Growth of the (In2S3)x(FeIn2S4)1 ? x single crystals and properties of photoelectric structures on their basis

Complete mutual solubility in the (In₂S₃) _x (FeIn₂S₄)_{1 − x} system is established. The technology is developed, and single crystals of the continuous series of the (In₂S₃) _x (FeIn₂S₄)_{1 − x} solid solutions are grown for the first time. The linear dependence of the unit cell parameter of single crystals with a cubic spinel lattice on the solid solution composition is found. First, photosensitive Schottky barriers are fabricated, and then, based on studies of their photosensitivity, the character of band-to-band transition is discussed and the values of the band gap depending on the atomic composition are estimated. The possibility of using the obtained solid solutions as broadband photoconverters of optical radiation is revealed.     

Discovery of the (In2S3)x(MnIn2S4)1 ? x solid solutions and fabrication of photosensitive structures based on them

A technology of growing single crystals of (In₂S₃) _x (MnIn₂S₄)_{1 − x} solid solutions that provides control over their atomic composition in the entire concentration range 0 ≤ x ≤ 1 is developed. It is shown that, in the range x = 0–1, the single crystals have the cubic spinel structure and the unit cell parameter a follows the linear dependence on x. The exponential character of the temperature dependence of resistivity of solid solutions, on which the first photosensitive Cu/(In₂S₃)x(MnIn₂S₄)_{1 − x} structures are obtained, is revealed. The first photosensitivity spectra of these structures are obtained, and, based on these spectra, dependences of energy of the direct and indirect band-to-band transitions on the composition x are determined. The possibility of applying these structures in broad-band photoconverters of optical radiation is concluded.     

Synthesis,Structure and Electrical Properties of(SnO2)x(In2O3)1?x(x=0.5–1) Nanocomposites

The experimental results of synthesizing thin films (<1 μm thick) of (SnO₂) _x (In₂O₃)_{1 − x} (x = 0.5–1 wt) nanocomposites fabricated by high-frequency magnetron sputtering of metal-oxide targets in a controlled Ar + O₂ atmosphere are presented. The films, deposited on hot substrates (400°C), are studied by the X-ray diffraction analysis, atomic-force microscopy, and optical and electrical methods. The effect of the synthesis conditions and film composition on the size of crystalline grains, band gap, and the concentration and mobility of free charge carriers was determined. It is shown that films of the composition (SnO₂) _x (In₂O₃)_{1 − x} with x = 0.9 are the most promising for applications in gas sensorics.     

I–V characteristic of p-n structures based on a continuous solid solutions (Si2)1 ? xx(CdS)x

The I–V characteristics of the p-Si-n-(Si₂) _{1 − x} (CdS) _x (0 ≤ x ≤ 0.01) structures are investigated at various temperatures. It is found that the I–V characteristic of such structures has a sublinear portion of the current growth with voltage V ≈ V ₀exp(JaW). The experimental results can be explained on the basis of the theory of the injection depletion effect. It is shown that the mobility of the minority carrier (hole) decreases with an increasing temperature. Original Russian Text ? A.S. Saidov, A.Yu. Leyderman, Sh.N. Usmonov, K.T. Kholikov, 2009, published in Fizika i Tekhnika Poluprovodnikov, 2009, Vol. 43, No. 4, pp. 436–438.     

Properties and structure of (As2Se3)1 ? z (SnSe2) z ? x (Tl2Se) x and (As2Se3)1 ? z (SnSe) z ? x (Tl2Se) x glasses

Tin is stabilized in the bivalent and tetravalent states in the structure of (As₂Se₃)_{1 − z} (SnSe₂) _{z − x} (Tl₂Se) _x and (As₂Se₃)_{1 − z} (SnSe) _{z − x} (Tl₂Se) _x glasses. The presence of bivalent tin in the structural network of a glass does not give rise to extrinsic conductivity. Dependences of density, microhardness, and the glass-transition temperature on the composition of the glasses are interpreted using a model according to which the structure of the glasses is composed of structural units that correspond to As₂Se₃, AsSe, TlAsSe₂, Tl₂Se, SnSe, and SnSe₂ compounds. Original Russian Text ? G.A. Bordovsky, A.V. Marchenko, E I. Terukov, P.P. Seregin, T.V. Likhodeeva, 2008, published in Fizika i Tekhnika Poluprovodnikov, 2008, Vol. 42, No. 11, pp. 1353–1356.     

Effects of Zn/Mg Ratio on the Microstructure and Microwave Dielectric Properties of (Zn1?xMgx)2SiO4 Ceramics

Ceramics of nominal composition (Zn_1−x Mg _x )₂SiO₄ were synthesized by the solid-state method. The phase evolution, microstructure, and microwave dielectric characteristics of the (Zn_1−x Mg _x )₂SiO₄ (0 < x < 1.0) ceramics were investigated systematically. The sintering range was widened and the densification temperatures of the present ceramics were much lower compared with the Zn₂SiO₄ and Mg₂SiO₄ end-members. Coexistence of Mg₂SiO₄ and Zn₂SiO₄ phases was observed in the (Zn_1−x Mg _x )₂SiO₄ ceramics with x = 0.4 and 0.6. The MgSiO₃ secondary phase was also observed due to Mg substitution. Changes in grain shapes from equiaxed to rectangular were observed in sintered samples as x varied from 0.7 to 1.0. The microwave characteristics of (Zn_1−x Mg _x )₂SiO₄ ceramics were significantly improved by the suppression of the MgSiO₃ phase, where an enhanced quality factor (Qf) value was obtained. The best microwave characteristics were achieved in the (Zn_1−x Mg _x )₂SiO₄ ceramic with Zn/Mg ratio of 1.5 sintered at 1250°C: ε _r = 6.2, Qf = 148,740 GHz, τ _f = −54.2 ppm/°C.     

Magnetic susceptibility of (Bi2 ? xSbx)Te3 (0 < x < 1) alloys in the temperature range 2 to 50 K

The superconducting quantum interferometer device with Josephson junctions (SQUID magnetometer) is used to study the temperature dependences of the magnetic susceptibility of (Bi_2−x Sb _x )Te₃ (0 < x < 1) alloy crystals in the temperature range 2 to 50 K, at the magnetic field vector H orientations H | C ₃ and H ⊥ C ₃ with respect to the crystal trigonal axis C ₃. It is found that the magnetic susceptibility of the ion core of the samples under study is χ ^G = −0.35 × 10⁻⁶ cm³/g, the contribution of lattice defects to magnetic susceptibility can be disregarded, and the contribution of free carriers is of a diamagnetic nature in the entire studied temperature range. It is shown that the contribution of free carriers to the resulting magnetic susceptibility and its anisotropy can be described within the Pauli and Landau-Peierls approach. In calculating the magnetic susceptibility, taking into account the constant concentration of free carriers in the state of pronounced degeneracy, it is found that the temperature dependence of the anisotropic effective masses varies with crystal chemical composition. This is possibly associated with the complex structure of the valence band and its variation as the Sb₂Te₃ content in the alloy increases.     

Thermoelectric Properties of Tix(HfyZr1?y)1?xNiSn0.998Sb0.002 Half-Heusler Ribbons

Ribbons of Ti _x (Hf _y Zr_1−y )_1−x NiSn_1−z Sb _z (x = 0.1 to 1, y = 0.1 to 0.9, z = 0, 0.002, 0.004) were prepared by spin casting and annealed for 1 h at T _a = 1000 K, 1050 K, 1073 K, and 1100 K. The crystal phase of the ribbons was investigated by x-ray diffraction analysis and transmission electron microscopy. All the ribbons consisted of a phase with a half-Heusler structure. The Seebeck coefficient, electrical conductivity, thermal conductivity, power factor, and figure of merit ZT at room temperature were clarified experimentally as a function of x, y, z, and T _a. Despite the large thermal conductivity, the power factor and figure of merit were remarkably large at x = 0.5, y = 0.5, z = 0.002, and T _a = 1073 K, because the Seebeck coefficient and electrical conductivity were large.     

Thermoelectric Properties of Ag-Doped n-Type (Bi2?xAgxTe3)0.96?(Bi2Se3)0.04 Pseudobinary Alloys

n-Type thermoelectric powders of (Bi_2−x Ag _x Te₃)_0.96−(Bi₂Se₃)_0.04 (0 ≤ x ≤ 0.05) have been synthesized by mechanical alloying and then consolidated by spark plasma sintering. The analysis results show that the grain size of pure Bi, Te, Ag, and Se powders is decreased to about 1 μm to 0.5 μm after they are mechanically alloyed for 2 h. The power factor of bulk material increases with increasing Ag-doping content, while the trend for the lattice thermal conductivity is the opposite. Bulk (Bi_0.99Ag_0.04)₂(Te_0.96Se_0.04)₃ after milling for 12 h exhibits a higher power factor, lower thermal conductivity, and thus a higher ZT of 0.74 at 373 K.     

Single-Crystal Investigations on Quaternary Clathrates Ba8Cu5SixGe41?x (x?=?6, 18, 41)

Type I clathrates have been considered as promising thermoelectric materials due to their special structural characteristics: the “rattling” guest atoms in the larger of the two cages of the clathrate I structure are frequently held responsible for the low lattice thermal conductivity. By single-crystal x-ray diffraction, we investigated the quaternary clathrates Ba₈Cu₅Si _x Ge_41−x (x = 6, 18, 41). Rietveld refinements confirmed that the clathrates in this system crystallize with cubic primitive symmetry, in the type I clathrate structure, and that no phase transitions occur in the temperature range investigated (100 K to 300 K). We derive the concentration dependencies of the Debye temperature, the Einstein temperatures, the static disorder parameters, and the size of the two cages and argue that these dependencies underpin the previously assumed different bonding character of the Ba guest atoms in the larger and smaller cages. The linear thermal expansion coefficients for the samples are derived.     

Optical properties of quantum-confined heterostructures based on GaPxNyAs1 ? x ? y alloys

The results of calculations of the band gap in GaP _x N _y As_{1 − x − y} alloys and the estimated parameter of hybridization of the conduction band in GaP and the localized level of nitrogen are reported. The optical properties of quantum-confined heterostructures based on GaP _x N _y As_{1 − x − y} alloys synthesized on the GaP (100) substrate surface are studied by photoluminescence measurements in the temperature range of 15–300 K. The heterostructures consist of GaP_0.814N_0.006As_0.18 quantum wells separated by GaP barrier layers. The well width and the barrier thickness are 5 nm. Heterostructures with different numbers of periods are considered. On optical excitation of the structures, an intense photoluminescence line is observed in the spectral range 620–650 nm. The photoluminescence spectra of the GaP_0.814N_0.006As_0.18/GaP quantum wells are profoundly broadened because of the inhomogeneity of the quaternary alloy in composition. It is established that the increase in the number of quantum well layers from 10 to 25 does not results in degradation of the photoluminescence properties of the heterostructures. The results of the study support the view that it is possible to produce efficient optoelectronic devices on the basis of GaP _x N _y As_{1 − x − y} alloys.     

Pulsed Electroplating: a Derivate Form of Electrodeposition for Improvement of (Bi1?xSbx)2Te3 Thin Films

Bismuth antimony telluride (Bi_1−x Sb _x )₂Te₃ thermoelectric compounds were synthesized by pulse plating. Due to the large number of parameters available (pulse waveform, on/off pulse time, applied current density), this advanced form of electrodeposition allows better control of the interfacial supply and electrochemical reactions and offers effective ways to improve macroscopic properties such as adhesion and to produce crack-free hard deposits and fine-grained films with higher uniformity and lower porosity. The influence of pulse parameters (pulse time t _on, cathodic current density J _c) on the stoichiometry, roughness, and crystallography of deposits was studied. The thermoelectric properties (electrical resistivity and Seebeck coefficient) of the films were measured. The results revealed that deposits have p-type conductivity directly after electroplating (Seebeck coefficient around 150 μV K⁻¹), in contrast to films synthesized by direct current, which require annealing. An improvement of resistivity was observed: for a direct-current-deposited film the resistivity is around 5000 μΩ m, whereas for a pulse-deposited film the resistivity was around 200 μΩ m.     

Improved Thermoelectric Properties of (GeTe)90(AgySb2?yTe3?y)10 by Tuning the Ag-to-Sb Ratio

(GeTe)₉₀(Ag _y Sb_2−y Te_3−y )₁₀ (y = 0.6, 0.7, 0.8, 1.0) compounds were prepared by combining melting and hot pressing, and the thermoelectric properties were studied over the temperature range of 300 K to 770 K. Powder x-ray diffraction results revealed that all the samples were the rhombohedral phase with space group R3m. The electrical conductivity of samples decreased with temperature, while the Seebeck coefficient increased. The thermal conductivity of all the samples was very low, especially for those with the lower y values. High ZT values above 1.6 were obtained for the samples with y = 0.6, 0.7, and 0.8.     

Optical properties of quaternary GaNxAsyP1 ? x ? y semiconductor alloys

The optical properties of quaternary GaN _x As _y P_{1 − x − y} semiconductor alloys grown on a GaP (100) substrate surface are studied by photoluminescence spectroscopy in the temperature range 20–300 K and by photoluminescence excitation spectroscopy at liquid-nitrogen temperature. The measurements are carried out for the GaN _x As _y P_{1 − x − y} alloys, for which the nitrogen and arsenic molar fractions x and y range from 0.006 to 0.012 and from 0.00 to 0.18, respectively. A comparative analysis of the data is conducted, and the dependences of the energy position of the photoluminescence peak on the composition of the quaternary alloy are established. From the studies of photoluminescence in the range 20–300 K, it is found that the temperature dependence of the position of the photoluminescence peak substantially differs from the behavior described by Varshni’s expression.     

Pb(Zn1/3Nb2/3)0.2(Hf1-xTix)0.8O3陶瓷压电能量收集特性研究

采用铌铁矿前驱体两步法制备了Pb(Zn_1/3Nb_2/3)_0.2(Hf_1-xTi_x)_0.8O₃(PZNH_1-xT_x)钙钛矿压电陶瓷,研究了铪钛比对陶瓷相结构、电学性能和能量收集特性的影响。结果表明,当x=0.52时,陶瓷样品位于准同型相界,具有最优综合压电性能：居里温度T_C=287 ℃,品质因数FOM≈14 753×10^-15 m²/N,压电电荷常数d₃₃=492 pC/N。由该组成材料构建的悬臂梁型压电能量收集器输出功率密度高达4.16 μW/mm³,所转化的电能可成功点亮138盏并联的LED灯。结果表明,PZNHT陶瓷在压电能量收集领域具有良好的应用潜力。     

Influence of Cadmium Composition on CH4–H2-Based Inductively Coupled Plasma Etching of Hg1?xCdxTe

In this paper, inductively coupled plasma etching of Hg_1−x Cd _x Te in CH₄–H₂-based chemistry is studied. This work is focused on the effects of substrate temperature, ion energy, and alloy composition on etch rate and surface composition. A strong influence of substrate temperature is shown. The etch rate is multiplied by more than a factor of 3 when the temperature is increased from 5°C to 35°C. A purely physical Cd removal mechanism is ruled out using x-ray photoelectron spectroscopy data from samples etched at different temperatures. Under the conditions of very low ion energy, an etching mechanism limited by the supply of active species from the plasma predicts an Hg_1−x Cd _x Te etch rate evolution that fits very well with our data.     

Electronic and Optical Properties of MgxZn1?xO and BexZn1?xO Quantum Wells

As a preparatory step toward establishing reliable numerical design tools for ZnO-based optoelectronic devices, we have reassessed the available information on material parameters relevant for the simulation of light-emitting diodes (LEDs) with active regions including ZnO, MgZnO, and BeZnO layers. The impact of different approximations for the electronic structure and the interface polarization charge on the optical properties of bulk ZnO and ZnO/MgZnO quantum wells has been evaluated, and a consistent set of parameters has been used not only for systematic comparison of ZnO/MgZnO and ZnO/BeZnO single quantum well structures but also for the first simulation of a realistic ZnO/BeZnO multiple quantum well LED.     

Transport and Thermoelectric Properties of the Ca1?xSrxRu1?yMnyO3 System

The magnetic, transport, and thermoelectric properties of Ca_1−x Sr _x Ru_1−y Mn _y O₃ have been investigated. Ferromagnetism with relatively high T _C (>200 K) was introduced by Mn doping. In particular, ferromagnetism appeared in the Ca_0.5Sr_0.5Ru_1−y Mn _y O₃ system at y > 0.2. The maximum T _C (=270 K) was recorded for a specimen of Ca_0.5Sr_0.5Ru_0.4Mn_0.6O₃. The ferromagnetism seems to be due to the mixed-valence states of Mn³⁺, Mn⁴⁺, Ru⁴⁺, and Ru⁵⁺ ions. The metallic character of Ru-rich specimens was suppressed by Mn substitution, and the system was transformed into a semiconductor at relatively low Mn content near y = 0.1. Specimens with higher Mn content (y > 0.8) had large thermoelectric power (50 μV K⁻¹ to 130 μV K⁻¹ at 280 K) accompanied by relatively low resistivity (0.03 Ω cm to 1 Ω cm). The Ca_0.5Sr_0.5Ru_1−y Mn _y O₃ system seems to have good potential as a thermoelectric material for use above 300 K.     

(Ba1−xNax)F(Zn1−xMnx)Sb: A novel fluoride-antimonide magnetic semiconductor with decoupled charge and spin doping

We report the successful synthesis and characterization of a novel 1111-type magnetic semiconductor (Ba_1−xNa_x)F(Zn_1−xMn_x)Sb (0.05 ≤ x ≤ 0.175) with tetragonal ZrSiCuAs-type structure, which is isostructural to the layered iron-based superconductor La(O,F)FeAs. Na substitutions for Ba and Mn substitutions for Zn introduce carriers and local magnetic moments, respectively. Ferromagnetic interaction is formed when Na and Mn are codoped, demonstrating that local magnetic moments are mediated by carriers. Iso-thermal magnetization shows that the coercive field is as large as ~ 12 000 Oe, which is also reflected in the large split between the temperature-dependent magnetization in zero-field-cooling and field-cooling condition. AC susceptibility under zero field demonstrates that samples evolve into spin-glass state below spin freezing temperature T_f. The measurements of temperature-dependent resistivity indicate that (Ba_1−xNa_x)F(Zn_1−xMn_x)Sb exhibits semiconducting behaviour.     

Structure and High-Temperature Thermoelectric Properties of the n-Type Layered Oxide Ca2?xBix?δMnO4?γ

We have investigated the effects of Bi doping on the crystal structure and high-temperature thermoelectric properties of the n-type layered oxide Ca₂MnO_4−γ . The electrical conductivity σ and the absolute value of the Seebeck coefficient S were, respectively, found to increase and decrease with Bi doping. The thermal conductivity κ of doped Ca₂MnO_4−γ is relatively low, 0.5 W/m K to 1.8 W/m K (27°C to 827°C). Consequently, the ZT value, ZT = σS ² T/κ, increases with Bi doping. The maximum ZT is 0.023 for Ca_1.6Bi_0.18MnO_4−γ at 877°C, which is ten times higher than that of the end member, Ca₂MnO_4−γ . The increase of ZT mainly results from the considerable increase of σ, which can be explained in terms of structural change. The␣Mn-O(1) and the Mn-O(2) distances in the c-direction and ab-plane, respectively, increase with increasing Bi concentration, indicating that the valence state of Mn ions decreases with the increase of electron carriers in the CaMnO₃ layers. In addition, the Mn-O(2)-Mn bond angle increases linearly with Bi doping, leading to an improvement of the electron carrier mobility.