Photoacoustic spectroscopy of thin films of As<Subscript>2</Subscript>S<Subscript>3</Subscript>, As<Subscript>2</Subscript>Se<Subscript>3</Subscript> and GeSe<Subscript>2</Subscript>

Photoacoustic spectroscopy (PAS) is one of the important branches of spectroscopy, which enables one to detect light-induced heat production following the absorption of pulsed radiation by the sample. As₂S₃, As₂Se₃ and GeSe₂ exhibit a wide variety of photo-induced phenomena that enable them to be used as optical imaging or storage medium and various electronic devices, including electro-optic information storage devices and optical mass memories. Therefore, accurate measurement of thermal properties of semiconducting films is necessary to study the memory density. The thermal conductivity of thin films of As₂S₃ (thickness 100 μm and 80 μm), As₂Se₃ (thickness 100 μm and 80 μm) and GeSe₂ (thickness 120 μm and 100 μm) has been measured using PAS technique. Our result shows that the thermal conductivity of thicker films is larger than the thinner films. This can be explained by the thermal resistance effect between the film and the surface of the substrate.      

Thermal conductivity of Na<Subscript>2</Subscript>W<Subscript>2</Subscript>O<Subscript>7</Subscript> crystal

The thermal conductivity of Na₂W₂O₇ single crystal has been studied along the main crystallographic directions at temperatures of 50–573 K. A low thermal conductivity is found to correlate with a significant difference in the cation weight.     

Effect of thermal strain on structure and polarization fatigue of CSD-derived PbZr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>O<Subscript>3</Subscript>/LaNiO<Subscript>3</Subscript> hetero-structures

PbZr_0.53Ti_0.47O₃/LaNiO₃ (PZT/LNO) hetero-structures have been successfully deposited on MgO, SrTiO₃, Al₂O₃ and Si substrate by chemical solution routes, respectively. The X-ray diffraction measurements show that out-of-plane lattice parameters of PZT increase as increase of thermal expansion coefficient of substrate. Polarization fatigues of Pt/PZT/LNO capacitors are strongly affected by the thermal strain caused by difference of thermal expansion coefficient between PZT and substrate materials. High fatigue resistance of Pt/PZT/LNO can be obtained by using substrate with similar thermal expansion coefficient as PZT. PACS 77.84.Dy; 78.20.Ci; 81.20.Fw     

X-ray study of [N(CH<Subscript>3</Subscript>)<Subscript>4</Subscript>]<Subscript>2</Subscript>ZnCl<Subscript>4</Subscript> at low temperatures

The unit cell parameters a, b, and c of [N(CH₃)₄]₂ZnCl₄ have been measured by x-ray diffraction in the temperature range 80–293 K. Temperature dependences of the thermal expansion coefficients α_a, α_b, and α_c along the principal crystallographic axes and of the unit cell thermal expansion coefficient α_V were determined. It is shown that the a=f(T), b=f(T), and c=f(T) curves exhibit anomalies in the form of jumps at phase transition temperatures T₁=161 K and T₂=181 K and that the phase transition occurring at T₃=276 K manifests itself in the a=f(T) and b=f(T) curves as a break. A slight anisotropy in the coefficient of thermal expansion of the crystal was revealed. The phase transitions occurring at T₁=161 K and T₂=181 K in [N(CH₃)₄]₂ZnCl₄ were established to be first-order.     

Thermal sensors based on Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript> and (Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>)<Subscript>70</Subscript>(Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>)<Subscript>30</Subscript> thin films

Thin films of Sb₂Te₃ and (Sb₂Te₃)₇₀(Bi₂Te₃)₃₀ alloy and have been deposited on precleaned glass substrate by thermal evaporation technique in a vacuum of 2?×?10^?6 Torr. The structural study was carried out by X-ray diffractometer, which shows that the films are polycrystalline in nature. The grain size, microstrain and dislocation density were determined. The Seebeck coefficient was determined as the ratio of the potential difference across the films to the temperature difference. The power factor for the (Sb₂Te₃)₇₀ (Bi₂Te₃)₃₀ and (Sb₂Te₃) is found to be 19.602 and 1.066 of the film of thickness 1,500 Å, respectively. The Van der-Pauw technique was used to measure the Hall coefficient at room temperature. The carrier concentration was calculated and the results were discussed.     

Mechanism of thermal decomposition of K<Subscript>2</Subscript>FeO<Subscript>4</Subscript> and BaFeO<Subscript>4</Subscript>: A review

This paper presents thermal decomposition of potassium ferrate(VI) (K₂FeO₄) and barium ferrate(VI) (BaFeO₄) in air and nitrogen atmosphere. Mössbauer spectroscopy and nuclear forward scattering (NFS) synchrotron radiation approaches are reviewed to advance understanding of electron-transfer processes involved in reduction of ferrate(VI) to Fe(III) phases. Direct evidences of Fe ^V and Fe ^IV as intermediate iron species using the applied techniques are given. Thermal decomposition of K₂FeO₄ involved Fe ^V, Fe ^IV, and K₃FeO₃ as intermediate species while BaFeO₃ (i.e. Fe ^IV) was the only intermediate species during the decomposition of BaFeO₄. Nature of ferrite species, formed as final Fe(III) species, of thermal decomposition of K₂FeO₄ and BaFeO₄ under different conditions are evaluated. Steps of the mechanisms of thermal decomposition of ferrate(VI), which reasonably explained experimental observations of applied approaches in conjunction with thermal and surface techniques, are summarized.     

Thermal conductivity of the PbGeO<Subscript>3</Subscript> and PbGe<Subscript>3</Subscript>O<Subscript>7</Subscript> glasses

This paper reports on a study of the thermal conductivity of the PbGeO₃ and PbGe₃O₇ glasses.     

The Composition of Intermediate Products of the Thermal Decomposition of (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>ZrF<Subscript>6</Subscript> to ZrO<Subscript>2</Subscript> from Vibrational-Spectroscopy Data

Thermal decomposition of (NH₄)₂ZrF₆ resulting in ZrO₂ formation within the temperature range of 20°–750°С has been investigated by means of thermal and X-ray diffraction analysis and IR and Raman spectroscopy. It has been established that thermolysis proceeds in six stages. The vibrational-spectroscopy data for the intermediate products of thermal decomposition have been obtained, systematized, and summarized.     

Enhanced electrochemical properties and thermal stability of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> by surface modification with Eu<Subscript>2</Subscript>O<Subscript>3</Subscript>

Layered LiNi_1/3Co_1/3Mn_1/3O₂ cathode material is synthesized via a sol-gel method and subsequently surface-modified with Eu₂O₃ layer by a wet chemical process. The effect of Eu₂O₃ coating on the electrochemical performances and thermal stability of LiNi_1/3Co_1/3Mn_1/3O₂@Eu₂O₃ cells is investigated systematically by the charge/discharge testing, cyclic voltammograms, AC impedance spectroscopy, and DSC measurements, respectively. In comparison, the Eu₂O₃-coated sample demonstrates better electrochemical performances and thermal stability than that of the pristine one. After 100 cycles at 1C, the Eu₂O₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ cathode demonstrates stable cyclability with capacity retention of 92.9 %, which is higher than that (75.5 %) of the pristine one in voltage range 3.0–4.6 V. Analysis from the electrochemical measurements reveals that the remarkably improved performances of the surface-modified composites are mainly ascribed to the presence of Eu₂O₃-coating layer, which could efficiently suppress the undesirable side reaction and increasing impedance, and enhance the structural stability of active material.     

Computer calculations for thermal behavior of Na<Subscript>2</Subscript>CO<Subscript>3</Subscript>-Li<Subscript>2</Subscript>CO<Subscript>3</Subscript> melt

The thermal behavior of Na₂CO₃+Li₂CO₃ melt is studied by the method of thermodynamic simulation. The equilibrium compositions of the gas and salt phases are calculated at different temperatures in the initial argon atmosphere. Basic trends of the variation in the compositions of the melts and the gas phase above the melts in the presence of carbon are determined. The obtained results characterizing the stability of carbonate components in the melt are analyzed.     

Spectral-luminescent investigations of glasses and glass-ceramic materials in Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-GeO<Subscript>2</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Glasses of 2Bi₂O₃-3GeO₂-xFe₂O₃ composition, where x = 0–1.5, are obtained under oxidizing and reducing conditions. Glass-ceramic materials are produced by the thermal treatment of the glasses, the properties of which, as well as those of the original glasses, are studied by the methods of X-ray phase analysis and optical and luminescent spectroscopy. It is found that the Fe³⁺/Fe²⁺ ion ratio in the samples changes depending on the synthesis conditions of the original glasses and crystallization process.     

Phase transitions in the (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>NbOF<Subscript>5</Subscript> oxyfluoride

The thermal and dielectric properties of the (NH₄)₂NbOF₅ oxyfluoride have been investigated. It has been established that the structural phase transitions Cmc2₁ → C2 → Ia observed at the temperatures T ₁ = 258.0 K and T ₂ = 218.9 K exhibit a nonferroelectric nature. The hydrostatic pressure, which stabilizes the initial phase and destabilizes the low-temperature phase, hardly affects the temperature range of stability of the intermediate phase. The model of sequential ordering of the structural elements due to phase transitions has been analyzed using experimental data on the entropies of the phase transitions.     

The Debye temperature and Grüneisen parameter of the CaLa<Subscript>2</Subscript>S<Subscript>4</Subscript>-La<Subscript>2</Subscript>S<Subscript>3</Subscript> system

The thermal expansion coefficient of solid solutions in the CaLa₂S₄-La₂S₃ system at a temperature of 300 K is investigated experimentally. The Debye temperature, the Grüneisen parameter, and the isothermal compressibility coefficient of solid solutions in the system under investigation are determined from the experimental thermal expansion coefficient. It is demonstrated that, upon substitution of calcium ions for cation vacancies in La₂S₃, the Debye temperature decreases, the isothermal compressibility coefficient increases, and the Grüneisen parameter remains constant for all compositions in the CaLa₂S₄-La₂S₃ system. A correlation between the ionic radii of Ca²⁺ and La³⁺, the concentration of cation vacancies, and the rigidity of the lattice, on the one hand, and the Debye temperature, the Grüneisen parameter, and the isothermal compressibility coefficient, on the other, is revealed for the studied samples.     

Low-temperature thermal-expansion anomaly in Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript>CuO<Subscript>6</Subscript>

Single-crystal samples of the Bi_{2 + x}Sr_{2 ? x ? y}Cu_{1 + y}O_{6 + δ} system revealed anomalous (negative) thermal expansion in the temperature range 10–20 K. Magnetic fields of 1–3 T were found to strongly affect the position and width of the anomaly region. A thermal-expansion singularity was detected at temperatures T≈30–50 K, which may be related to the formation of a pseudogap.     

Synthesis,thermal and electrical behavior of the superprotonic conductor phase in Rb<Subscript>3</Subscript>(HSeO<Subscript>4</Subscript>)<Subscript>2.5</Subscript>(H<Subscript>2</Subscript>PO<Subscript>4</Subscript>)<Subscript>0.5</Subscript> compound

The Rb₃(HSeO₄)_2.5(H₂PO₄)_0.5 compound was prepared and its thermal behavior and electric properties were investigated. The thermogravimetry (TGA) analysis and the differential scanning calorimetric (DSC) show the presence of a structural phase transition of the title compounds at 374 K which is confirmed by the variation of fp and σ_dc as a function of temperature. The complex impedance of the Rb₃(HSeO₄)_2.5(H₂PO₄)_0.5 compound has been investigated in the temperature range of 295–453 K and in the frequency range 209 Hz–1 MHz. The impedance plots show semicircle arcs at different temperatures, and an electrical equivalent circuit has been proposed to explain the impedance results. The circuits consist of the parallel combination of bulk resistance Rp and constant phase elements CPE₁ in series with fractal capacity CPE₂. The frequency dependence of the conductivity is interpreted in terms of Jonscher’s law. The conductivity dc follows the Arrhenius relation. The near value of activation energies obtained from the analysis of modulus, conductivity data, and circuit equivalent confirm that the transport is through the ion hopping mechanism, dominated by the motion of the H⁺ proton in the structure of the investigated materials.     

Thermal properties and ionic conductivity of Li<Subscript>1,3</Subscript>Ti<Subscript>1,7</Subscript>Al<Subscript>0,3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> solid electrolytes sintered by field-assisted sintering

Li_1,3Ti_0,7Al_0,3(PO₄)₃ (LATP) powder was obtained by a conventional melt-quenching method and consolidated by field-assisted sintering technology (FAST) at different temperatures. Using this technique, the samples could be sintered to relative densities in the range of 93 to 99 % depending on the sintering conditions. Ionic and thermal conductivity were measured and the results are discussed under consideration of XRD and SEM analyses. Thermal conductivity values of 2 W/mK and ionic conductivities of 4?×?10^?4 Scm^?1 at room temperature were obtained using relatively large particles and a sintering temperature of 1000 °C at an applied uniaxial pressure of 50 MPa.     

Conductivity and spectroscopic studies of Li<Subscript>2</Subscript>O-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

Lithium vanadium-borate glasses with the composition of 0.3Li₂O–(0.7-x)B₂O₃–xV₂O₅ (x?=?0.3, 0.325, 0.35, 0.375, 0.4, 0.425, 0.45, and 0.475) were prepared by melt-quenching method. According to differential scanning calorimetry data, vanadium oxide acts as both glass former and glass modifier, since the thermal stability of glasses decreases with an increase in V₂O₅ concentration. Fourier transform infrared spectroscopy data show that the vibrations of [VO₄] structural units occur at V₂O₅ concentration of 45 mol%. It is established that the concentration of V⁴⁺ ions increases exponentially with the growth of vanadium oxide concentration. Direct and alternative current measurements are carried out to estimate the contribution both electronic and ionic conductivities to the value of total conductivity. It is shown that the electronic conductivity is predominant in the total one. The glass having the composition of 0.3Li₂O-0.275B₂O₃-0.475V₂O₅ shows the highest electrical conductivity that has the value of 7.4?×?10^?5 S cm^?1 at room temperature.     

Ferroelectric phase transition of Nb-doped Bi<Subscript>3.25</Subscript>La<Subscript>0.75</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> ceramics

Bi_3.25La_0.75Ti_3-yNb_yO₁₂ (y=0.0, 0.03, 0.09, 0.15, 0.21) were synthesized using the solid-state reaction method. The effects of Nb doping on ferroelectric properties were studied through dielectric and P-E measurements. The value of P_r increases with increasing Nb content. Bi_3.25La_0.75Ti_3-yNb_yO₁₂ ceramics exhibit a maximum remanent polarization of P_r=27 μC/cm² at an Nb content of y=0.09. These results indicate that Nb doping can improve the ferroelectric properties of BLT ceramics. The Curie temperature, T_c, decreased with increasing Nb-content, and the ferroelectric phase transition of BLTNy is a second-order transition without thermal hysteresis. PACS 77.55.+f; 77.80.-e; 77.22.Jp     

Structural disordering in Cr-doped Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> spinels

The processes of lithium redistribution in the structure of cubic Li₄Ti₅O₁₂ spinel, caused by both chromium doping and thermal activation, have been investigated by nuclear magnetic resonance. It is shown that Li ions migrate from tetra- to octahedral crystallographic positions with an increase in temperature. This process becomes more pronounced at temperatures above 400 K. In contrast, the fraction of tetrahedrally coordinated Li increases as a result of doping with chromium.     

Negative thermal expansion coefficient in the high-temperature superconductor Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript>CaCu<Subscript>2</Subscript>O<Subscript>8 + <Emphasis Type="Italic">x</Emphasis></Subscript>

Powder and single-crystal samples of the high-temperature superconductor Bi₂Sr₂CaCu₂O_{8 + x} are studied by X-ray diffraction. Its thermal expansion coefficient is found to be negative over a wide temperature range (160–260 K). Possible causes of this effect are discussed.