Ionic conductivity of Li x Na1 − x Ta y Nb1 − y O3 solid solutions

Experimental data demonstrate that Li _x Na_{1 ? y} Ta _y Nb_{1 ? y} O₃ (y ≠ 0) ferroelectric solid solutions near special concentration points (x = 0.125 and 0.25), which have increased degrees of short- and long-range order, undergo a superionic transition. In the Raman spectra of Li_0.12Na_0.88Ta _y Nb_{1 ? y} O₃, the superionic transition shows up as a predominant “melting” of the alkali metal sublattice and broadening of the corresponding lines into a Rayleigh line wing, whereas the other sublattices in the structure remain relatively “rigid.” The temperature of the superionic transition can be tuned by varying the degree of static disorder of structural units in the Nb⁵⁺/Ta⁵⁺ sublattice.     

Edge absorption and light propagation in single crystals of Zn1−x Cd x As2 solid solutions

The transmittance of Zn_1?x Cd _x As₂ anisotropic single crystals in their transparency region is found to depend on the incident light polarization, photon energy, and sample thickness. This effect is shown to be associated with light scattering in Zn_1?x Cd _x As₂, which can be understood in terms of the crystal structure of the monoclinic crystals. The fundamental absorption edge in Zn_1?x Cd _x As₂ is dominated by an indirect forbidden transition for the E ‖ c polarization and by a direct forbidden transition for E ⊥ c.     

Modeling the concentration profiles of aluminum and indium impurities in crystals of germanium–silicon solid solutions

A one-dimensional problem of the axial distribution of Al and In impurities in uniform crystals of Ge–Si solid solutions grown by double feeding of the melt method has been solved in the Pfann approximation. The mathematical modeling results suggest that the impurity concentration profile in Ge–Si crystals of constant composition can be varied in a wide range through appropriate changes in the relationship between the crystal growth rate and the rates of feeding the melt using germanium and silicon rods. We demonstrate the possibility of growing completely homogeneous Ge–Si kAl,Inl crystals, in terms of both the concentrations of their major components and the impurity concentration profile.     

Electronic conductivity of Sr3-3xLa2x█x(VO4)2 solid solutions

The electronic conductivity of Sr_3-3xLa_2x█_x(VO₄)₂ solid solutions was measured at oxygen pressures from 10^-13 to 10⁵ Pa and temperatures from 1070 to 1270 K, and their band gap was determined as a function of composition. The activation energy (≏2.85 eV) and enthalpies of electron generation (≏4.2 eV) and migration (≏0.75 eV) were determined. A correlation between the band gap and electronic conductivity of the solid solutions was revealed     

Interdiffusion inα solid solutions of the Cu-Zn-Sn system

The interdiffusion coefficients in the f c c phase of Cu-Zn-Sn alloys, , have been determined at 1073 K. The concentration profiles indicate that the diffusion rate of tin is greater than that of zinc in the Cu-Zn-Sn alloy. The diffusion paths show the typical S-shaped curves. All of the four interdiffusion coefficients are positive and they are very sensitive to the solute concentration. The atomic mobilities of the three diffusing elements in Kirkendall planes increase in the order of Cu, Zn, Sn. The interaction energy of the Cu-Sn bond is much larger than that of the Zn-Sn bond. From the results of the present work it seems that the Onsager reciprocal relation holds in the a phase of the Cu-Zn-Sn system.     

Photoinduced electric properties of Pb1−xSnxTe single crystals

It was established that the simultaneous action of laser IR radiation (ω < E_g, where E_g, is the band gap) and an external field (density of current through the crystal, j≲10²A/cm²) results in an accelerated change in electrical properties of Pb_1−xSn_xTe single crystals, which is attributed to an accelerated diffusion in the external electric field of metallic ions from associates of metal-enriched defects and dopants, arising during the crystal growth.     

Thermoelectric properties of Bi2Te3-Sb2Te3 single crystals in the range 100–700 K

The electrical conductivity, thermoelectric power, and thermal conductivity of Bi₂Te₃-Sb₂Te₃ crystals grown by the floating-crucible technique were measured in the temperature range from 100 to 700 K. The thermoelectric figure of merit of the crystals was evaluated. The effect of crystal composition on these properties was analyzed.     

Temperature dependence of the pseudogap in Y1−zPrzBa2Cu3O7−δ single crystals

We investigate the conductivity in the basis plane of Y_1?zPr_zBa₂Cu₃O_7?δ and YBa₂Cu₃O_7?δ single crystals. The excess conductivity, Δσ, is described by Δσ ~ (1 ? T/T*)exp(Δ_ab*/T) in a wide temperature range T_f < T < T*, where T* is the mean field temperature of the superconducting transition. We determine that the temperature dependence of the pseudogap (PG) is described in terms of the BCS-BEC crossover theoretical model. It is observed that a reduction in the praseodymium content results to the widening of the temperature interval that the PG region is realized and a narrowing of the area of existence of the linear dependence of the resistivity, ρ(T), in the ab plane.     

Anisotropy of the non-equilibrium quasiparticle dynamics in single crystals of YBa2Cu3O7−δ

We report for the first time, measurements of ultrafast transients from YBCO in which the contributions from a- and b-axis response are separately identified using polarised light. A new signal is observed for Ea which has been obscured in all previous thin film experiments. Comparing the two contributions we find the new signal to be sensitive to T _c whilst the signal for Eb exhibits pseudogap behaviour.     

Giant dielectric properties of nanocrystalline Pb1−xSnxF2 solid solutions

Nanocrystalline Pb_1?xSn_xF₂ (x = 0.2, 0.3) solid solutions have been synthesized by mechanochemical milling at room temperature with grain size as small as 26 nm. These fluoride ion conducting materials exhibit giant values of the dielectric constant of ?′ > 10⁵ that is independent of temperature and frequency over wide ranges. The giant values of ?′ are suggested to be due to internal effects in the materials. The dielectric response has been analyzed by appropriate equivalent circuit representing the grain and internal effects in the materials. Interestingly, the dielectric constant of the current samples is found to be larger for the samples with smaller grain size, a behavior that is quite opposite to what usually observed in giant dielectric oxide materials, where ?′ is enhanced with substantial growth of the grain size. The possible origin of the giant dielectric constant is discussed in the present study.     

The AgxCu1−xInS2 solid solutions with 0≤x≤1

The phase equilibriums in the AgInS2–CuInS2 system were investigated by means of X-ray diffraction and differential thermal analysis and the AgInS2 and CuInS2 ternary compounds and the AgxCu1–xInS2 solid solutions were grown by two-zone horizontal method with the following directed crystallization of melt. The T–x phase diagram of this system was constructed and the formation of solid solutions in the complete range of compositions was discovered. The composition dependencies of microhardness, transmission spectra in the range of the fundamental absorption, infrared transmission spectra in the range from 150 to 400 cm-1 for the AgxCu1–xInS2 solid solutions were investigated. It was discovered that the composition dependence of microhardness is expressed by smooth curve having maximum for x=0.2. The composition dependencies of band gap have been analytically expressed at 77 and 293 K for the Ec and Ec direction of polarization and have non-linear behaviour. From the studies of the infrared transmission spectra the frequencies of optical phonons were determined and it was discovered that their composition dependence shows single mode behaviour.     

Study on the temperature dependence of the OH− absorption band in Hf-doped LiNbO3 crystals

We study in this paper the temperature dependence of the OH^? absorption band in LiNbO₃ crystals with different Hf-doping concentrations. It is found that the shoulder at 3500 cm^?1 appears in the doping level of 2.6 mol%, becomes more evident at 3 and 4 mol%, and then gradually faints when the doping concentration increases. This result is explained by the non-monotonic change of Nb vacancy density in the three stages of the defect evolution involved in the Hf incorporation of LN lattice. Moreover, the absorption difference analysis of the OH^? bands is consistent with this explanation and reveals that the mobility of H⁺ ions may be reduced by the strong trapping of the highly electronegative Nb vacancies.     

Effect of mechanical activation on the synthesis of α-Fe2O3-Cr2O3 solid solutions

Continuous -Fe₂O₃-Cr₂O₃ solid solution series have been synthesized by two methods: (i) direct heating of coprecipitated hydroxides, and (ii) mechanical pre-treatment followed by heating. It is shown that mechanical treatment leads to a decrease in the preparation temperature of the solid solutions to 623 K. The formation of a continuous solid solution series by direct heating begins only at 773 K. The formation of the solid solutions was established by X-ray diffraction analysis, infrared and Mössbauer spectroscopy. The decrease in synthesis temperature of the -Fe₂O₃-Cr₂O₃ solid solutions is attributed to activation of the samples during their mechanical treatment. The samples obtained have large specific surface areas (up to 130 m² g^–1).     

Analysis of the OH− binding energy in lithium niobate crystals

In this paper we present some new results on the behavior of OH centers in Mg doped lithium niobate samples in concentration just above the optical damage threshold. We studied how new hydrogen (protons) incorporate to the crystal distributing in different OH centers, and how some of these centers are preferentially destroyed when the hydrogen is extracted from the crystal. We conclude that in highly Mg doped LiNbO₃ crystals hydrogen tends to bound to oxygen ions located close to Mg_Nb defects having a stronger binding energy than unperturbed OH centers. The energy difference is about 0.25 eV. When each Mg_Nb defect has a close OH center, the remaining hydrogen forms unperturbed OH centers. Our results are compared with some recently published data.     

Enhancement of thermoelectric power in layered Bi2Sr2Co2−x Ir x O y single crystals

We report on the structural, electrical, and thermal transport properties of the single crystals of Bi₂Sr₂Co_2?x Ir _x O _y (0 ≤ x ≤ 0.2). Large-sized (centimeter-level) and good-quality single crystals were grown by a modified flux method. The substitution of Ir ions for Co ones makes the in-plane resistivity ρ _ab increase monotonically, whereas, the in-plane thermopower S _ab initially increases and then decreases as x is larger than 0.1. Therefore, among all samples, the in-plane power factor P _ab (=S _ab ² /ρ _ab) of Bi₂Sr₂Co_1.9Ir_0.1O _y would reach a maximum value of 116.4 μWm^?1K^?2 at 300 K and shows a significant improvement of about 20 % compared to that of the parent sample. Our results indicate that an appropriate doping of Ir ions at Co-sites may provide an effective way to enhance the thermoelectric performance of Bi₂Sr₂Co₂O _y system.     

The growth and properties of (Sbx Bi1–x)2Te3 crystals

Abstract

Vertical Bridgman systems with programmable temperature control are used to grow (Sb_xBi_1:x)₂Te₃ crystals. High purity Bi, Sb and Te are used as sources and the diameter of 1.1 cm, little soft bulk crystals of (Sb_xBi_1–x)₂ Te₃ can be obtained. Scanning electron microscope (SEM) and electron probe microanalysis (EPMA) are used to analyze the micro‐structure and the compositions of the crystal. From the X‐ray diffraction patterns it appears that the grown crystal is single crystal or directive polycrystal. If the uniformity of the source solution and grown temperature are under control, then the high quality of single crystals can be obtained. The dependence of crystal structure and the thermoelectric characteristics on the changed compositions of grown crystals are discussed. The optimum composition for the thermoelectric properties is Sb_1.00 Bi_1.04Te_2.96. When the DC current, 3A, is applied to the Sb_1.00 Bi_1.04 Te_2.96 crystal with suitable electrodes, the temperature difference (△T) between two sides of the crystal can be as high as 60°C. It is 2 times larger than that ever obtained by Sb₂Te₃ crystal. It appeared that the grown (Sb_xBi_1‐x)₂Te₃ crystals have the potential on the fabrication of thermoelectric devices and electronic cooling system.     

Structural investigation and sonophotocatalytic properties of the solid solutions Sr(Mo1−xWx)O4 crystals synthesized by the sonochemical method

Journal of Materials Science: Materials in Electronics - In this paper, the solid solutions of strontium molybdate-tungstate [Sr(Mo1?xWx)O4] crystals with (x?=?0, 0.25, 0.50,...     

Thermal conductivity of single crystals of M1−x M x ′F2 (M = Ca, Sr; M′ = Mn, Co) isovalent solid solutions

The thermal conductivity of single crystals of the Ca_0.99Co_0.01F₂, Ca_0.97Co_0.03F₂, Sr_0.99Mn_0.01F₂, Sr_0.989Mn_0.01Co_0.001F₂, and Sr_0.995Co_0.005F₂ solid solutions has been measured in the temperature range 50–300 K. The results demonstrate that doping of CaF₂ and SrF₂ crystals with small amounts of isovalent transition metal impurities is accompanied by a significant reduction in thermal conductivity.     

Synthesis and properties of TlIn1 − x Gd x Se2 solid solutions

This paper describes the synthesis and crystal growth of TlIn_{1 − x} Gd _x Se₂ solid solutions and presents the T-x phase diagram of the TlInSe₂-TlGdSe₂ system. Partial gadolinium substitution for indium in TlInSe₂ increases the microhardness and unit-cell parameters of the material and reduces its band gap. According to X-ray diffraction data for TlInSe₂-TlGdSe₂ crystals, the TlIn_{1 − x} Gd _x Se₂ (0 < x ≤ 0.1) solid solutions crystallize in tetragonal symmetry and are isostructural with TlInSe₂.