Search

Molybdenum disulfide (MoS 2) is one of the most explored prospective materials for building effective supercapacitors (SCs). However, low energy density hinders their efficiency due to poor electrical conductivity and deficient active sites. We designed a binder-free MoS 2 /CoS composite with nickel foam (NF) as a substrate to address these concerns. XRD, SEM, EDS and XPS were used to examine the structural and morphological development of the MoS 2 /CoS composite. The capacitive performance of MoS 2 /CoS electrodes was determined using CV, GCD and EIS. For the three-electrode system, the area specific capacitance of the MoS 2 /CoS electrodes was 180 mF/cm2 and 1931 mF/cm2 in Na 2 SO 4 and KOH electrolytes respectively, with a current density of 5 mA/cm2. Also, the energy densities of SCs assembled in Na 2 SO 4 , and KOH electrolytes were 36.62 μWh/cm2 and 268.33 μWh/cm2, with power densities of 1345.22 μW/cm2 and 2100 μW/cm2, respectively. After 3000 cycles, the cycling stability of the devices in Na 2 SO 4 (and KOH) electrolyte was about 71.2% (and 73.3%), implying good electrochemical stability of the devices. These results indicate the potential application of binder-free MoS 2 /CoS composites as electrode materials for aqueous SCs in KOH and Na 2 SO 4 electrolytes. • MoS 2 /CoS composite was prepared by a simple SILAR method. • The area specific capacitance of MoS 2 /CoS composites in KOH electrolyte was 1931 mF/cm2 at 1 mA/cm2. • The SSC exhibits an energy density of 268.33 μWh/cm2 with a power density of 2100 μW/cm2 in a KOH electrolyte. [ABSTRACT FROM AUTHOR]

This work reports a simple, eco-benign, pollution-free two-step electrodeposition technology to prepare NiCo 2 S 4 /MoS x composites on nickel foam (NF). It was then employed as electrodes for all-solid symmetric supercapacitors. The NiCo 2 S 4 / MoS x /NF composite can provide a superior specific capacity of 1494.52 F/g at 1 A/g, and also deliver good stability of ∼93.03% after 1000 cycles. The NiCo 2 S 4 /MoS x /NF was assembled as the positive and negative electrodes of an all-solid symmetric supercapacitor (NiCo 2 S 4 /MoS x /NF // NiCo 2 S 4 /MoS x /NF). This assembly exhibits an energy density of 32.54 Wh/kg with the power density 285.72 W/kg, and superior cycle life retention rate of 84.46% and Coulombic efficiency of 100% after 1000 charge-discharge cycles, respectively. The excellent electrochemical property of the NiCo 2 S 4 /MoS x /NF composite is ascribed to the synergistic effect between the MoS x and NiCo 2 S 4 , suggesting it has excellent prospects as an electrode for supercapacitors. • The NiCo 2 S 4 /MoS x /NF electrode was successfully prepared by two-step electrochemical deposition. • The NiCo 2 S 4 /MoS x /NF electrode exhibits a specific capacitance of 1494.52 F/g at 1 A/g in a three-electrode system. • The NiCo 2 S 4 /MoS x /NF // NiCo 2 S 4 /MoS x /NF device exhibits a high energy density of 32.54 Wh/kg and excellent power density of 285.72 W/kg. [ABSTRACT FROM AUTHOR]

The high pressure (HP) structural phase of FeB 2 compound is investigated by using first-principles crystal structure prediction based on the CALYPSO technique. A thermodynamically stable phase of FeB 2 with space group Imma is predicted at pressure above 225 GPa, which is characterized by a layered orthorhombic structure containing puckered graphite-like boron layers. Its electronic and mechanical properties are identified and analyzed. The feature of band structures favors the occurrence of superconductivity, whereas, the calculated Pugh's ratio reveals that the HP Imma structure exhibits ductile mechanical property. [ABSTRACT FROM AUTHOR]

Abstract: Holmium doped sodium gadolinium tungstate crystals with sizes of about Ø20mm×40mm were grown successfully by the Czochralski technique along the (001) orientation. Polarized absorption spectra, fluorescence spectra and fluorescence decay curve of Ho3+-doped NaGd(WO4)2 have been recorded at room temperature. Based on the Judd–Ofelt theory, three intensity parameters were obtained. The spectroscopic parameters of this crystal such as the oscillator strengths, radiative transition probabilities, radiative lifetimes as well as the branching ratios were calculated. The fluorescence lifetime τ f of the 5S2 level was measured to be 5μs. [Copyright &y& Elsevier]

Phase transitions are widely observed in many metal materials including amorphous alloy and high-entropy alloys (HEAs). When HEAs are made in the amorphous form, is it possible for the amorphous phase to transition to simple solid solution? This paper reveals a phase transition from amorphous phase to body-centered cubic (bcc) phase and then to face-centered cubic (fcc) phase in Fe 30 Co 29 Ni 29 Zr 7 B 4 Cu 1 HEA by employing simple heat treatment process. Accordingly, the intrinsic correlation between the microstructure and soft-magnetic properties was established by excluding the composition interference. The explanation of mechanism behind the phase transitions was explored by first-principles density functional theory (DFT) calculations and other methods. This research suggests an approach of designing HEAs with excellent magnetic properties, and provides a prototype to study structure of amorphous alloys. • HEAs with amorphous, bcc or fcc structure were prepared, respectively. • The phase transitions mechanism was investigated by DFT calculations. • The B s of the HEAs is bcc > amorphous ≈ fcc. • The variation of B s was revealed DFT calculations. [ABSTRACT FROM AUTHOR]

Being as the most abundant natural mineral among the iron-based sulphides, iron pyrite (FeS 2 ) has been extensively investigated. These investigations mainly focused on the known marcasite ( Pnnm ) and pyrite ( P a 3 ¯ ) phases, due to unknown of high pressure (HP) structural phases of FeS 2 . Here, we report a theoretical study up to 300 GPa to uncover a brand new monoclinic HP phase of C 2/ m structure at above 192 GPa. The stable of this structure is evaluated by the thermodynamical, dynamical and mechanical calculations. The C 2/ m structure is characterized by distorted FeS 6 octahedron together with two connected 1D zigzag-like S chains. Analysis of the thermoelectric calculations indicates that the electronic thermal conductivity and electrical conductivity of C 2/ m structure linearly increasing with increasing temperature. Meanwhile, it is found that the C 2/ m phase behaves in a ductile manner through the elastic parameters calculations. [ABSTRACT FROM AUTHOR]

A systematically investigation of Ti-Ga intermetallic compounds was performed to explore their mechanical and thermodynamic properties using density functional theory (DFT). Based on the experimental and theoretical reported data, a series of Ti-Ga alloys are chosen to study in this work. By assessing the elastic property of Ti-Ga alloys including bulk modulus, shear modulus, Young's modulus and Poisson's ratio, the results indicate that these Ti-Ga alloys are mechanically stable. The Pugh's ratio B/G is calculated to reveal that these Ti-Ga alloys display ductile character, except for Ga 3 Ti and Ga 3 Ti 2 . Meanwhile, the anisotropy factor A and Vickers hardness H V are studied, and the hardness is found in the order: Ga 3 Ti>Ga 3 Ti 2 >Ga 3 Ti 5 >GaTi 2 >GaTi>GaTi 3 . Furthermore, the thermodynamic property is predicted by means of different empirical formulae, the results reveal that the alloys exhibit more high melting point and thermal conductivity. By the evaluation of the heat capacity with temperature 0–80 K, indicating that the electron excitations plays a main role below 17 K, while the phonon excitations mainly contribute to the heat capacity in the range of 31–80 K. [ABSTRACT FROM AUTHOR]

Nanostructured materials present another alternative solution to improving the performance of gas sensors, which depends largely on their morphology. In this paper, the effects of different TiO 2 nanostructures on the gas sensing properties of NH 3 are explored through both experimentation and molecular dyanamics (MD) simulation. During the experiment, TiO 2 nanofilms, upright nanorods and zigzag nanorods are produced by means of glancing angle deposition (GLAD), while the nanostructures are characterized by scanning electron microscopy and X-ray powder diffraction. The test on concentration gradient, repeatability, and selectivity of NH 3 is conducted at room temperature. It is demonstrated that the nanostructures with distinct morphologies vary in gas sensing properties for NH 3. Notably, the 1 fold zigzag nanostructure outperforms other structures in NH 3 response. During the simulation process, the performance of various structures in adsorbing gas molecules is simulated through molecular dynamics to verify the relevant experimental results. Both experimental and simulation results show that 1 fold zigzag nanostructures are promising in terms of NH 3 sensing. • Zigzag TiO 2 nanorods for NH 3 detection were prepared by GLAD. • Corresponding molecular dynamics models for the sensor were established. • The one-fold nanorods showed the best response to NH 3. • The sensing mechanism was performed in detail. [ABSTRACT FROM AUTHOR]

Abstract: The single crystal of ZnWO4:Ho3+ was grown by Czochralski technique. The XRD, absorption spectra, fluorescence spectrum are presented, and the Judd–Ofelt (J–O) intensity parameters Ω 2, Ω 4, Ω 6 are obtained to be 4.61×10−20 cm2, 0.16×10−20 cm2, 0.48×10−20 cm2, respectively. Calculated radiative transition rate, branching ratios, and radiative lifetime for different transition levels of ZnWO4:Ho3+crystals are presented. The most intense line correlative with the transition 5S2 → 5I8 at 543nm is potentially used for green solid state laser, and the fluorescence lifetime of this energy level is 14.1μs. [Copyright &y& Elsevier]

Abstract: NaLa(WO4)2:Dy3+ crystals were grown successfully by the Czochraski technique. The Raman, infrared, electronic absorption and emission spectra were measured at room temperature. The Judd–Ofelt theory, extended to anisotropic system, has been applied to evaluate the intensity parameters Ω t (t =2, 4, 6), radiative transition rates A, radiative lifetimes τ R, and fluorescent branching ratios β. Although there are several transitions originating in the 4F9/2 level, a major part of emission intensity is contained in the 4F9/2 → 6H13/2 transition. The stimulated emission cross-sections for this transition were estimated by using the Füchtbauer–Ladenburg method. The luminescence decay curve was also measured at room temperature. The results indicate that NaLa(WO4)2:Dy3+ may be considered as laser active materials operating near 0.57μm. [Copyright &y& Elsevier]

Recent research interest has increased in the production of heteroatoms-doped porous carbon with controlled morphology from biomass. However, there is still a significant challenge in resolving alkaline solutions that cause equipment corrosion and devising a simple and adaptable approach. In this study, N/O/S co-doped honeycomb-like porous carbons were synthesized from a widely cultivated annual weed (Hemistepta Iyrata Bunge) using a simple and eco-friendly method. The sodium hydroxide (NaOH)/urea system was utilized as the pore-forming agent and cellulose solvent, with urea as the nitrogen source. By varying the activation temperature, the as-prepared porous carbon has a high specific surface area (709 m2 g−1), a large total pore volume (0.44 cm3 g−1), and a high heteroatom content of 6.20 at% nitrogen and 8.12 at% oxygen. The prepared porous materials were evaluated as electrodes for supercapacitors. The product (HIB-PHC-750 °C) exhibited a high specific capacitance (353.6 F g−1 at 0.2 A g−1) at a carbonization temperature of 750 °C. Additionally, the HIB-PHC-750 °C-based symmetric device with a wide voltage range of 2.0 V possessed a desirable energy density of 44.22 Wh kg−1 at 500 W kg−1. Moreover, the HIB-PHC-750 °C also demonstrated outstanding cycling stability with 98.2 % capacitance retention after 10,000 cycles. This research provided a facile and favorable alternative method for preparing N/O/S co-doped honeycomb-like porous carbon for electrochemical energy storage devices. [Display omitted] • Honeycomb-like hierarchical porous carbons were prepared with Hemistepta Iyrata Bunge as the carbon source. • NaOH was utilized as the activating agent and urea was used as nitrogen source. • The sample possesses a high surface area and high N/O content. • The carbons exhibit high specific capacitance, voltage and cyclic stability. [ABSTRACT FROM AUTHOR]

Abstract Recently spotlighting on lithium disulfide (Li 2 S 2) as an intermediate product of a promising high capacity lithium–sulfur (Li S) battery, a structure of P 4 2 / mnm had been proposed for understanding the existence of Li 2 S 2 in Li S battery. Here using first-principles unbiased CALYPSO structure searching calculations, we uncovered a new energetically favored structural phase (P 2 1 / c) of Li 2 S 2 , being more stable than the P 4 2 / mnm structure at above 2.78 GPa. This predicted P 2 1 / c structure possess a similar quasi-molecular S 2 and Li atoms in the interstice of S 2 with P 4 2 / mnm structure, but having a denser polyhedral packing (LiS 6) with Li atoms six-fold coordination in contract to the four-fold coordinated LiS 4 polyhedron of P 4 2 / mnm. Further, a calculated discharge voltage of 2.34 V was obtained for 2Li+ + 2e− + Li 2 S 2 →2Li 2 S and comparable to that of P 4 2 / mnm. Adopting CI-NEB method, we calculated the diffusion barrier and diffusion coefficient of Li ions with a high diffusion coefficient of 5.98 × 10−2 / cm2 s−1. This character reflects that it can acts as an intermediate product like as P 4 2 / mnm in a Li S battery. This work has a value in exposing the pressure–induced phase of Li 2 S 2 and enriching the views for understanding in Li S batteries. Highlights • A new pressure–induced phase (P 2 1 / c) of Li 2 S 2 is proposed and compared with P 4 2 / mnm. • The P 2 1 / c structure possesses quasi-molecular S 2 and forms Li six-fold coordination. • The discharge voltage was obtained for 2Li+ + 2e− + Li 2 S 2.→2Li 2 S in P 2 1 / c structure. • A high diffusion coefficient of Li ions was revealed in the P 2 1 / c structure. • The P 2 1 / c structure exhibits close to intermediate product character of Li S battery. [ABSTRACT FROM AUTHOR]

Memristors with a two-terminal structure are considered to be one of the most promising electronic devices capable of overcoming the Von Neumann bottleneck, which is highly anticipated in the post-Moore era and next-generation artificial intelligence applications. In this work, a memristive device was fabricated using a WO x /BiFeO y heterojunction as functional layer on F-doped SnO 2 (FTO) substrate by magnetron sputtering. The Ag/WO x /BiFeO y /FTO device exhibits enhanced bipolar nonvolatile resistive switching (RS) memory behavior compared with single-layer BiFeO y -based memristors, which can meet the requirements of high-density information storage. By performing a comprehensive conductivity analysis on the current-voltage (I-V) curve, it was proposed a reasonable physical model to explain the RS memory behavior of the device based on space-charge-limited current (SCLC) mechanism and the Schottky emission. Therefore, this work indicates that the bilayer WO x /BiFeO y heterojunction as functional layer can effectively improve the performance of memristive devices, which will further expand the application of ferroelectric/metal oxide heterojunction in the field of memristors. [Display omitted] • A memristive device was fabricated using a WO x /BiFeO y heterojunction as functional layer. • The Ag/WO x /BiFeO y /FTO device exhibits enhanced bipolar resistive switching behavior. • The bilayer WO x /BiFeO y heterojunction is an advanced functional layer of memristive device. • SCLC assisted Schottky barriers model is proposed to explain the resistive switching effect. • This work expands the application of ferroelectric/metal oxide heterojunctions in memristors. [ABSTRACT FROM AUTHOR]

Using the unbiased structure searching CALYPSO techniques and the first-principles calculations, we predicted a phase transition in iron pernitride (FeN 2 ) at 22 GPa from the hexagonal R -3 m structure to an orthorhombic Pnnm structure. Although the Pnnm structure is a well-known marcasite phase of transition-metal pernitrides, to our knowledge, this is the first report about the pressure-induced phase transition to the Pnnm structure in the FeN 2 compound. The dynamically and mechanically stable for the Pnnm phase are evaluated, further confirming this phase transition. By assessing the elastic property of the Pnnm structure, the result indicates that it displays excellent brittle and hardness characters. Viewing it's structure, a dinitrogen unit and a coordinating iron atom characterized by N-sharing six-fold FeN 6 octahedrons are found. Based on the quantum-chemical analysis, the dinitrogen unit was formulated as a quasi-molecular double-bonded N 2 2− and a mixed covalent N N and Fe N bonding nature was identified in the structure. These structural and covalent bonding characters play a crucial role to its excellent mechanical properties. The present results extend the well-known marcasite phase in other transition-metal pernitrides to the FeN 2 compound and provide a perspective toward the understanding of the synthesis and chemical bonding of N-rich FeN 2 under high pressure. [ABSTRACT FROM AUTHOR]

Lanthanide-based optical ratiometric thermometer is a promising temperature detecting tool for noninvasive temperature measurements. However, owing to the thermal quenching of upconversion luminescence (UCL), the traditional temperature sensing range is limited to less than 600 K. In this work, highly thermally stable UCL is observed through introduced appropriate Cu2+ ions into LiYF 4 :Yb/Er (20/2 mol%) microcrystals (MCs) and on which are further used for temperature sensing applications. As gradually increases the doping of Cu2+ ions, the octahedron morphology of LiYF 4 MCs with smooth surfaces gradually aggregates smaller particles on their surface forming diamond-like micro-clusters. Based on the single-particle spectroscopy technique, the temperature-dependent UCL properties were systematically investigated and demonstrated. Doping of Cu2+ ions can efficiently adjust and enhance the UCL in the LiYF 4 :Yb/Er (20/2 mol%) MCs. The UCL thermal quenching temperature is less than ~670 K for Cu2+-free MCs. In contrast, the quenching temperature extends to as high as ~870 K when doping with 2 mol% Cu2+ ions. Furthermore, these highly thermal stable MCs are utilized to detect the temperature in a wide temperature ranging from 298 K to 873 K. A maximum relative sensitivity (S r) of 1.23%K−1 at 298 K is obtained and temperature uncertainty δ T < 0.091 K is determined under the measured temperature for the 2 mol% Cu2+-doped MCs. The highly thermally stable UCL properties and excellent thermometer performance of these MCs, particularly conducted at single-particle spectroscopy technique, can be potentially applied to micro-scale thermometers. • Cu2+ ions manipulate the morphology and size of LiYF 4 :Yb3+/Er3+ microcrystals. • Appropriate Cu2+ ions improve the upconversion luminescence thermostability. • High-temperature thermometers achieved at single-particle spectroscopy technique. [ABSTRACT FROM AUTHOR]

Highlights: [•] Yb3+-doped NYW with different concentrations have been grown by Czochralski method. [•] The optimum concentration of Yb3+-doped in NYW was predicted by comparing their optical properties. [•] The dual-polarization and dual-wavelength laser properties of NYW with 10at% Yb3+ doped have been tested. [•] The stable dual-polarization and dual-wavelength laser output have been realized with different output mirrors. [Copyright &y& Elsevier]

Abstract: A combined BaZrO3 (BZO) and Y2O3 nanoparticles has been achieved in YBa2Cu3O7−x (YBCO) films by metalorganic deposition using trifluoroacetates (TFA-MOD). The formation of integrated nanoparticles increases the critical current density (J c) of Y2O3/BZO doped-YBCO films while keeping the critical transition temperature (T c) close to that in the pure YBCO films. The YBCO film with 7.0mol.% BZO and 7.0mol.% Y2O3 showed T c value of 90K and J c value of 6.5mA/cm2 at self-field (0T, 77K). The strongly enhanced flux pinning over a wide range of magnetic field can be attributed to the combined different crystal structures of BZO and Y2O3 created by optimized TFA-MOD conditions. [Copyright &y& Elsevier]

Developing a rapid and continuous synthesis method for scalable production of upconversion nanoparticles (UCNPs) plays an important role in the applications of advanced color display, high-resolution biomedical imaging and precise optical thermometry. Here, for the first time, we report the multicolor tunable upconversion luminescence (UCL) in Y 2 O 3 :Yb3+/Er3+ (x/1 mol%) UCNPs with the average size of ∼14 nm, which were successfully fabricated by liquid-fed flame aerosol synthesis with a high production rate of ∼40 g h−1. Under the excitation of 980 nm continuous-wave (CW) laser, the UCL color can be efficiently modulated from green to red and the red-to-green (R/G) UCL intensity ratio is enhanced dramatically as the doping concentration of Yb3+ ions increases from 1 to 15 mol%. The UCL color manipulation can be ascribed to the cross-relaxation (CR) and the energy back transfer (EBT) processes between Yb3+ and Er3+ ions, and it was proved by investigating the dependence of UCL on the pump power and the decay lifetimes of 4S 3/2 and 4F 9/2 states. Moreover, the coefficients of CR and EBT processes were also calculated by a rate equation model, and the results suggest that they are efficient in Y 2 O 3 host. In addition, the optical thermal sensing performance was also evaluated by analyzing fluorescence intensity ratio (FIR) of the thermally coupled levels (2H 11/2 , 4S 3/2) of Er3+ ions in Y 2 O 3 :Yb3+/Er3+ (1/1 mol%) UCNPs, achieving an excellent thermal sensitivity of 0.0196 K−1 at 543 K. • Y 2 O 3 :Yb3+/Er3+ upconversion nanoparticles were fabricated by a self-built swirl-stabilized spray flame reactor. • The production rate reaches to a high value of 40 g h−1. • Intense and color-tunable emission from green to red can be acquired by adjusting the doping Yb3+concentration. An excellent thermal sensitivity of 0.0196 K−1 at 543 K was achieved in Y 2 O 3 :Yb3+/Er3+ (1/1 mol%) nanoparticles. [ABSTRACT FROM AUTHOR]