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The rate capability of the AVNF//Al2O3@Zn was 108 mAh g-1 even at 20 A g-1, by employing the sonochemical method, which is the fast and efficient synthesis. The Zn anode were coated by Al2O3 of 9.9 nm, and therefore, the initial capacity is maintained to 94 % after 5,000 cycles even at 10 A g-1.

Exploring bifunctional electrocatalysts to lower the activation energy barriers for sluggish electrochemical reactions for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are of great importance in achieving lower energy consumption and higher conversion efficiency for future energy conversion and storage system. Despite the excellent performance of precious metal-based electrocatalysts for OER and ORR, their high cost and scarcity hamper their large-scale industrial application. As alternatives to precious metal-based electrocatalysts, the development of earth-abundant and efficient catalysts with excellent electrocatalytic performance in both the OER and the ORR is urgently required. Herein, we report a core-shell CoFeS

In this work, we prepared spinel-type NiCo2O4 (NCO) nanopowders as a low-cost and sensitive electrochemical sensor for nonenzymatic glucose detection. A facile and simple chemical bath method to synthesize the NCO nanopowders is demonstrated. The effect of pH and annealing temperature on the formation mechanism of NCO nanoparticles was systematically investigated. Our studies show that different pHs of the precursor solution during synthesis result in different intermediate phases and relating chemical reactions for the formation of NCO nanoparticles. Different morphologies of the NCO depending on pHs are also discussed based on the mechanism of growth. Electrochemical performance of the prepared NCO was characterized towards glucose, which reveals that sensitivity and selectivity of the NCO are significantly related with the final microstructure combined with constituent species with multiple oxidation states in the spinel structure.

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Recent technological progress towards the application of wearable electronic devices has prompted the development of flexible electrodes. To date, various technical approaches to improve the mechanical and electrical reliability of flexible electrodes have been reported; however, the transition from lab-scale processing to industrialization is still limited by complex processing steps involved in their preparation. Simple engineering steps are introduced to prepare flexible electrodes fabricated from silver-polydimethylsiloxane (Ag-PDMS) composites for wearable device applications. The electrical properties of the electrodes were investigated under stretching and bending conditions. Also, the effect of different Ag contents in the electrodes on electrical properties was investigated. As increasing the Ag content above 300 wt.%, Ag-PDMS electrodes exhibit electrical conductivity, which is closely related to the percolation threshold for the formation of a 3-D network of Ag in the PDMS matrix. Further increase of Ag content up to 450 wt.% resulted in electrical conductivity about 1000 S/cm, corresponding to an electrical resistivity of 1 mΩ cm. Furthermore, we investigated the electrical resistivity changes when repetitive stretching and bending deformation was applied. Based on the conceptual demonstration of a light-emitting diode circuit using Ag-PDMS electrodes, a simple printable electrode fabrication method can be applied to various stretchable electronic devices.

The influence of surface activated bonding (SAB) on adhesion strength between a metal and ceramic including Al/AlN and Cu/AlN is investigated. Plasma pre-treatments can significantly increase the adhesion strength between the metal and ceramic through surface activation, which can enlarge the contact area between metal and ceramic. Bonding pressure is also an important factor to improve the adhesion between metal and ceramic during SAB. Successful bonding between the metal and ceramic via SAB can be attributed to the formation of the interface layer where plastic deformation and rearrangement of metal to the ceramic occurs, which improves the atomic scale interconnection between the metal and ceramic. In this study, the influence of experimental SAB conditions for processing such as plasma power, degree of vacuum and bonding pressure on adhesion strength is investigated. Also, the thermal conduction of metal/ceramic laminates is discussed for its potential application as a heat spreader of LED chips.

Sr substituted BaTiO 3 (BST) nanopowders were prepared using oxalate co-precipitation methods. During synthesis, oxygen was applied to the oxalate solution in order to control the oxidation states of Ti. Control of pH in the solution results in different crystalline phases of the powders after calcination; pure perovskite BST was obtained in the powder prepared at pH 3 solution, while perovskite BaTiO 3 (BTO) and impurities were observed in powders prepared at pH 1 solution. Phase transformation from amorphous to crystalline BST during heat treatment was discussed by different analysis technique. Also, morphology and elemental distribution of the pure BST was investigated.

Effect of Fe incorporation on electrical properties of (NixCoyMn3-x-y)O4 (NMC) spinel compound is investigated for the application to a negative temperature coefficient (NTC) thermistor. Cation distribution of the Fe doped NMC (FNMC) is calculated based on the size of ions located at tetragonal A sites and octahedral B sites in spinel structure, which can be closely related with temperature dependent electrical properties of the FNMC. With change of Fe contents, the ratio of Mn3+/Mn4+ in octahedral B site of FNMC is changed which can determine the temperature sensitivity factor (B-value). Hopping conduction mode relating with activation energy and hopping distance was also discussed depending on Fe contents, based on the small polaron hopping theory.

(Ni,Co,Mn)O 4 (NMC) oxides were prepared by conventional sintering (CS) and spark plasma sintering (SPS) using micro and nanopowders. Small hoping polaron theory was used in order to investigate effect of processing routes on electrical properties of NMC oxides as negative temperature coefficient (NTC) thermistors. Also, X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) techniques were utilized to analyze compositional and structural effects on the electrical properties of NMC compounds. Hopping conduction in NMC prepared by SPS and CS using nanopowder occurs via variable range hopping (VRH) mechanism, however conduction in NMC prepared by CS using micropowder follows nearest neighboring hopping (NNH) mode. Hopping distance and activation energy for the VRH mode were calculated using corresponding physical model.

Transition–metal-doped carbon-based electrocatalysts have attracted attention as alternatives to noble metal electrocatalysts (e.g. IrO2 and RuO2) for oxygen evolution reaction (OER) because they are inexpensive and highly efficient. However, their poor catalytic activity and time-consuming synthesis remain a challenge. Herein, we report a facile and green technique using pulsed laser ablation for preparing Ni-doped multi-walled carbon nanotubes (Ni-MWCNTs) as OER catalysts. Ni-MWCNTs exhibit high surface area, oxygen-rich functional groups (e.g., hydroxyl and carboxyl), and successful doping of Ni in the carbon framework. The as-prepared Ni-MWCNTs exhibited excellent OER catalytic performance, with an overpotential of 320 mV at the current density of 10 mA cm−2 in an alkaline medium, which is lower than that of the commercial RuO2 catalyst. Furthermore, Ni-MWCNTs displayed the initial electrocatalytic activity after 10-h stability tests, demonstrating good electrochemical durability. We believe that this work provides a simple protocol for fabricating heteroatom-doped carbon nanotubes as high-performance OER electrocatalysts.

The formation of cation vacancies can be useful for electro-chemical devices. In this regard, an understanding of vacancy formation is an important subject for enhancing current electrochemical devices and for developing next generation energy devices. In this work, we chose the well-known lead-free ferroelectric (K0.5Na0.5)NbO3 (KNN) as a model system to understand both the formation of cation vacancies and the relationship between cation vacancies and the physical properties. We studied sintering-duration dependence of the dielectric properties and the cation contents of KNN ceramics at the temperatures near the melting point of KNN. The difference in sintering duration led to a drastic change in the dielectric property, as well as to the creation of cation vacancies. Interestingly, we observed unequal evaporation of cations during the sintering process, which was confirmed by the data obtained from laser-induced breakdown spectroscopy. In addition, we found more drastic changes in the imaginary dielectric constant, which were likely due to a decrease in ionic conducting species, such as K and Na, in KNN.

Fe-doped Ni-Mn-Co-O (FNMC) ceramics with the formula, (Fe x Ni 0.3 Co 0.9 Mn 1.8−x , x=0.1, 0.3, 0.5, and 0.7)O 4 were synthesized using a spray drying process. Effect of Fe content on the phase evolution of FNMC compound during heat treatment was studied using X-ray diffraction. A single phase cubic spinel structure with improved crystallinity was observed when the Fe content increased over 0.5. Fe, Ni, Mn and Co ions were homogeneously distributed in the sintered the FNMC ceramics, implying no phase separation occurred during sintering. The valence state of each element was analyzed using X-ray photoelectron spectroscopy, which revealed that Ni, Co, and Fe might have a single valence state while Mn had mixed valence states in the FNMC spinel compounds. The temperature-dependent electrical resistance for the FNMC ceramics was measured. Room temperature resistance and the B-value substantially increased for the FNMC samples with Fe content higher than 0.5. The electrical properties of FNMC compounds can be optimized by controlling the Fe content, which is directly indicative of their potential role as negative temperature coefficient sensors.

Co x Mn 3−x O 4 (CMO) nanopowders with a wide compositional range (0.9 ≤ x ≤ 2.7) are synthesized using a gel combustion method. The effect of Co content and calcination temperature on the crystal structure of the CMO nanopowders is studied using X-ray diffraction. A highly crystalline cubic spinel structure can be obtained at a relatively low temperature (~700 °C) for CMO with a Co content of 1.8. Further increases in Co content to 2.7 leads to a higher formation temperature (~800 °C) required in order to form a crystalline cubic structure. X-ray photoelectron spectroscopy revealed that the Co and Mn cations have mixed valence states. Energy dispersive X-ray elemental mapping indicates that Co and Mn cations are homogeneously distributed in the CMO nanopowders. Thermogravimetric analysis, Fourier transform infrared, scanning electron microscopy, and X-ray fluorescence are utilized to investigate the formation of the CMO nanopowders, as well as the compositional and structural properties.

Graphene oxide quantum dots (GOQDs) are usually prepared using expensive carbon precursors such as carbon nanotubes (CNT) or graphene under the strong acidic condition, which requires an additional purifying process. Here, we first develop a facile pulsed laser ablation in liquid (PLAL) technique for preparing GOQDs using earth-abundant and low-cost coal as a precursor. Only ethanol and coal are used to produce GOQDs with excellent optical properties. The prepared GOQDs exhibit excellent optoelectronic properties which can be successfully utilized in bioimaging applications.

The reliability of negative temperature coefficient (NTC) thermistors is one of the important factors for the excellent performance of the battery management system in electric vehicles. The electrical properties of the thermistor can be explained by the indirect electron jump between Mn3+ and Mn4+ at the B-sites in a spinel-type thermistor. Additionally, different types of dopants, such as Fe, Cu, Zn, Cr, and Mn, are considered as electrical modifiers that can further improve the electrical properties of the thermistor. For example, Cu is often added to NTC thermistors, occupying the octahedral sites in a spinel-type thermistor, which can play an important role in conduction with the Mn cations. Addition of Fe is also widely used in NTC thermistors owing to its high sensitivity, B constant, and stability. In this study, composition-dependent structural and electrical properties of Cu0.2/Fey-co-doped Ni0.3Mna-x-yCo0.9O4 (NMC) are investigated. Cu/Fe-co-doped NMC shows the R25 and B25/85 constant values of 4490–12730 Ω and 3185–3490 K, respectively, exhibiting a typical ρ–T curve of NTC thermistors. Higher B constant and reliable electrical stability are observed for Cu/Fe-co-doped NMC. Based on the relationship between the cationic oxidation states and electrical properties of Cu/Fe-co-doped NMC, the hopping conduction mechanism is discussed.

Crystal structures and hopping motions of cobalt manganese spinel oxides across a wide composition range (CoxMn3−xO4 (CMO), 0.9 ≤ x ≤ 2.7) are investigated in order to clarify the corresponding mechanisms of electrical behaviors as negative temperature coefficient thermistors. Based on the diffraction measurements, a tetragonal to cubic spinel transition are observed mostly with increasing Co content. Hopping distance for a series of CMO are calculated by the variable range hopping mechanism, which is changed as a function of composition, resulting to the observed unique electrical properties. According to the electrical and structural analysis, the electrical properties of CMO compounds with different Co contents majorly determined by tetragonal to cubic phase transition, cation distribution, and hopping distance. In addition, the formation of secondary phase (i.e., CoO) and another CMO phase may also significantly affect the electrical properties.

Phase evolution of (Ni, Co, Mn)O 4 (NMC) for negative thermal coefficient (NTC) thermistor is investigated using high temperature X-ray diffraction. Diffraction patterns were collected during heating and cooling, allowing the observation of chemical reactions in the range of temperature between 25 and 1400 °C. NiO, Mn 3 O 4 and CO 3 O 4 as the reactant materials were prepared using spray drying. As increasing temperature, phase transformation of Mn 3 O 4 to Mn 2 O 3 was first observed prior to the formation of NMC spinel structure at 700 °C. Between 1000 and 1200 °C, only spinel NMC was observed without any other phases. Also, grain growth of NMC was observed. Phase transition from cubic to tetragonal was observed during cooling. With further increasing temperature up to 1400 °C, thermal stability of NMC decrease, which was confirmed by NiO separation due to the thermal decomposition. Thermogravimetric and differential thermal analysis are performed on NMC compound and the results support the mechanism of phase formation presented by high temperature XRD data. Also, electrical resistance of NMC is measured as a function of temperature (−40–80 °C) and the factor of thermal sensitivity ( B value) is calculated.

The pulsed laser fragmentation in liquid (PLFL) process is a promising technique for the synthesis of carbon‐based functional materials. However, a fundamental deep understanding of the formation of graphene quantum dots (GQDs) from multiwalled carbon nanotubes (MWCNTs) by PLFL has still not been achieved despite the high demand. In article number 2003538, Jeong Ho Ryu, Hyuksu Han, Kang Min Kim, and co‐workers report a mechanism for the formation of GQDs from MWCNTs by the PLFL process, through the combination of experimental and theoretical studies.

A novel Ce3+-doped Lu3MgAl3SiO12 (LCMAS) phosphor was successfully synthesized by a conventional solid-state reaction. The crystal structure of the LCMAS was characterized by Rietveld refinement. The broad emission spectra of the LCMAS were observed at 550 nm, and the temperature dependence on photoluminescence properties of the LCMAS was investigated. Also, the activation energy for thermal quenching was determined by Arrhenius fitting. The experimental results clearly indicate that the LCMAS phosphor has a great potential for the down-conversion of yellow phosphor into white light-emitting diodes.

Lead-free piezoelectric materials have been actively studied to substitute for conventional PZT based solid solution, , which occurs unavoidable PbO during the sintering process. Among them, Bismuth Sodium Titanate, (abbreviated as NBT) based solid solution is attracted for the one of excellent candidates which shows the strong ferroelectricity, Curie temperature (Tc), remnant polarization (Pr) and coercive field (Ec). Especially, the solid solution of rhombohedral phase NBT with tetragonal perovskite phase has a rhombohedral - tetragonal morphotropic phase boundary. Modified NBT with tetragonal perovskite at the region of MPB can be applied for high frequency ultrasonic application because of not only its low permittivity, high electrocoupling factor and high mechanical strength, but also effective piezoelectric activity by poling. In this study, solid state ceramic processing of NBT and modified NBT, (abbreviated as NBT-7BT), at the region of MPB using 7 % as a tetragonal perovskite was introduced and the structure between NBT and NBT-7BT were analyzed using rietveld refinement. Also, the ferroelectric and piezoelectric properties of NBT-7BT such as permittivity, piezoelectric constant, polarization hysteresis and strain hysteresis loop were compared with those of pure NBT.

The crystallization of lead zirconate titanate (PZT) thin films was evaluated on two different platinum-coated Si substrates. One substrate consisted of a Pt coating on a Ti adhesion layer, whereas the other consisted of a Pt coating on a TiO2 adhesion layer. The Pt deposited on TiO2 exhibited a higher degree of preferred orientation than the Pt deposited on Ti (as measured by the Full Width at Half Maximum of the 111 peak about the sample normal). PZT thin films with a nominal Zr/Ti ratio of 52/48 were deposited on the substrates using the inverted mixing order (IMO) route. Phase and texture evolution of the thin films were monitored during crystallization using in situ X-ray diffraction at a synchrotron source. The intensity of the Pt3Pb phase indicated that deposition on a highly oriented Pt/TiO2 substrate resulted in less diffusion of Pb into the substrate relative to films deposited on Pt/Ti. There was also no evidence of the pyrochlore phase influencing texture evolution. The results suggest that PZT nucleates directly on Pt, which explains the observation of a more highly oriented 111 texture of PZT on the Pt/TiO2 substrate than on the Pt/Ti substrate.

Graphene quantum dots (GQDs) have attractive properties and potential applications. However, their various applications are limited by a current synthetic method which requires long processing time. Here, we report a facile and remarkably rapid method for production of GQDs exhibiting excellent optoelectronic properties. We employed the pulsed laser ablation (PLA) technique to exfoliate GQDs from multi-wall carbon nanotube (MWCNTs), which can be referred to as a pulsed laser exfoliation (PLE) process. Strikingly, it takes only 6 min to transform all MWCNTs precursors to GQDs by using PLE process. Furthermore, we could selectively produce either GQDs or graphene oxide quantum dots (GOQDs) by simply changing the organic solvents utilized in the PLE processing. The synthesized GQDs show distinct blue photoluminescence (PL) with excellent quantum yield (QY) up to 12% as well as sufficient brightness and resolution to be suitable for optoelectronic applications. We believe that the PLE process proposed in this work will further open up new routes for the preparation of different optoelectronic nanomaterials.

High-performance oxygen evolution reaction (OER) electrocatalysts are needed to produce hydrogen for energy generation through a carbon-free route. In this work, the solution combustion synthesis (SCS) method was employed to synthesize mixed phases of Co- and Mn-based oxides, and the relationships between the crystalline structure and the catalytic properties in the mixed phases were established. The mixed phases of Co- and Mn-based oxides shows promising OER properties, such as acceptable overpotential (450 mV for 10 mA∙cm&minus, 2) and Tafel slope (35.8 mV∙dec&minus, 1), highlighting the use of the mixed phases of Co- and Mn-based oxides as a new efficient catalysts for water splitting. Electronic structure of the mixed phases of Co- and Mn based oxides is studied in detail to give insight for the origin of high catalytic activities. In addition, excellent long-term stability for OER in alkaline media is achieved for the mixed phase of Co- and Mn based oxides.

The crystallization behavior of solution-derived lead zirconate titanate (PZT) thin films in different atmospheric environments was studied using in situ X-ray diffraction. The stability of the transient intermetallic Pt3Pb phase and perovskite PZT is dependent on oxygen partial pressure during crystallization. Based on the relationship between oxygen partial pressure and the resultant phase stability of intermediate phases, a new route to produce PZT thin films was developed. The new route involves switching atmospheres during crystallization and is shown to mitigate the formation of the transient intermetallic Pt3Pb phase and to promote the perovskite PZT phase. The route evidences a new and significant variable controlling film synthesis and film microstructure.

International audience; Hopping motions in cobalt manganese spinel oxides with high cobalt concentration (CoxMn3−xO4, 2.3 ≤ x ≤ 2.7) are investigated in order to clarify the origin of unusual electrical behaviors as negative temperature coefficient (NTC) thermistors. Based on the resistance versus temperature (R−T) characteristics, hopping conduction mechanisms in MCO compounds (x = 2.3 and 2.5) are attributed to variable range hopping (VRH) motion with a parabolic distribution of the density of states (DOS) near the Fermi level. However, when Co content increases up to 2.7, transition in the hopping motion occurs from VRH to the nearest neighboring hopping (NNH) motion, which can be responsible for a huge increase of the resistance accompanied by decrease of the factor of thermal sensitivity (B value) in MCO compounds (x = 2.7). Also, hopping distance and activation energies for MCO (x = 2.3 and 2.5) compounds following VRH conduction are calculated as a function of temperature, indicating that higher B value observed in MCO (x = 2.5) compound is due to the larger hopping distance compared to that of MCO (x = 2.3) compound.

Epitaxial Ba2FeMoO6 thin films were grown via pulsed laser deposition under low oxygen pressure and their structural, chemical, and magnetic properties were examined, focusing on the effects of oxygen pressure. The chemical disorder, off-stoichiometry in B site cations (Fe and Mo) increased with increasing oxygen pressure and thus magnetic properties were degraded. Interestingly, in contrast, negative magneto-resistance, which is the characteristics of this double perovskite material, was enhanced with increasing oxygen pressure. It is believed that phase segregation of highly disordered thin films is responsible for the increased magneto-resistance of thin films grown at high oxygen pressure. The anomalous Hall effect, which behaves hole-like, was also observed due to spin-polarized itinerant electrons under low magnetic field below 1 T and the ordinary electron-like Hall effect was dominant at higher magnetic fields.

The authors report a novel synthetic route for Ho3+/Yb3+ codoped calcium molybdate (CaMoO4) nanoparticles by pulsed laser ablation in ethanol. Well-dispersed Ho3+/Yb3+ codoped CaMoO4 nanocolloid was prepared without any surfactant. Crystallographic information, microstructure, and the upconversion (UC) luminescent properties of the nanocolloid were investigated. Under the excitation at 980 nm, Ho3+/Yb3+ codoped CaMoO4 nanocolloid exhibited strong yellow emission visible to the naked eyes, which is the combination of green emission near 542 nm and strong red emission around 656 nm. Based on the pump power dependence, UC mechanism of Ho3+/Yb3+ codoped CaMoO4 nanocolloid was discussed in detail.

Cerium-doped Tb3Al5O12(TAG:Ce3+) colloidal nanocrystals were synthesized by pulsed laser ablation (PLA) in de-ionized water and lauryl dimethylaminoacetic acid betain (LDA) aqueous solution for luminescent bio-labeling application. The influence of LDA molecules on the crystallinity, crystal morphology, crystallite size, and luminescent properties of the prepared TAG:Ce3+colloidal nanocrystals was investigated in detail. When the LDA solution was used, smaller average crystallite size, narrower size distribution, and enhanced luminescence were observed. These characteristics were explained by the effective role of occupying the oxygen defects on the surface of TAG:Ce3+colloidal nanocrystal because the amphoteric LDA molecules were attached by positively charged TAG:Ce3+colloidal nanocrystals. The blue-shifted phenomena found in luminescent spectra of the TAG:Ce3+colloidal nanocrystals could not be explained by previous crystal field theory. We discuss the 5d energy level of Ce3+with decreased crystal size with a phenomenological model that explains the relationship between bond distance with 5d energy level of Ce3+based on the concept of crystal field theory modified by covalency contribution.