our results revealed that it was likely to be isolated from the Mg atoms, indicating an oxygen loss suppression during the sintering process. This resulted in an enhanced grain boundary resistance in the CaCu 2.90 Mg 0.10 Ti 4 O 12 ceramic. Based on both the experimental and computational studies, the internal barrier layer capacitor (IBLC) model was found to be the primary origin of the colossal dielectric response in all CaCu 3- x Mg x Ti 4 O 12 ceramics examined in the current study. Graphical Abstract [Display omitted]. [ABSTRACT FROM AUTHOR]

Lithium cobalt oxide (LiCoO 2) powder was prepared by co-precipitation method and annealed at different temperatures of between 300 and 700 °C. The effect of annealing temperature and effect washing process with deionized water on the crystal structures of the prepared LiCoO 2 powders were thoroughly studied by Synchrotron powder X-Ray Diffraction (Syn-XRD), X-ray Absorption Spectroscopy (XAS), Dispersive Raman Microscopy (Raman) techniques. The change in chemical composition as a function of annealing temperature was also investigated by X-ray Photoelectron Spectroscopy (XPS) technique. The crystal structural results identified the phase evolution of the prepared LiCoO 2 powders upon heat treatment. The formation of HT-LiCoO 2 phase was observed at annealing temperature as low as 300 °C. • Structure of LiCoO2 powder was studied by Synchrotron XRD and XAS techniques. • Formation of HT-LiCoO2 phase was observed at annealing temperature of 300 °C. • Washing process affects surface chemical composition of LiCoO2 powder. [ABSTRACT FROM AUTHOR]

Giant dielectric (GD) oxides exhibiting extremely large dielectric permittivities (ε' > 104) have been extensively studied because of their potential for use in passive electronic devices. However, the unacceptable loss tangents (tanδ) and temperature instability with respect to ε' continue to be a significant hindrance to their development. In this study, a novel GD oxide, exhibiting an extremely large ε' value of approximately 7.55 × 104 and an extremely low tanδ value of approximately 0.007 at 103 Hz, has been reported. These remarkable properties were attributed to the synthesis of a Lu3+/Nb5+ co-doped TiO2 (LuNTO) ceramic containing an appropriate co-dopant concentration. Furthermore, the variation in the ε' values between the temperatures of −60 °C and 210 °C did not exceed ±15% of the reference value obtained at 25 °C. The effects of the grains, grain boundaries, and second phase particles on the dielectric properties were evaluated to determine the dielectric properties exhibited by LuNTO ceramics. A highly dense microstructure was obtained in the as-sintered ceramics. The existence of a LuNbTiO6 microwave-dielectric phase was confirmed when the co-dopant concentration was increased to 1%, thereby affecting the dielectric behavior of the LuNTO ceramics. The excellent dielectric properties exhibited by the LuNTO ceramics were attributed to their inhomogeneous microstructure. The microstructure was composed of semiconducting grains, consisting of Ti3+ ions formed by Nb5+ dopant ions, alongside ultra-high-resistance grain boundaries. The effects of the semiconducting grains, insulating grain boundaries (GBs), and secondary microwave phase particles on the dielectric relaxations are explained based on their interfacial polarizations. The results suggest that a significant enhancement of the GB properties is the key toward improvement of the GD properties, while the presence of second phase particles may not always be effective. [ABSTRACT FROM AUTHOR]

The Mg2+/Ta5+ codoped rutile TiO2 ceramic with a nominal composition (Mg1/3Ta2/3)0.01Ti0.99O2 was synthesized using a conventional solid-state reaction method and sintered at 1400 °C for 2 h. The pure phase of the rutile TiO2 structure with a highly dense microstructure was obtained. A high dielectric permittivity (2.9 × 104 at 103 Hz) with a low loss tangent (<0.025) was achieved in the as-sintered ceramic. After removing the outer surface, the dielectric permittivity of the polished ceramic increased from 2.9 × 104 to 6.0 × 104, while the loss tangent also increased (~0.11). The dielectric permittivity and loss tangent could be recovered to the initial value of the as-sintered ceramic by annealing the polished ceramic in air. Notably, in the temperature range of −60–200 °C, the dielectric permittivity (103 Hz) of the annealed ceramic was slightly dependent (<±4.4%), while the loss tangent was very low (0.015–0.036). The giant dielectric properties were likely contributed by the insulating grain boundaries and insulative surface layer effects. [ABSTRACT FROM AUTHOR]

• Twice-enhanced ε′ ≈ 1.65 × 104 → 3.81 × 104 was realized by doping with Mg. • Twofold reduced tanδ ≈ 0.227 → 0.081 was obtained. • ε′ was further enhanced to ~5.6 × 104 by codoping with Ge. • Further threefold reduction in tanδ to 0.026 was achieved. • Double-step reduced tanδ was attributed to the double-step enhanced R gb. Twice-enhanced dielectric permittivity for CaCu 3 Ti 4 O 12 with a twofold reduced loss tangent was realized by doping with Mg at the Cu site. The dielectric permittivity was further enhanced by codoping with Ge at the Ti site with a further threefold reduction in the loss tangent. Theoretical calculations showed that Mg and Ge are preferentially occupied at the Cu sites in the CaCu 3 Ti 4 O 12 structure. CaCu 2.95 Mg 0.05 Ti 4- x Ge x O 12 ceramics showed an enormous expansion of grain size with the segregation of Cu-rich phase along the grain boundary, which is likely attributed to the liquid phase sintering mechanism correlated to the preferential substitution of Ge ions. The enhancement of the dielectric permittivity originates from the enhanced ratio of mean grain size to grain boundary thickness and increased free charge inside the semiconducting grains, obeying a simple series-layer model of the internal barrier layer capacitor (IBLC). The dielectric properties can be well fitted by the Maxwell-Wagner polarization relaxation model based on the IBLC structure. Accordingly, a double-step reduction in the low-frequency loss tangent by only doping with Mg and further codoping with Ge ions was attributed to the double-step enhanced resistance of the insulating grain boundaries, which was due to the segregation of the Cu-rich phase. [ABSTRACT FROM AUTHOR]

In this work, the colossal dielectric properties and Maxwell—Wagner relaxation of TiO2–rich Na1/2Y1/2Cu3Ti4+xO12 (x = 0–0.2) ceramics prepared by a solid-state reaction method are investigated. A single phase of Na1/2Y1/2Cu3Ti4O12 is achieved without the detection of any impurity phase. The highly dense microstructure is obtained, and the mean grain size is significantly reduced by a factor of 10 by increasing Ti molar ratio, resulting in an increased grain boundary density and hence grain boundary resistance (Rgb). The colossal permittivities of ε′ ~ 0.7–1.4 × 104 with slightly dependent on frequency in the frequency range of 102–106 Hz are obtained in the TiO2–rich Na1/2Y1/2Cu3Ti4+xO12 ceramics, while the dielectric loss tangent is reduced to tanδ ~ 0.016–0.020 at 1 kHz due to the increased Rgb. The semiconducting grain resistance (Rg) of the Na1/2Y1/2Cu3Ti4+xO12 ceramics increases with increasing x, corresponding to the decrease in Cu+/Cu2+ ratio. The nonlinear electrical properties of the TiO2–rich Na1/2Y1/2Cu3Ti4+xO12 ceramics can also be improved. The colossal dielectric and nonlinear electrical properties of the TiO2–rich Na1/2Y1/2Cu3Ti4+xO12 ceramics are explained by the Maxwell–Wagner relaxation model based on the formation of the Schottky barrier at the grain boundary. [ABSTRACT FROM AUTHOR]

Giant dielectric ceramic, Na 1/2 Sm 1/2 Cu 3 Ti 4 O 12 , was successfully prepared by a modified sol-gel method. X-ray diffraction experiments indicated that a body-centered cubic structure with a space group of Im 3 was obtained. Our density functional theory calculations revealed that codoping Na and Sm in the CaCu 3 Ti 4 O 12 structure resulted in charge compensation between Na and Sm ions in this structure, whereas the oxidation states of Cu and Ti were unaltered. Giant dielectric permittivity ∼7.21 × 103 - 8.04 × 103 and low dielectric loss tangent ∼0.045–0.049 were accomplished at a sintering temperature of 1050 °C for 12–18 h. Nonlinear J - E property with breakdown electric field ∼5.13 – 5.78 × 103 V/cm and nonlinear coefficient ∼6.08–6.82 were also achieved. The n -type semiconducting grain originated from short-range migrations of mixed Cu+/Cu2+ and Ti3+/Ti4+ charges. Finally, our charge analysis showed that the occurrence of Cu+ and Ti3+ was related to the existence of oxygen vacancy in these ceramics. [ABSTRACT FROM AUTHOR]

Flexible dielectric polymer composites have been of great interest as embedded capacitor materials in the electronic industry. However, a polymer composite has a low relative dielectric permittivity (ε′ < 100), while its dielectric loss tangent is generally large (tanδ > 0.1). In this study, we fabricate a novel, high-permittivity polymer nanocomposite system with a low tanδ. The nanocomposite system comprises poly(vinylidene fluoride) (PVDF) co-filled with Au nanoparticles and semiconducting TiO2 nanorods (TNRs) that contain Ti3+ ions. To homogeneously disperse the conductive Au phase, the TNR surface was decorated with Au-NPs ~10–20 nm in size (Au-TNRs) using a modified Turkevich method. The polar β-PVDF phase was enhanced by the incorporation of the Au nanoparticles, partially contributing to the enhanced ε′ value. The introduction of the Au-TNRs in the PVDF matrix provided three-phase Au-TNR/PVDF nanocomposites with excellent dielectric properties (i.e., high ε′ ≈ 157 and low tanδ ≈ 0.05 at 1.8 vol% of Au and 47.4 vol% of TNRs). The ε′ of the three-phase Au-TNR/PVDF composite is ~2.4-times higher than that of the two-phase TNR/PVDF composite, clearly highlighting the primary contribution of the Au nanoparticles at similar filler loadings. The volume fraction dependence of ε′ is in close agreement with the effective medium percolation theory model. The significant enhancement in ε′ was primarily caused by interfacial polarization at the PVDF–conducting Au nanoparticle and PVDF–semiconducting TNR interfaces, as well as by the induced β-PVDF phase. A low tanδ was achieved due to the inhibited conducting pathway formed by direct Au nanoparticle contact. [ABSTRACT FROM AUTHOR]

• Glass systems of Li2S-2H3BO3: xCoN2O6.6H2O (x = 3, 4 and 5 mol%) were successfully prepared via melt-quenching method • Optical, magnetic and electrochemical properties of prepared glasses were investigated • The highest specific capacitance of 97.972 mV/s was obtained from glsss with x= 5 mol%. • XANES results reveal the S6+ and mixing Co2+/3+ oxidation states of all glasses • Difference of proportional site of Co atoms in both site of A-site and B-site is also presented by EXAFS Li 2 S-2H 3 BO 3 : xCoN 2 O 6.6H 2 O (x = 3, 4 and 5mol %) glass system was prepared. The microstructure and physical properties of glasses were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-Vis spectrophotometer and vibrating sample magnetometer (VSM). In order to measure the electrochemical properties of glasses, the cycling voltammograms (CVs) was employed where the highest specific capacitances of 97.972 mV/s was obtained from x= 5mol%. For structure-function of glasses, the S and Co oxidation states at S K -edge and Co K -edge and local structure around Co ions were studied by X-ray absorption spectroscopy (XAS) including X-ray absorption near edge structure (XANES) and extended X-ray absorption spectroscopy (EXAFS). It was found that, the S6+ oxidation state and mixing Co2+/3+ were revealed, respectively. Moreover, the Co K -edge EXAFS fitting was exhibited co-existence of Co A -O bond (tetrahedral coordination) and Co B -O bond (octahedral coordination) in all fabricated glasses with a difference proportional site. [ABSTRACT FROM AUTHOR]

(Co, Nb) co-doped rutile TiO2 (CoNTO) nanoparticles with low dopant concentrations were prepared using a wet chemistry method. A pure rutile TiO2 phase with a dense microstructure and homogeneous dispersion of the dopants was obtained. By co-doping rutile TiO2 with 0.5 at.% (Co, Nb), a very high dielectric permittivity of ε′ ≈ 36,105 and a low loss tangent of tanδ ≈ 0.04 were achieved. The sample–electrode contact and resistive outer-surface layer (surface barrier layer capacitor) have a significant impact on the dielectric response in the CoNTO ceramics. The density functional theory calculation shows that the 2Co atoms are located near the oxygen vacancy, creating a triangle-shaped 2CoVoTi complex defect. On the other hand, the substitution of TiO2 with Nb atoms can form a diamond-shaped 2Nb2Ti complex defect. These two types of complex defects are far away from each other. Therefore, the electron-pinned defect dipoles cannot be considered the primary origins of the dielectric response in the CoNTO ceramics. Impedance spectroscopy shows that the CoNTO ceramics are electrically heterogeneous, comprised of insulating and semiconducting regions. Thus, the dielectric properties of the CoNTO ceramics are attributed to the interfacial polarization at the internal insulating layers with very high resistivity, giving rise to a low loss tangent. [ABSTRACT FROM AUTHOR]

The effects of the sintering conditions on the phase compositions, microstructure, electrical properties, and dielectric responses of TiO2-excessive Na1/2Y1/2Cu3Ti4.1O12 ceramics prepared by a solid-state reaction method were investigated. A pure phase of the Na1/2Y1/2Cu3Ti4.1O12 ceramic was achieved in all sintered ceramics. The mean grain size slightly increased with increasing sintering time (from 1 to 15 h after sintering at 1070 °C) and sintering temperature from 1070 to 1090 °C for 5 h. The primary elements were dispersed in the microstructure. Low dielectric loss tangents (tan δ~0.018–0.022) were obtained. Moreover, the dielectric constant increased from ε′~5396 to 25,565 upon changing the sintering conditions. The lowest tan δ of 0.009 at 1 kHz was obtained. The electrical responses of the semiconducting grain and insulating grain boundary were studied using impedance and admittance spectroscopies. The breakdown voltage and nonlinear coefficient decreased significantly as the sintering temperature and time increased. The presence of Cu+, Cu3+, and Ti3+ was examined using X-ray photoelectron spectroscopy, confirming the formation of semiconducting grains. The dielectric and electrical properties were described using Maxwell–Wagner relaxation, based on the internal barrier layer capacitor model. [ABSTRACT FROM AUTHOR]

Lead‐free (Bi0.5Na0.5)0.7La0.3(Ti0.7Fe0.3)O3 ceramics (abbreviated as BNLTF) are synthesized by the solid‐state combustion technique using glycine as fuel. The effect of the firing temperature (calcined between 700 and 800 °C for 2 h and sintered between at 800 and 900 °C for 2 h) on the phase structure, microstructure, electrical, and magnetic properties is investigated. Pure BNLTF powders are obtained with a calcination temperature of 750 °C for 2 h and the crystal size increases from 47 to 62 nm when the calcination temperature increases from 700 to 800 °C. All sintered BNLTF ceramics show a pure perovskite structure with a rhombohedral phase. The average grain size increases with increasing sintering temperatures. A well‐packed microstructure with the highest density (5.98 g cm−3), good dielectric properties at room temperature (εr ≈ 589 and tanδ ≈ 0.572), soft ferroelectric behavior, and excellent magnetic properties (Ms ≈ 0.091 emu g−1, Mr ≈ 0.0026 emu g−1) is obtained from the ceramic sintered at 875 °C for 2 h. The multiferroic BNLTF ceramic sintered at 875 °C has a maximum magnetoelectric coupling coefficient (αE ≈ 2.08 mV cm−1 Oe−1) when the magnetic field is near 4500 Oe. [ABSTRACT FROM AUTHOR]

Herein, unloaded WO3 (WO3) and Pt‐loaded WO3 (Pt‐WO3) nanobars are successfully synthesized through simple hydrothermal and impregnation methods. X‐ray diffractometer analysis confirms the formation of a monoclinic WO3 structure. Surface analysis reveals that the Pt impregnation results in a significant increase in the specific surface area of WO3 nanobars. The gas‐sensing performance of sensors based on nanobars is measured toward ammonia (NH3) with varying NH3 concentrations at different operating temperatures. Compared with the pristine WO3 sensor, the Pt‐WO3‐based sensor with an optimal Pt content of 1 wt% exhibits a relatively low optimum operating temperature of 250 °C and a superior response of 960–50 ppm NH3. Furthermore, the Pt‐WO3‐based sensor also displays fast response, excellent NH3 selectivity to ammonia, moderate humidity dependence, and good stability. Therefore, the developed hydrothermal and impregnation methods could be a suitable alternative procedure for the synthesis of Pt‐WO3 nanobars useful for advanced NH3‐sensing applications. [ABSTRACT FROM AUTHOR]

Hydrogen adsorption performance and mechanism upon cycling of the upscaled Ni-doped hierarchical carbon scaffold (HCS) are investigated. Upon 22 hydrogen ad/desorption cycles (T = 25–50 °C and p (H 2) = 1–50 bar), the upscaled Ni-doped HCS shows excellent cycling stability with gravimetric capacity of up to 1.51 wt % H 2. This is due to mechanical stability of HCS and good distribution of Ni nanoparticles. Hydrogen adsorption mechanism of Ni-doped HCS upon cycling is experimentally and theoretically characterized. Besides dissociative adsorption onto the surface, hydrogen diffusion into the lattice structure of Ni is observed. The latter enhances with the number of ad/desorption cycles and alters the electron sharing mechanisms between Ni and H during adsorption. • First time upscaling Ni-doped hierarchical carbon scaffold (HCS) for storing H 2 at room temperature. • Excellent reversible capacity of 1.5 wt.% H 2 upon 22 ad/desorption cycles. • HCS with good mechanical stability and well-distributed Ni nanoparticles favoring cycling stability. • First time proposing hydrogen adsorption mechanism upon cycling of Ni-doped HCS. • Significant H diffusion into Ni lattice and deficient electron sharing of Ni with H upon cycling. [ABSTRACT FROM AUTHOR]

Diamond-like carbon (DLC) film properties are known to vary with important factors such as the ratio of sp3 to sp2 hybridization, film thickness, and contaminations. In this work, the carbon bonding contents in DLC thin films, thermal-treated with various temperatures between room temperature to 250 °C, were studies by near-edge X-ray absorption fine structure (NEXAFS), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. From NEXAFS measurements, the sp3/sp2 ratios of DLC films were found to be unaffected by the thermal treatments. The results indicate that thermal treatment below 250 °C does not affect the carbon bonding contents in DLC thin film. • DLC films with thermal treatment were studied using XPS, Raman and NEXAFS. • An agreement between XPS and Raman results were clearly illustrated. • Sp2 and sp3 hybridization peaks were used to understand the structure of DLC films. [ABSTRACT FROM AUTHOR]

Fly ash (FA) and sugarcane bagasse ash (SCBA) are the wastes from lignite power plants and sugar industries, usually disposed of as landfills. In this research, these wastes were effectively utilized as a construction material, namely geopolymer. The effect of the SCBA (0–40 wt.%) addition to the FA geopolymers was investigated. The compressive strength of the FA geopolymers was reduced with the SCBA addition. The reduction was mainly due to the presence of the highly stable and non-reactive quartz (SiO2) phase in SCBA. The SCBA was not dissolved in the alkaline activated solution and hence did not contribute to the geopolymerization process. The unreacted SCBA particles remained in the geopolymer matrix but did not provide strength. However, if the amount of SCBA was about 10 wt.% or less, the impact on the characteristics and properties of FA geopolymers was minimal. Furthermore, this research also studied the dielectric properties of the FA geopolymer/SCBA composites. The relatively large dielectric constant (ε′ = 3.6 × 103) was found for the pristine geopolymer. The addition of SCBA decreased the ε′ slightly due to high carbon content in SCBA. Nevertheless, the variation in ε′ was mainly controlled by the geopolymerization process to form the aluminosilicate gel structure. [ABSTRACT FROM AUTHOR]

• Aminopropyl-grafted Silica gel was simply prepared with ultrasound assistance. • Textural properties of the grafted silica gel were better than that from conventional preparation. • The grafted silica gel samples are active in aldol condensation of furfural and acetone. • Selectivity to furfurylbutenone as a major product was comparable to previous studies. This work focuses on the development of a simple method to prepare heterogeneous catalysts with tunable basicity and stability for aldol condensation of furfural and acetone. Silica gel was grafted by aminopropyltriethoxysilane (APTES) with 20, 30, 40 and 50 wt. % of APTES using probe-type ultrasonicator with a power of 130 W and a frequency of 20 kHz. The grafted samples were studied by XRD, SEM, N 2 sorption, FTIR, XPS, CHN and TG analysis, and CO 2 -TPD. The sonication facilitated the bond formation between APTES and the silica gel with less pore blocking than the conventional grafting method. The basicity of the samples was tunable with the quantity of APTES loading. The grafted samples were active catalysts for aldol condensation between furfural and acetone at 60 °C. The catalyst with 30 wt. % APTES grafting (30APS-U) provided a nearly complete furfural conversion and high furfurylbutenone selectivity. The conversion and selectivity increased with time and reached the highest values at 24 h. Thus, the catalysts with tunable basicity prepared by ultrasound-assisted grafting of silica with various APTES amounts were effective in furfural valorization. [ABSTRACT FROM AUTHOR]

Novel manganese-lithium borate glasses and its possibility as cathode materials in Li-ion battery are carefully investigated. The structure and phase formation of the prepared glasses, 0.3MnO 2 -0.7(Li x BO 2) with x = 0.25, 0.50, 0.75 and 1.00, were characterized using X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and X-ray photoelectron spectroscopy (XPS) techniques. All XRD patterns present broad and no detectable peaks which confirmed purely amorphous phase. The CV curves exhibit pseudo-capacitance behavior indicating the mixed oxidation state of Mn2+/Mn3+ corresponding to Mn K-edge results measured by X-ray absorption near edge structure (XANES). The average Mn–O bonding distance was found in the range of 2.08–2.14 Å. SEM and TEM depict the existence of elements and confirm the glassy state of the obtained glass samples. The optical, magnetic, and electrochemical properties of these glasses have been also investigated. Paramagnetic behaviors are found for glass samples with x = 0.25, 0.50 and 0.75, respectively. Unlike other glass samples, the weak ferromagnetic was found at x = 1.0 composition. Interestingly, the highest specific capacitance value of 52 F g−1 is also obtained for 0.3MnO 2 -0.7(Li 1.0 BO 2) glass suggesting a new promising glass electrode in future Li-ion battery. Image 1 • The 0.3MnO 2 -0.7(Li x BO 2) glasses were successfully prepared. • The coexistence of Mn2+ and Mn3+ is favorable for these novel glasses. • The weak ferromagnetic was found at x = 1.00 of lithium content. • As electrochemical test, these borate glasses can be used as cathode materials. [ABSTRACT FROM AUTHOR]

The applicability of CaCu 3 Ti 4 O 12 (CCTO) ceramics in modern microelectronics has been widely investigated; however, CaCu 3 Ti 4 O 12 suffers large loss tangents, which limits its applicability. We employed a solid-state reaction method to prepare a new cation–anion codoping system incorporating Sn and F ions that can reduce the loss tangent and improve the electrical properties of CaCu 3 Ti 4 O 12 ceramics. The microstructure, dielectric response, nonlinear current–voltage characteristics, and electrical properties of the grains and grain boundaries of the (Sn–F) codoped CCTO ceramics (SF-CCTO) were investigated. Sn strongly suppressed the grain growth by reducing the grain boundary mobility, while F enhanced the densification of the sintered ceramics. Both the dielectric permittivity and loss tangent of the SF-CCTO ceramics tended to decrease with decreasing mean grain size owing to the increased codopant concentration. Notably, a large dielectric permittivity of ~3 × 104 with a low loss tangent of ~0.5 was achieved. Moreover, the breakdown electric field of the SF-CCTO ceramic was increased from ~200 V/cm (for the undoped CCTO ceramic) to ~200 V/cm. The Schottky barrier height at the grain boundary was enhanced by doping CaCu 3 Ti 4 O 12 with Sn and F ions. The reduced loss tangent and enhanced nonlinear electrical properties were attributed to the significant increase in the total grain boundary resistance resulting from the reduced mean grain size and the increased potential barrier height. The nonlinear electrical properties and dielectric behavior is well described in terms of the internal barrier layer capacitor structure using the Maxwell–Wagner relaxation model. This method may be applied to other polycrystalline ceramics to improve their dielectric and nonlinear electrical properties. [ABSTRACT FROM AUTHOR]

In this study, cryptomelane-type manganese oxide (K-OMS-2) was used as a catalyst for the thermal oxidation of toluene. The catalyst was synthesized via the hydrothermal route and doped with Cu, Ce, and co-doped with the same metals by ex-situ and in-situ methods. The effects of dopant type, dopant concentration, and dopant impregnation method on the thermal catalytic activity of K-OMS-2 were examined. Initially, 1%, 2%, and 4% by mole Cu or Ce were incorporated by wet impregnation to the hydrothermally synthesized K-OMS-2 and in-situ direct hydrothermal method. The physicochemical properties were characterized by X-ray diffraction (XRD), N2 adsorption-desorption, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES), and thermal gravimetric analysis (TGA) techniques. Gaseous toluene was made to react with the doped catalysts in a packed bed reactor attached to gas chromatography equipment to measure the amount of unreacted toluene. Results showed K-OMS-2 doped with 4% by mole Cu and 1% by mole Ce gave excellent thermal catalytic efficiency results at 180 °C reaction temperature. Meanwhile, K-OMS-2 co-doped with Ce and Cu with a mole ratio of 0.25:3.75 per 100 moles of K-OMS-2 gave the best catalytic activity and complete oxidation at 180 °C reaction temperature. Comparing K-OMS-2 doped with the same metal ratios, in situ doped catalysts led to higher toluene removal percentages. Meanwhile, the 72-h stability test showed that the optimum co-doped catalysts are capable of entirely oxidizing toluene even after prolonged and continuous use. [ABSTRACT FROM AUTHOR]