Gyrotropic properties and birefringence of Smx Tb1−xFeO3 in spin reorientation range

The polar diagrams of the Sm_xTb_1−xFeO₃ system taken for the crystallographic directions [110] and [001] have been investigated. The gyrotropic measurements data are compared to the values of the bond angles θ₁ and θ₂ calculated in terms of the lattice parameters. The correlation between the crystallographic and optical properties change as a function of composition has been obtained for the system under investigation. -The temperature measurements of the gyrotropic properties of SmFeO₃ and Sm_0.8Tb_0.2FeO₃ have shown that with temperature rising a change of shape and character of the polar diagrams takes place. The birefringence temperature dependence for Sm_0.8Tb_0.2FeO₃ in the transparency and absorption range has been determined. The results of the study show the existence of the interrelation between the crystallographic, optical and magnetic characteristics and indicate that the temperature range of spin reorientation can be reliably determined from the optical measurements.     

Magnetic properties of the CrSxTe1−x (x = 0−0.2) solid solutions

On the basis of X-ray, magnetic and neutron diffraction measurements the range of solubility in the CrS_xTe_1−x (x = 0−0.2) system has been established and the magnetic phase diagram of the system has been plotted. The decrease of magnetization at low temperature and the additional reflections in the neutron diffraction patterns are associated with the formation of noncollinear magnetic structure which is characterized by the antiferromagnetic component of the magnetic moments. This component has the orthorhombic unit cell with \documentclass{article}\pagestyle{empty}\begin{document}$ a_M = \sqrt {3a_0 } $\end{document}, b_M = a₀, c_M = c₀. The character of the exchange interactions giving rise to this magnetic structure is discussed.     

Investigation of GaAs—InyGa1−yPzAs1−z–InxGa1−x-As grading heterojunctions formation

The initial stages of growth of GaAs–InGaAsP_var–In_xGa_1−xAs heterostructures (x = 0.1 and 0.17) were investigated for the equilibrium-cooling method of LPE growth. Similar investigations were carried out for GaAs–InGaAsP_var–In_0.05Ga_0.95As heterocompositions, but for the step-cooling technique. The scheme of growing of In_0.17Ga_0.83As films of GaAs substrates with several intermediate buffler InGaAsP_var layers is represented. These heterostructures were shown to have less than 10⁶ cm⁻² dislocation density on the overall area of the film (> 2 cm²).     

Electrochemical growth and properties of LaMn1−xCoxO3 (0 < x ≤ 1) single crystals

Single crystals of LaMn_1−xCo_xO₃ (0 < x < 1) with distorted perovskite structure have been obtained by the electrodeposition technique at anode from flux melt using Cs₂MoO₄‐MoO₃ binary system as solvent. An investigation of magnetic and electrical properties of the obtained crystals as well as its comparison with those for ceramic samples of the same composition were carried out. A much weaker interplay between magnetic and electrical properties and a smaller ∼8% magnetoresistance were found in the ternary oxide crystals slightly doped by Co on the verge of transition to ferromagnetic state in comparison to the data have been reported for LaMnO_3+δ single crystals. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Infrared optical properties of Cu1−xLixSe2 thin films

Infrared absorption spectra of Cu_1−xLi_xInSe₂ thin films are measured at room temperature in the wavenumber range from 100 to 600 cm⁻¹. The spectra exhibit two absorption bands in the wavenumber ranges 200–210 cm⁻¹ and 330–355 cm⁻¹ which are ascribed to vibrational modes due to In Se and Li Se vibrations, respectively. The influence of the phase transition from the chalcopyrite structure to the β-NaFeO₂ structure in the composition range x = 0.5–0.6 on the vibrational characteristics is established and discussed.     

Magnetically induced rhombohedral distortion in the UxTh1−xSe and UxY1−xSe solid solutions

Solid solutions of U_xTh_1−xSe for x = 1.00 ÷ 0.80 and the solid solutions of U_xY_1−xSe for x = 1.00 ÷ 0.60 were studied by the X-ray diffraction over the temperature range 100 ÷ 200 K. In both systems rhombohedral distortions of the cubic rock-salt crystal structure was observed below the Curie temperatures. The temperature and composition dependences of the rhombohedral angle ω of the rhomboedral cell and the \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{c' - a'}}{{a'}} $\end{document} ratio were determined.     

Controllable thermal expansion properties of In2 − xCrxMo3O12

Solid solutions In_{2 − x}Cr_xMo₃O₁₂ have been prepared via the solid state reaction method. The structural and thermal expansion properties have been characterized using X‐ray diffraction. All compounds exhibit monoclinic structure with space group P2₁/a at room temperature, and transform to orthorhombic structure at higher temperature. Compounds In_{2 − x}Cr_xMo₃O₁₂ (x = 0.7, 1.0 and 1.3) possess strong positive thermal expansion in the monoclinic structure, while their thermal expansion coefficients of orthorhombic structure vary from negative to positive with increasing Cr content. It is worthwhile to note that In_1.3Cr_0.7Mo₃O₁₂ and InCrMo₃O₁₂ have near zero thermal expansion properties.     

Polytypes of the system Fe1−xS

The structures of Fe_1−xS (0 < x < 0.135) are members of a family of derivative structures in the sense of Megaw. The NiAs structure as aristotype is the simplest and most symmetrical member of this family. The other polytypes of Fe_1−xS may be derived as hettotypes by lowering the symmetry. The loss of symmetry in changing from the aristotype to the hettotype may be of various kinds: small displacements of Fe and S atoms from the NiAs positions and/or Fe vacancies in some atomic planes occur. The structures of the system Fe_1−xS are interpreted as OD structures consisting of OD layers. The symmetry relations of the structures of FeS and Fe₇S₈ are described by OD groupoid families. Polymorphism, twinning and stacking faults are explained on this basis.     

Calculations of homogeneous region in Ga1−xAlxAs and GaAs1−xPx ternary solid solutions

Ternary solid solutions of A^IIIB^V compounds are considered as pseudobinary A(x)^IIIB(x)^v compounds, where the behaviour of A(x)^III and B(x)^v pseudoatoms is quite similar to A^III and B^v atoms in a binary A^IIIB^v crystal. Weak dependence of point defect contribution into Gibb's energy of A^IIIB^v crystal on its defect nature, random character of ternary solid solutions of A^IIIB^v compounds allow to use already for binary compounds developed formalism in the determination of component thermodynamic potentials of solid solution. Basing on literature data for the equilibrium solidus of AlAs the approximation for the temperature dependence of thermodynamic potential of an AB quasimolecule in A^IIIB^v crystal is revised. This result together with the well-known parameters for the equilibrium liquidus in Ga–P, Ga–As, and Al–As systems were used for calculations of the nonstoichiometric factor at the boundary of a homogeneous region in Ga_1−xAl_xAs and GaAs_1−xP_x ternary solid solutions. The results are compared with the known literature data.     

AlxGa1−xAs LPE growth

Al_xGa_1−xAs LPE growth was studied within the temperature range of 930–900°C with Al concentrations in solutions from 0.04 to 2.4 at.%. AlAs concentration in layers has been shown to grow with the cooling rate increase of solution. Interface and volume nucleation parameter dependence of K_i and K_v and formation time t_f on Al concentration in Ga solution have been found. Addition of Al to Ga solution increases critical values of As supersaturation (supercooling) and, as a result, increase in thickness of Al_xGa_1−xAs layers compared with GaAs layers have been determined in spite of As concentration lowering in Ga solution.     

SixGe1−xGaAs Heterojunction IMPATT-Diodes

Experimental research IMPATT-diodes on heterostructures Si_xGe_1−x-GaAs showed that the interphase boundary is noted with high thermal and radiation resistance. It is shown that such diodes are an equivalent alternative IMPATT-diodes with type of Schottky barrier.     

Concentration Magnetic Phase Transitions in the (La1−xCaxMnO3 System

Comprehensive investigations into crystal structures, electrical and magnetic properties of the (La_1−xCa_x)MnO₃ (x = 0 ÷ 0.6) solid solutions are performed. Two concentration magnetic phase transitions are found: antiferromagnetic-ferromagnetic with x = 0.14 and ferromagnetic (T_c = 150 K) - ferromagnetic (T_c = 260 K) at f = 0.2. It is shown that the first of them is due to the crystal structure O′ O orthorhombic transition, the second - to the increase of ferromagnetic interaction at the expense of additional interaction through conduction electrons. A diagram of the magnetic states for (La_1−xCa_x)MnO₃ at x = 0 / 0.6 is given.     

Heterophase states and a bridging phase in (1‐x)BiScO3 − xPbTiO3

Heterophase ferroelectric solid solutions of (1‐x)BiScO₃ − xPbTiO₃ are studied near the morphotrpic phase boundary (0.60 ≤ x ≤ 0.64). The role of non‐180° domain types of the P4mm and R3m phases in heterophase structures is studied in the context of the phase content. It is shown that the bridging Cm phase coexists with the adjacent phase (either P4mm or R3m), and different variants of an elastic matching ‘single‐domain Cm phase–polydomain P4mm phase’, ‘single‐domain Cm phase–polydomain R3m phase’ and ‘single‐domain Cm phase–near single‐domain R3m phase’ promote the complete stress relief. Based on these concepts and considering a minimum number of the domain types in the coexisting phases, we find a molar‐concentration dependence of the volume fraction of the Cm phase in the heterophase states. A correlation between the predicted volume fraction of the Cm phase and ratios of its unit‐cell parameters is first revealed. The role of the intermediate R3m phase in the phase sequence R3c − R3m − Pm$\overline 3$m and in the stress relief at x = 0.60 is discussed. Good agreement between the predicted and experimental data on the phase content is reached near the morphotrpic phase boundary.     

Quantitative analysis of Bi1−xSbx

The chemical composition of Bi_1-xSb_x alloys is determined by means of square-wave polarography, density measurements, measurements of the electron backscatter coefficient, and electron probe microanalysis. These experimental methods are discussed with respect to their results. At 10 keV, the electron probe microanalysis allows the determination of any antimony concentration without corrections (c_Sb = k_Sb).     

Liquidphasen-Epitaxie von Si-dotiertem AlxGa1−xAs

The liquidus and solidus isotherms of the quaternary phase diagram Ga—Al—As–Si have been estimated at 850 °C and N_Si = 0.04 and 0.1. Epitaxial layers were grown and the influence of silicon on the growth rate was investigated. Hall-effect measurements give informations on the dependence of the carrier concentration on the silicon content in the melt. The donor ionization energies vary from 32 to 69 meV and are diminished proportional to N.     

Synthesis and properties of α‐Fe2O3 nanorods

We report synthesis of α‐Fe₂O₃ (hematite) nanorods by reverse micelles method using cetyltrimethyl ammonium bromide (CTAB) as surfactant and calcined at 300 °C. The calcined α‐Fe₂O₃ nanorods were characterized by X‐ray diffraction (XRD), high‐resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). The result showed that the α‐Fe₂O₃ nanorods were hexagonal structure. The nanorods have diameter of 30‐50 nm and length of 120‐150 nm. The weak ferromagnetic behavior was observed with saturation magnetization = 0.6 emu/g, coercive force = 25 Oe and remanant magnetization = 0.03 emu/g. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Vickers indentation hardness of Hg1−xCdxTe

The Vickers indentation hardness of Hg_1−xCd_xTe has been measured as a function of composition x using monocrystalline samples of Bridgman and THM crystals and polycrystalline starting material at room temperature. The microhardness varied between 220 MPa (x=0) and 440 MPa (x=1), showing a maximum of 850 MPa at x ∼ 0.75, and was different between monocrystalline and polycrystalline samples. The “hardening rate” dH/dx is strongly dependent on the composition range and is discussed in context with solid solution hardening due to elastic interactions of solute atoms with gliding dislocations and ordering effects.     

Microhardness studies of K1−xRbxCl crystals

The microhardness measurements have been made on pure crystals of KCl, RbCl and mixed crystals of K_1−xRb_xCl. Microhardness varies non-linearly with composition being maximum near at the eqimolar composition. Microhardness values calculated from lattice parameter data are in good agreement with experimental data. The difference in the size of the ion constituting the mixed system is responsible for the internal strains giving rise to imperfections and inturn responsible for the non-linear variation of microhardness with composition.