Electrical conductivity of Ag<Subscript>8</Subscript>SnS<Subscript>6</Subscript>-Ag<Subscript>2</Subscript>SnS<Subscript>3</Subscript>-AgBr alloys

The electrical conductivity of Ag₈SnS₆-[(AgBr)₄ · SnS₂] alloys in the Ag₈SnS₆-Ag₂SnS₃-AgBr system has been measured by a dc probe method between 210 and 380 K. The non-Arrhenius behavior of their conductivity is attributed to the fact that electrical and mass transport processes in these alloys involve both silver cations and bromide anions.     

Phase relations in the LaB<Subscript>6</Subscript>-MoB<Subscript>2</Subscript> system

LaB₆-MoB_2.2 alloys have been prepared at 2600°C in high-purity helium in a vacuum induction furnace. As found by microstructural analysis and x-ray diffraction, the components of this system form a eutectic. The microstructure of the eutectic has been studied. MoB_2.2 is shown to undergo a transformation during cooling, with the precipitation of submicron-sized Mo₂B₅ and α-MoB particles. For this reason, its microhardness increases with an increase in the melting temperature of the alloys because the diffusion rate rises with temperature.     

Directional solidification and growth characteristics of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Er<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>/ZrO<Subscript>2</Subscript> ternary eutectic ceramic by laser floating zone melting

Directionally solidified Al₂O₃/Er₃Al₅O₁₂/ZrO₂ ternary eutectic ceramic in situ composite rods with length of 110 mm have been fabricated by laser floating zone melting. The microstructural characteristics of steady growth zone, initial growth zone and solid/liquid interface are investigated under high temperature gradient. In the steady growth zone, the eutectic spacing (λ) is rapidly decreased as increasing the growth rate (V), and the corresponding relationship between growth rate and eutectic spacing is determined to be λ = 11.14 × V ^?1/2. The temperature gradient has been measured to be about 5.3 × 10³ K/cm. In the initial growth zone, the melting process and temperature distribution are recorded by infrared thermal imager, and several unstable complex microstructures are observed. In the quenched zone, the regular eutectics with minimum eutectic spacing of 200 nm are obtained. Moreover, the solid/liquid interface during solidification shows convex interface morphology and the interface height is gradually decreased as increasing the growth rate. The eutectic growth behaviors at the center and edge of the as-grown rod are compared and discussed.     

Lithium ion conductivity of LiLaO<Subscript>2</Subscript>-Li<Subscript>2</Subscript>ZrO<Subscript>3</Subscript> solid solutions

The limits of the LiLaO₂-and Li₂ZrO₃-based solid solutions in the LiLaO₂-Li₂ZrO₃ system have been determined: 0–10 mol % Li₂ZrO₃ and 0–5 mol % LiLaO₂, respectively. We have studied the transport properties (electronic conductivity, temperature and composition dependences of conductivity and activation energy) of lithium lanthanate and the solid solutions in the LiLaO₂-Li₂ZrO₃ system. Conduction in LiLaO₂ is likely due to lithium ion transport through a polyhedral network.     

Effect of cerium additive and secondary phase analysis on Ag<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> ceramics

Cerium-doped silver bismuth titanate—Ag_0.5Bi_0.5TiO₃ (ABT) ceramics have been synthesized by the high-temperature solid-state reaction method. The structure and elemental examination of the prepared ceramic was analysed by X-ray diffraction (XRD), Fourier transform infrared, scanning electron microscopy and energy-dispersive spectroscopy. XRD analysis showed the presence of pyrochlore structure and secondary phase when more than 5 mol% cerium was added. The impact of temperature on cerium-doped silver bismuth titanate samples was analysed by differential thermal analysis and differential scanning calorimetry. Cerium doping caused the flaky morphology comparing with undoped sample. The homogeneity of all the samples was discussed in detail by diffuse reflectance spectrum. This is the first time the reflection process is analysed for the cerium-doped ABT system to the best of our knowledge.     

Synthesis and microstructure of nanocrystalline Yb<Subscript>2</Subscript>O<Subscript>3</Subscript> powders

Nanocrystalline ytterbia powders have been synthesized using different precursors prepared by precipitation from nitrate solutions: ytterbium carbonates, oxalates, and hydroxides. The powders have been characterized by X-ray diffraction and scanning electron microscopy. The nature of the precursor has no effect on the crystallization temperature of ytterbia but influences its microstructure. The particles range in shape from spherical to platelike. The average crystallite size of the Yb₂O₃ powders is 20–25 nm. Raising the heat-treatment temperature from 600 to 1000°C increases the crystallite size to 33–46 nm. The highest thermal stability is offered by the ytterbia powders prepared through carbonate decomposition.     

Crystallization behaviour and mechanical properties of rapidly solidified Al<Subscript>87.5</Subscript>Ni<Subscript>7</Subscript>Mm<Subscript>5</Subscript>Fe<Subscript>0.5</Subscript> amorphous alloy

The crystallization behaviour and the mechanical properties of rapidly solidified Al_87.5Ni₇Mm₅Fe_0.5 alloy ribbons have been examined in both as-melt-spun and heat-treated condition using differential scanning calorimetry, X-ray diffractometry (XRD), transmission electron microscopy (TEM), tensile testing and Vicker’s microhardness machine. XRD and TEM studies revealed that the as-melt-spun ribbons are fully amorphous. The amorphous ribbon undergoes three-stage crystallization process upon heating. Primary crystallization resulted in the formation of fine nanocrystalline fcc-Al particles embedded in the amorphous matrix. The second and third crystallization stages correspond to the precipitation of Al₁₁(La,Ce)₃ and Al₃Ni phases, respectively. Microhardness and tensile strength of the ribbons were examined with the variation of temperature and subsequently correlated with the evolved structure. Initially, the microhardness of the ribbon increases with temperature followed by a sharp drop in hardness owing to the decomposition of amorphous matrix that leads to formation of intermetallic compounds     

Electrochemical properties of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/C and Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/C/Ag nanomaterials

We have prepared and characterized lithium titanate-based anode materials, Li₄Ti₅O₁₂/C and Li₄Ti₅O₁₂/C/Ag, using polyvinylidene fluoride as a carbon source. The formation of such materials has been shown to be accompanied by fluorination of the lithium titanate surface and the formation of a highly conductive carbon coating. The highest electrochemical capacity (175 mAh/g at a current density of 20 mA/g) is offered by the Li₄Ti₅O₁₂-based anode materials prepared using 5% polyvinylidene fluoride. The addition of silver nanoparticles ensures a further increase in electrical conductivity and better cycling stability of the materials at high current densities.     

Martensitic phase transformation in single crystal Co<Subscript>5</Subscript>Ni<Subscript>2</Subscript>Ga<Subscript>3</Subscript>

The magnetic, thermal, and transport properties of martensitic phase transformation in single crystal Co₅Ni₂Ga₃ have been investigated. The single crystal Co₅Ni₂Ga₃ shows martensitic transformation at 251 K on cooling and 254 K on warming. Large jumps in the temperature-dependent resistance curve, temperature-dependent magnetization curve, and temperature-dependent thermal conductivity curve are observed at martensitic transformation temperature (T _M). Negative magnetoresistance due to spin disorder scattering was observed in Co₅Ni₂Ga₃ single crystal at all temperature range. The temperature-dependent negative magnetoresistance shows a peak at T _M, which indicates that the spin disorder increases in the process of phase transition. Co₅Ni₂Ga₃ sample exhibits a temperature dependence of thermal conductivity κ(T) (dκ/dT > 0) due to electrons being above temperature 100 K.     

Structural and transport properties of the layered cuprate Pr<Subscript>2</Subscript>CuO<Subscript>4</Subscript>

The structural and transport properties of the layered cuprate Pr₂CuO₄ have been studied in the temperature range 300–2100 K using molecular dynamics simulation. The first evidence is presented for a premelting effect in Pr₂CuO₄: disordering on one of its oxygen sites and abnormally fast oxygen diffusion at temperatures above 1700 K. We have clarified the microscopic mechanism of oxygen ion transport in this material. The large oxygen diffusion coefficient (D > 10⁻⁷ cm²/s) obtained in our simulations of the layered cuprate Pr₂CuO₄ suggests that it has considerable potential as a host for electrode materials with mixed ionic-electronic conductivity.     

Electrical and thermodynamic properties of Cs<Subscript>0.97</Subscript> Rb<Subscript>0.03</Subscript>H<Subscript>2</Subscript>PO<Subscript>4</Subscript>

The transport properties of Cs_0.97Rb_0.03H₂PO₄ have been studied using polycrystalline samples and single crystals. The mixed salt is isostructural with cesium dihydrogen phosphate and has slightly smaller unitcell parameters. The cation substitution increases the low-temperature ionic conductivity of the material by about two orders of magnitude but has an insignificant effect on the conductivity of the high-temperature phase. The low-temperature conductivity of single-crystal samples exhibits significant anisotropy, with σ _a < σ _b±c . The conductivity of the polycrystalline material is close to σ _b±c . The substitution reduces the temperature of the superionic phase transition by 20°C and enhances the thermal stability of the high-temperature phase at low humidity (1 mol % H₂O).     

Extruded thermoelectric materials based on Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript> solid solutions

Extruded n-type materials based on Bi₂Te₃-Bi₂Se₃ alloys containing 6 to 40 mol % Bi₂Se₃ have been investigated using microstructural analysis and thermoelectric measurements at room temperature and in the range 100–400 K. Their electrical properties have been compared to those of single-crystal analogs. Compositions have been found at which the extruded materials offer the highest thermoelectric performance in different temperature ranges.     

Enhancement in electrical conductivity of Li<Subscript>2</Subscript>O: B<Subscript>2</Subscript>O<Subscript>3</Subscript>: V<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

The study of electrical conductivity of 30Li₂O: (70 − x) B₂O₃: xV₂O₅ glass samples has been carried out. The results have been explained by dividing the temperature range into two regions. In region I, conductivity shows Arrhenius behaviour for all the samples. The conductivity increases with addition of V₂O₅. The results have been explained in the light of Anderson and Stuart Model. In region II, an anomalous enhancement in the conductivity is observed for all the samples up to certain temperature beyond which the conductivity decreases. The enhancement in the conductivity in the annealed glass sample has been attributed to nanocrystallization.     

Magnetotransport effects in granular Cd<Subscript>3</Subscript>As<Subscript>2</Subscript> + MnAs structures at high pressures

The transport properties of granular Cd₃As₂ + MnAs (44.7% MnAs) composite structures have been studied near room temperature at high hydrostatic pressures of up to 9 GPa. The results demonstrate that the composite undergoes a structural phase transition and has a pressure-induced negative magnetoresistance.     

Phase equilibria in the La<Subscript>2</Subscript>O<Subscript>3</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>-Nb system and thermal stability of LaNb<Subscript>7</Subscript>O<Subscript>12</Subscript>

The phase equilibria in the ternary system La₂O₃-Nb₂O₅-Nb have been studied at subsolidus temperatures in vacuum (6.65 × 10^?3 Pa), and the temperature stability limits of LaNb₇O₁₂ have been determined in vacuum and during heating in air.     

Microstructure and Electrical Transport Properties of Bi<Subscript>3</Subscript>TiNbO<Subscript>9</Subscript> High-Temperature Piezoceramics

High-density ceramic samples of the Bi₃TiNbO₉ ferroelectric phase with a layered perovskite-like structure have been produced by tape casting slurry technology and hot pressing processes. The samples have been characterized by X-ray diffraction and dielectric, piezoelectric, and pyroelectric measurements. The results demonstrate that the samples have a well-defined texture due to the preferential orientation of the basal planes of their platelike grains across the pressing axis or along the film casting direction. The Curie temperature of the samples has been determined to be T_C = 1180 K. The samples have anisotropic electrical transport characteristics. Their piezoelectric constants d₃₃ in directions perpendicular and parallel to the texture plane is 22 and 5 pC/N, respectively. The conclusion has been drawn that the synthesized materials are potentially attractive for producing high-temperature piezoelectric elements.     

Superconducting Properties of NdO<Subscript>0.5</Subscript><Emphasis Type="Bold">F</Emphasis><Subscript>0.5</Subscript>BiS<Subscript>2</Subscript> Single Crystals

We report on superconducting properties of high-quality single crystals of F-substituted NdOBiS₂ using low-temperature magnetization and transport measurements. Using the mixture of CsCl and KCl as the flux, we have synthesized our single crystals. This compound exhibits bulk superconductivity with a transition temperature of about T _c～4.6 K. The critical current density J _c as a function of temperature has been derived and decreases with the increasing temperature. We construct the phase diagram H _c2(T). The zero-temperature value for \(H_{\mathrm {c2}}^{B\parallel c}\) for value for \(T_{c}^{90~\%}\) and \(T_{c}^{0~\%}\) is estimated to be approximately 2.17 and 1.72 T respectively by using Werthamer-Helfand-Hohenberg model.     

Structural,dielectric and electrical properties of CaBa<Subscript>4</Subscript>SmTi<Subscript>3</Subscript>Nb<Subscript>7</Subscript>O<Subscript>30</Subscript> ferroelectric ceramic

The polycrystalline sample of CaBa₄SmTi₃Nb₇O₃₀, a member of tungsten bronze family, was prepared by solid-state reaction method. X-ray diffraction analysis shows the formation of single-phase compound with an orthorhombic structure at room temperature. Scanning electron micrograph of the material shows uniform distribution of grains. Detailed studies of dielectric properties of the compound as a function of temperature at different frequencies suggest that the compound has a dielectric anomaly of ferroelectric to paraelectric type at 198°C, and exhibits non-relaxor kind of diffuse phase transition. The ferroelectric nature of the compound has been confirmed by recording polarization-electric field hysteresis loop. Piezoelectric and pyroelectric studies of the compound have been discussed in this paper. Electrical properties of the material have been analyzed using complex impedance technique. The Nyquist plots manifest the contribution of grain boundaries (at higher temperature), in addition to granular contribution (at all temperatures) to the overall impedance. The temperature dependence of dc conductivity suggests that the compound has negative temperature coefficient of resistance (NTCR) behaviour. The frequency dependence of ac conductivity is found to obey Jonscher’s universal power law. The observed properties have been compared with calcium free Ba₅SmTi₃Nb₇O₃₀ compound.     

A facile method to improve the high rate capability of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanowire array electrodes

The capability of fast charge and fast discharge is highly desirable for the electrode materials used in supercapacitors and lithium ion batteries. In this article, we report a simple strategy to considerably improve the high rate capability of Co₃O₄ nanowire array electrodes by uniformly loading Ag nanoparticles onto the surfaces of the Co₃O₄ nanowires via the silver-mirror reaction. The highly electrically conductive silver nanoparticles function as a network for the facile transport of electrons between the current collectors (Ti substrates) and the Co₃O₄ active materials. High capacity as well as remarkable rate capability has been achieved through this simple approach. Such novel Co₃O₄-Ag composite nanowire array electrodes have great potential for practical applications in pseudo-type supercapacitors as well as in lithium ion batteries.     

Magnetic and Electrical Properties Induced by the Substitution of Divalent by Monovalent in the La<Subscript>0.6</Subscript>Ca<Subscript>0.4</Subscript>MnO<Subscript>3</Subscript> Compound

The La_0.6Ca_0.4?x Ag _x MnO₃ samples with x = 0 and 0.10 were prepared by sol–gel methods. Structural and electrical measurements were performed to examine the effect of the silver substitution in the calcium sites on the physical properties. Magnetization versus temperature studies have shown that all samples exhibit a magnetic transition from ferromagnetic to paramagnetic phase when temperature is increased. The second transition in the resistivity in the La_0.6Ca_0.4MnO₃ compound can be attributed to an abnormality characteristic of charge ordering (CO) effect. The electrical resistivity was described by a phenomenological percolation model. Ten percent of Ag substitution in the Ca site exhibits a magnetoresistance value about 75 % near room temperature at the applied magnetic field of 8 T.