Anomalous Hall Effect in Sn1−x−y Mn x Eu y Te and Sn1−x−y Mn x Er y Te Mixed Crystals

The Anomalous Hall Effect (AHE) was investigated in IV–VI ferromagnetic semimagnetic semiconductors of Sn_1?x Mn _x Te codoped with either Eu or Er. The analysis of experimental data is as follows. Hall resistivity and magnetization showed that AHE coefficient R _s depends on temperature and its value decreases with thetemperature increase. We observe that above ferromagnet–paramagnet transition temperature R _s changes sign. We discuss the possible physical mechanisms responsible for observed temperature dependence of R _s , particularly change of the sign.     

Magnetic, optical, and kinetic properties of Hg1 − x − y Mn x Dy y Te crystals

We have studied the magnetic, optical, and kinetic properties of Hg_{1 ? x ? y} Mn _x Dy _y Te crystals. The behavior of their magnetic susceptibility can be accounted for by the presence of clusters of various sizes. The Hg_{1 ? x ? y} Mn _x Dy _y Te crystals are shown to be n-type. Absorption data are used to determine the optical band gap of the crystals.     

Al y In1 – y Sb1 – x Bi x /InSb Photodetecting Superlattices

The conditions are examined for the formation of Al _y In_{1 – y} Sb_{1 – x} Bi _x solid solutions on InSb substrates. The grown heterostructures are potentially attractive as the basis for the next generation of optoelectronic devices—superlattice-based avalanche photodiodes.     

Properties of Phase-Separated, Super-Oxygenated La2−x Sr x CuO4+y

We review a series of experiments that have established that super-oxygenated La_2−x Sr _x CuO_4+y phase-separates at low temperature into large magnetic and superconducting regions, driven by the physics of the doped holes themselves. Magnetization studies of trapped flux indicate that the large phase-separated magnetic and superconducting regions develop from nanoscale regions of charge inhomogeneity present in Sr-doped La₂CuO₄ and other more commonly studied cuprates. Neutron studies of the elastic magnetic diffraction show that the peak intensity grows with applied field as in La_2−x Sr _x CuO₄. However, the magnitude of the increase varies widely and is not well accounted for by current theory.     

Thermpower of Ce x Y1−x InCu2 and CeInCu y Ag2−y

The temperature dependence of the thermoelectric power (TEP) of the solid solutions Ce _x Y_1–x InCu₂ and CeInCu _y Ag_2–y was measured between 1.2 and 300 K. The substitution of Y for Ce shows the Kondo origin of the giant TEP peak in CeInCu₂. Furthermore, the replacement of Cu by Ag allows us to follow both the spin interaction and Kondo terms, which, according to Ref. 1, characterize the TEP of heavy fermion compounds.     

Preparation of nanostructured TiC x O y

Nonstoichiometric titanium oxycarbide, TiC _x O _y , nanopowder consisting of isolated stable nanoparticles with an average size of 40 ± 10 nm has been prepared by two-step synthesis from metallic titanium and oxalic acid. The nanostructured precipitate obtained by reacting titanium and oxalic acid was reduced by carbon in the process of solid-state sintering in vacuum. We examine the capabilities of this approach, which allows one to control the average particle size and composition of titanium oxycarbide.     

Structure, Phonon Vibration, and Spin Correlation of LaBa2Cu3−x Co x O y

Polycrystalline samples LaBa₂Cu_3?xCo _x O _y (0 ≤ x ≤ 1.0) were synthesized by solid state reaction method. The structure, phonon vibration, conduction, and spin correlation were investigated by means of X-ray diffraction, infrared spectra, resistivity, and electron spin resonance. It is found that there are orthorhombic–tetragonal and tetragonal–orthorhombic structural transitions with Co doping, and the conduction behavior changes from metallic to semiconducting. With the increase of Co content, the Cu(1)—O(1) phonon mode around 531 cm^?1 softens, the Cu(2)—O(2) phonon mode around 657 cm^?1 hardens, and the Cu(1)—O(4) mode around 583 cm^?1 is nearly unchanged. The Cu²⁺ spins tend to localize with Co doping. The changes in structure, phonon vibration, and spin correlation with Co doping are analyzed and discussed.     

Composition and predominant electron scattering mechanisms in Hg1 − x − y Cd x Eu y Se crystals

The surface of Hg_{1 ? x ? y} Cd _x Eu _y Se crystals has been examined by electron microscopy using backscattered and secondary electron imaging, and the composition of the crystals has been determined. Using transport and optical measurements, we have identified the predominant electron scattering mechanisms in the Hg_{1 ? x ? y} Cd _x Eu _y Se crystals.     

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.     

Synthesis of Li x Na1 − x Ta y Nb1 − y O3 and LiTa y Nb1 − y O3 perovskite and pseudoilmenite solid solutions

This paper compares the solid-state reactions underlying the synthesis of LiTa _y Nb_{1 ? y} O₃ and Li _x Na_{1 ? x} Ta _y Nb_{1 ? y} O₃ solid solutions with the use of Ta_2y Nb_{2(1 ? y)}O₅ niobium tantalum pentoxides and a mechanical mixture of the Ta₂O₅ and Nb₂O₅ pentoxides. Our results demonstrate that the synthesis with the use of Ta_2y Nb_{2(1 ? y)}O₅ allows phase-pure solid solutions to be obtained at substantially lower temperatures in comparison with a mechanical mixture of Ta₂O₅ and Nb₂O₅.     

Structures and properties of La1−x,Sr x CoO3−y,prepared by freeze drying

Several samples of La_1–x Sr _x CoO_3–y (x = 1, 0.8, 0.5, 0.2) were prepared by calcining freezedried, stoichiometric mixtures of nitrates at different temperatures and for different lengths of time. Selected samples were characterized by powder X-ray diffraction, conductivity measurements, Brunauer-Emmett-Teller surface area measurement, and by electrochemical cyclic voltammetry in alkaline solutions and alkaline solutions containing methanol. The structures of each composition were complex and varied with composition and preparation conditions. There is evidence for non-stoichiometry caused by oxygen anion vacancies. For La_0.5Sr_0.5CoO_3–y the electrochemical activity towards the oxidation of methanol is a maximum at the fully formed cubic perovskite. The oxidation currents at La_0.8Sr_0.2CoO_3–y and La_0.2Sr_0.8CoO_3–y go through maxima at more distorted structures.     

Study of transport properties of Ge50− x Sb y Te100+ x − y thin film alloy

The transport properties of Ge_50−xSb_yTe_100+x−y Alloys where 0 ≤ x ≤ 15 and 0 ≤ y ≤ 30 in the thin films state were studied. The temperature dependence of the d.c. electrical conductivity measurements for all prepared composition with different thickness, shows that, all samples behaves as a semiconductor up to a specific temperature at which an abrupt transition appears. That transition is due to the change of the semiconductor from non-degenerate to degenerate state. The temperature dependence of a.c. electrical conductivity measurements shows that, the a.c. conductivity for all films are frequency independent in the tested frequency range from 0.12 to 10 kHz. Thermoelectric power was found to have positive sign indicating that these alloys are p-type semiconductors. The value of temperature coefficient γ was found to be in the order of 10⁻⁴ (eV/K). The calculation of the free-charge carrier concentration and charge mobility shows that, the abrupt transition appears in thermoelectric power and conductivity are due to an abrupt increase in the mobility.     

Self-propagating high-temperature synthesis of SrTiO3 and Sr x Ba y TiO3 (x+y=1)

Thermal initiation of mixed powders of SrO₂ and titanium and/or TiE (E = O₂, Cl₃) induces a self-propagating reaction. Trituration of the product with water yielded fine crystalline particles of cubic SrTiO₃. Stepwise replacement of SrO₂ with BaO₂ in the reaction mixture generates a solid solution Sr _x Ba _y TiO₃ (x+y=1). Products were characterized by X-ray powder diffraction, scanning electron microscopy, energy-dispersive analysis of X-rays and Fourier transform-infrared spectroscopy. Thermal studies were monitored by thermogravimetric analysis and differential scanning calorimetry measurements.     

Electron microscopic studies of vacuum-evaporated (Pb1 −x Sn x )1 −y Te y thin films

Thin films of (Pb_{1 −x} Sn _x )_{1 −y} Te _y have been deposited by vacuum evaporation onto glass, mica, CaF₂ and NaCl substrates heated to various temperatures at low deposition rates. Transmission HEED, TEM and SEM studies have been carried out for as-grown films. HEED photographs show that (i) the degree of crystallinity of the films improves at higher substrate temperatures and (ii) the crystallites have smaller dimensions on CaF₂ than on NaCl, mica and even glass, under identical conditions of deposition. SEM studies reveal that with increasingT _sub, grains tend to form clusters through mobility coalescence. Needleshaped grains are formed when the deposition rate exceeds a certain critical value. Formation of needle-like grains has been attributed to the excess Te atoms possessing trigonal structure so that such grains can be observed only inp-type PbSnTe films.     

Thermally induced transformations in Ge x AsyTe100−x−y glasses

Chalcogenide glasses with compositions Ge_7.5As _y Te_92.5–y (y=20, 40, 45, 47.5, 50, 52.5, 55) and Ge₁₀As _y Te_90–y (y=15, 20, 22.5, 35, 40, 45, 50) have been prepared by the melt-quenching technique. The amorphous nature of these glasses has been confirmed by X-ray powder diffractometry. The thermal stability of these glasses has been studied using differential scanning calorimetry (DSC). The compositional dependence of the glass transition temperature,T _g, the crystallization temperatures,T _c1 andT _c2, and the melting temperature,T _m, are reported. The glass-forming tendency,K _gl, and the activation energy of crystallization,E, are calculated. The activation energy decreases with increasing tellurium content for both sets of glasses.