Microdeformations of the crystal lattice of PbTe1 − x Br x solid solutions

Microdeformations of the crystal lattice of PbTe_{1 ? x} Br _x solid solutions depending on the bromine content are determined by analysis of the physical broadening of X-ray reflections. It is found that they increase with the introduction of bromine from 0.188% (for undoped PbTe) to 0.283% for PbTe_{1 ? x} Br _x at x = 0.02. The microstrains remain constant with a further increase in the bromine content.     

Photoluminescence spectra of Cd x Hg1 − x Te quantum-well heterostructures

Photoluminescence spectra are measured for a nanoscale Cd _x Hg_{1 ? x} Te heterostructure with a single quantum well about 12.5 nm thick in the case x = 0.24. The confined energy levels and the respective rates of different optical transitions are calculated on this basis. Major radiative processes are identified.     

Structure and properties of Cd x Hg1−x Te-metal contacts

A metal-semiconductor contact is a composite structure consisting of several nanodimensional layers. The contact properties depend strongly on the technique of metal deposition. A metal forms chemical compounds with the components of Cd _x Hg_1?x Te (CMT), thus changing the properties of the surface layer. Mercury is accumulated at the interface with the metal, while tellurium is accumulated on the metal surface. The CMT compounds with metals, heats of their formation, and the Fermi level shifts are reported. The structure and properties of the interfaces between CMT and gold, silver, indium, aluminum, copper, and other metals, as well as the effect of sublayers of other metals and insulators, are described.     

Mechanism of local amorphization of a heavily doped Ti1 − x V x CoSb intermetallic semiconductor

Structural and electron transport characteristics of a TiCoSb intermetallic semiconductor heavily doped with the V donor impurity (dopant concentration ～9.5 × 10¹⁹ ? 1.9 × 10²¹ cm^?3, temperatures 80–380 K) have been investigated and the distribution of the electron density of states in this material has been calculated. Different occupancies have been established for Co and (Ti, V) atomic positions in the Ti_{1 ? x} V _x CoSb lattice; this difference is equivalent to introduction of two types of acceptors into the semiconductor. Suppression of the metallic conductivity in the n-type semiconductor with an increase in the donor concentration has been found, which is explained by simultaneous generation of acceptors. It is shown that the methods of numerical calculation adequately describe the physical processes if the occupancy of unit-cell positions is taken into account in construction of the Wigner-Seitz lattice. The results obtained are discussed within the model of a heavily doped and compensated Shklovskii-Efros semiconductor.     

Effect of Fe Substitution on Thermoelectric Properties of Fe x In4−x Se3 Compounds

Starting from elemental powder mixtures of Fe _x In_4?x Se₃ (x = 0, 0.05, 0.1, 0.15), polycrystalline In₄Se₃-based compounds with homogeneous microstructures were prepared by mechanical alloying (MA) and hot pressing (HP). With the increase of x from 0 to 0.15, the electrical resistivity and the absolute value of the Seebeck coefficient increased, while the thermal conductivity first decreased and then increased. The maximal dimensionless figure of merit ZT of 0.44 was obtained for the Fe _x In_4?x Se₃ (x = 0.05) sample at 723 K.     

Inelastic electron scattering cross-section spectroscopy of Ge x Si1 − x nanoheterostructures

Two-component Ge _x Si_{1 ? x} (0 ≤ x ≤ 1) structures are studied by electron spectroscopy. The atomic composition of the structures is determined from X-ray photoelectron spectroscopy data. The reflection electron-energy-loss spectra for a series of samples with different x at primary-electron energies from 200 to 3000 eV are recorded. Using the experimental spectra, the electron energy loss dependences of the product of the electron inelastic mean free path and the differential inelastic electron scattering cross section are calculated. It is shown that the quantitative characteristics of these dependences can be used to determine the atomic concentrations of elements in the investigated system.     

Improved Thermoelectric Properties of Se-Doped n-Type PbTe1−x Se x (0 ≤ x ≤ 1)

Enhancement of the thermoelectric figure of merit is of prime importance for any thermoelectric material. Lead telluride has received attention as a potential thermoelectric material. In this work, the effect of Se substitution has been systematically investigated in PbTe_1?x Se _x . The thermoelectric properties of synthesized alloys were measured in the temperature range of 300 K to 873 K. For the particular composition of x = 0.5, α was highest at ~292 μV/K, while k was lowest at ~0.75 W/m-K, resulting in the highest dimensionless figure of merit of ZT ≈ 0.95 at 600 K. The increase in thermopower for x = 0.5 can be attributed to the high distortion in the crystal lattice which leads to the formation of defect states. These defect states scatter the majority charge carriers, leading to high thermopower and high electrical resistivity. The dramatic reduction of the thermal conductivity for x = 0.5 can be attributed to phonon scattering by defect states.     

Polarized photoluminescence of nc-Si–SiO x nanostructures

The effect of photoluminescence polarization memory in nc-Si–SiO _x light-emitting structures containing Si nanoparticles (nc-Si) in an oxide matrix is for the first time studied. The polarization properties of continuous and porous nanostructures passivated in HF vapors (or solutions) are studied. It is established that the polarization memory effect is manifested only after treatment of the structures in HF. The effect is also accompanied by a shift of the photoluminescence peak to shorter wavelengths and by a substantial increase in the photoluminescence intensity. It is found that, in anisotropic nc-Si–SiO _x samples produced by oblique deposition in vacuum, the degree of linear photoluminescence polarization in the sample plane exhibits a noticeable orientation dependence and correlates with the orientation of SiO _x nanocolumns forming the structure of the porous layer. These effects are attributed to the transformation of symmetrically shaped Si nanoparticles into asymmetric elongated nc-Si particles upon etching in HF. In continuous layers, nc-Si particles are oriented randomly, whereas in porous structures, their preferential orientation coincides with the orientation of oxide nanocolumns.     

Solid-State Synthesis and Thermoelectric Properties of Mg2Si1−x Sn x

Mg₂Si_1?x Sn _x (0 ≤ x ≤ 1) solid solutions have been successfully prepared by mechanical alloying and hot pressing as a solid-state synthesis route. All specimens were identified as phases with antifluorite structure. The electrical conduction changed from n-type to p-type at room temperature for x ≥ 0.5 due to the intrinsic properties of Mg₂Sn. The absolute value of the Seebeck coefficient decreased with increasing temperature, and the electrical conductivity increased with increasing temperature; this is indicative of nondegenerate semiconducting behavior. The thermal conductivity was reduced by Mg₂Si-Mg₂Sn solid solution due to phonon scattering by the alloying effect.     

Effects of Cooling Rate and Composition on Mechanical Properties of Directionally Solidified Pb100?x -Sn x Solders

Pb_100?x -Sn _x solders (x = 5 wt.%, 10 wt.%, 20 wt.%, 35 wt.%, 50 wt.%, 60 wt.%, 61.9 wt.%, and 95 wt.%) were directionally solidified upward over a wide range of cooling rates $ \dot{T} $ (0.016 K s^?1 to 4.0 K s^?1) by using a Bridgman-type directional solidification furnace. Microstructure parameters (primary dendrite arm spacing, ?? ₁, and eutectic spacing, ?? _E) and mechanical properties (microhardness, HV, and ultimate tensile strength, ??) of the Pb_100?x -Sn _x alloys were measured. The dependences of the microhardness and ultimate tensile strength on the cooling rate, microstructure parameters, and composition were determined. According to experimental results, the microhardness and ultimate tensile strength of the solidified samples increase with increasing cooling rate and Sn content, but decrease with increasing microstructure parameters.     

Thermoelectric Properties of Light-Element-Containing Zintl Compounds CaZn2−x Cu x P2 and CaMnZn1−x Cu x P2 (x = 0.0–0.2)

Light-element-containing CaAl₂Si₂-type Zintl phases CaZn_2?x Cu _x P₂ and CaMnZn_1?x Cu _x P₂ (x = 0.0–0.2) have been synthesized by solid-state reaction. Electrical resistivity (ρ), Seebeck coefficient (α), and thermal conductivity (κ) were measured over a wide temperature (T) range (80–1000 K) to evaluate the thermoelectric potential of these materials. Below 300 K, the power factor (PF; α ²/ρ) is very small. Above 600 K, however, PF increases rapidly for all compositions because of a rapid increase of α and a simultaneous decrease of ρ. The measured large α is consistent with the wider band gap expected for these compositions. Compared with the pure compounds, larger PF values are observed for the Cu-substituted compounds; the largest observed PF is ～0.5 mW/m K². The thermal conductivity is found to be rather low, despite the presence of light elements, and is in the range 1.0–1.5 W/m K at 1000 K. Because of the combination of low κ and moderate PF values, the dimensionless figure of merit ZT = α ² T/ρκ reaches a maximum of 0.4 for CaZn_1.9Cu_0.1P₂.     

Effect of annealing on the electrical properties of Pb1 − x Mn x Te single crystals with excess tellurium

The electrical conductivity σ, Hall coefficients R, and thermopower α of Pb_0.96Mn_0.04Te (Te) single crystals annealed at 573 K for 120 h are investigated. It is shown that, in contrast to unannealed samples, the investigated samples exhibit n-type conductivity and metal-type dependences σ(T) in the temperature range 77–300 K. It is suggested that, upon annealing, a portion of the excess tellurium atoms occupy vacancies in the lead sublattice with the formation of new vacancies in the tellurium sublattice of the samples.     

Crystal Structure and Physical Properties of Skutterudites SrPd4Sn x Sb12−x

A Pd-based skutterudite phase SrPd₄Sn _x Sb_12?x in which the 8c sites of the structure are occupied solely by Pd atoms and with a homogeneity range of 4.3(2) ≤ x ≤ 5.8(2) (wavelength dispersive x-ray spectroscopy) has been synthesized by solid-state reaction then spark-plasma sintering (SPS). It crystallizes as the filled-skutterudite structure type, electronically compensated by substitution of Sn for Sb at framework (24g) positions. The unit cell decreases substantially with increasing nominal and detected Sn content. Magnetization, specific heat, Hall effect, electrical resistivity, thermopower, and thermal conductivity were measured for the SPS-treated samples. SrPd₄Sn _x Sb_12?x is a diamagnetic material. Depending on composition it occurs in the metallic or semiconducting states. Hall effect data show that the type and concentration of most of the carriers depend on the Sn/Sb atomic ratio. The thermal conductivity of SrPd₄Sn _x Sb_12?x is approximately 3.0–5.0 W K^?1 m^?1 at 300 K. The Seebeck coefficient is negative throughout the temperature range covered, reaching approximately ?20 μV K^?1 at 300 K.     

Width of the excitonic absorption line in Al x Ga1 − x as alloys

Experimental data on the width of the absorption line corresponding to the exciton ground state in high-quality samples of Al _x Ga_{1 ? x} As (x = 0.15) quasi-binary alloy, obtained by Seisyan et al. (2005), are analyzed. The line corresponding to the 1s state is divided into separate components taking into account strain-induced splitting; Lorentzian- and Gaussian-shape contributions to the absorption curve; and overlap with the continuum absorption band, which broadens with increasing temperature. Analysis of the integrated absorption, relying on the fact that the temperature dependence of the absorption is typical of exciton polaritons in media possessing spatial dispersion, was carried out with the following parameters: critical value of the dissipation damping of the exciton Γ_c = 0.32 meV and maximum value of the absorption coefficient K _max = 89.5 eV/cm. This analysis makes it possible to determine the homogeneous component of the line broadening, which, up to the critical temperature T _c = 155 K does not exceed 0.2 meV. It is found that the “natural” width of the 1s-exciton line does not exceed 2.6 meV at T = 1.7 K, which is in agreement with theoretical estimates. At T = 1.7–60 K, the inhomogeneous broadening of the exciton peak related to the exciton scattering and localization by fluctuations of the alloy composition exceeds contributions related to phonons and ionized impurities by more than an order of magnitude and is dominant, but does not affect the integrated absorption by excitonic polaritons.     

Evidence of the third (A +) level of the mercury vacancy in Cd x Hg1 ? x Te

The existence of a previously unknown shallow acceptor level (depth of ??1 meV), which belongs to the intrinsic defect of the semiconductor crystal rather than to the impurity, is found for Cd _x Hg_{1 ? x} Te compounds. It is concluded from analysis of the experimental data that this state is the third level of the mercury vacancy V _Hg, which emerges due to the capture of an additional hole (state A ⁺).