Thermoelectric Properties of TlIn1 – x Yb x Te2 (0.01 ≤ x ≤ 0.09) Crystals

The thermoelectric properties of TlIn_{1 – x} Yb _x Te₂ (0.01 x 0.09) crystals are studied. The results indicate that the crystals possess high thermoelectric figures of merit in the range 500–700 K.     

Preparation and Structure of Ga2 – x Sc x O3 (0.42 ≤ x ≤ 0.52)

The structure of a scandium gallium oxide single crystal grown by the Czochralski process from a charge of composition Ga_1.5Sc_0.5O₃ is determined by x-ray diffraction. The structure is shown to be a superstructure to -Ga₂O₃. The superstructure parameters are found to vary both along the axis of the crystal and radially, which is due to variations in Ga : Sc ratio. A structural model of the Ga_1.5Sc_0.5O₃ crystal is proposed.     

Diffusion of mercury into for HgxCd(1−x)Te 0≤x≤0.03

Experiments carried out to fabricate Hg_xCd_(1-x)Te by diffusing mercury into CdTe slices from the vapour, resulted in obtaining slices with a maximum value of x=0.004. Measurements on the diffusion of mercury into such slices, where 0≤x≤0.03, under saturated vapour pressure conditions, resulted in two component profiles, each profile giving two values of D. These results were similar to ones obtained earlier, indicating that the diffusion was rate-limiting. In addition, the diffusivities were found to be independent of x. This revised version was published online in July 2006 with corrections to the Cover Date.     

Phase Formation in the Course of Oxidation of In x Se1 − x Alloys (0.47 ≤ x ≤ 0.53)

We have determined the characteristic temperature ranges of heating of In _x Se_{1 – x} (0.50 x 0.52) alloys in air. We have established that the annealing of InSe powder in selenium vapors leads to the stabilization of the rhombohedral structure.     

Phase diagram of the CrxVSe2 system (0 ≤ x ≤ 1.0)

The phase diagram of the pseudo-binary CrVSe₂ (i.e. Cr_xVSe₂) system was determined by means of X-ray and DTA measurements, in the composition range 0≤x≤1.0. As the results, the following 6 phases have been confirmed to be existent in the temperature range 300≤T≤1100 : CdI₂,M₅X₈,M₃X₄,α,NiAs and Cr. Among them, M₅X₈,M₃X₄ and α phases undergo a phase transition to the CdI₂- or NiAs-type structures at high temperatures. The α phase (0.825≤x≤0.875 at 500°C) is a new phase firstly confirmed by this study.     

Preparation of the single phase γ′-(Fe1−x Ni x )4N compounds (0 ≤x ≤ 0.6)

Single phase -Fe₄N type (Fe_1–xNi_x)₄N compounds (0 x 0.6 have been synthesized for the first time by controlled heat treatment of iron-nickel oxalates in a gaseous flow of NH₃ xand H₂. The preparation processes were investigated using differential scanning calorimetry (DSC), X-ray diffraction and Mössbauer spectroscopy. The results confirmed that annealing of oxalates in the NH₃ and H₂ atmosphere included the processes of dehydration, decomposition and reduction, nitrogenation and thermal decomposition of the nitrides. The decomposition and reduction occur simultaneously. The final products depend on the flow rate ratio of NH₃ H₂ and the annealing temperature. The formation conditions for the single phase -Fe₄N type (Fe_1–xNi_x)₄N compounds are related to the nickel concentration, with increasing nickel content, the nitrogenation temperature decreased, in contrast the flow rate ratio of NH₃ H₂ increased.     

Photoconductivity in single crystals of (TlGaSe2)1−x(TlInS2)x alloys (0−0.45 ≤ x ≤0.55-1)

The spectral distribution of the photoconductivity in (TlGaSe₂)_1−x(TlInS₂)_x single crystals has been studied at 77 K and 300 K. At O ≤ x ≤ 4, Eg is observed to vary linearly with x. Eg(x) deviates from linearity at x = 0.6. This deviation is attributed to the effect of disorder in the composition. Over the range 0.6 to 2.2 eV pronounced impurity photoconductivity is detected at 77 K and 300 K. Deep impurity levels and their neighbourhood in this alloy are established to preserve their positions with the variation in the composition. The analysis of the obtained results indicates that the impurity centres are mainly connected with the cation neighbourhood.     

Appearance of Griffiths Phase in La0.7−x Pr x Ba0.3MnO3 (0 ≤x≤ 0.2)

Polycrystalline La_0.7?x Pr _x Ba_0.3MnO₃ (0 ≤x≤ 0.2) samples were prepared using solid-state reaction and checked by X-ray diffraction. Magnetization measurements versus temperature and applied magnetic field were used to investigate their magnetic properties. For samples with x= 0.2, the Griffiths phase is observed when the inverse of susceptibility (1/ χ vs. T) is analyzed.     

Conduction in nanostructured La1?x Sr x FeO3 (0 ≤ x ≤ 1)

We investigated electrical properties of nanostructured La_1?x Sr _x FeO₃ (0 ?? x ?? 1) from 300 K?C400 K. The nanostructured La_1?x Sr _x FeO₃ (0 ?? x ?? 1) was synthesized by citrate gel method requiring no pH control. X-ray diffraction pattern showed that single phase LaFeO₃ with an orthorhombic structure was formed. The structure changed into rhombohedral for x = 0.5 and it became cubic for x = 1.0. For x ?? 0.5, our material showed non-linear current-voltage characteristics and for x > 0.5 it showed linear current-voltage characteristics. Poole Frenkel type conduction mechanism was found to be operative in LaFeO₃ from 300 K?C400 K. The experimental values of field-lowering coefficient were by 2.56?C6.41 times higher than the predicted value and were attributed to the presence of localized fields. The increase in conductance with Sr content was due to formation of Fe⁴⁺ ions in addition to Fe³⁺ with the increase in Sr content. Impedance spectroscopy and ac conductivity analysis of La_1?x Sr _x FeO₃ (0 ?? x ?? 1) was also carried out in the temperature range from 300 K?C400 K and frequency was varied from 20 Hz - 2 MHz. The ac conduction followed the correlated barrier hopping model in La_0.9Sr_0.1FeO₃.     

Optical properties of amorphous (GeS)1 − x Bi x (0 ≤ x ≤ 0.15) films and a tentative cluster model for their structure

This paper examines the effect of Bi doping on the optical properties of amorphous (GeS)_{1 ? x} Bi _x (0 ≤ x ≤ 0.15) films. Experimental data in conjunction with first-principles electronic structure calculations for Ge _n S _m and Bi _n S _m clusters are used to derive a cluster model for the structure of the amorphous (GeS)_{1 ? x} Bi _x films.     

Ellipsometric study of dielectric functions of Mg(1-y)Ca(y)H(x) thin films (0.03≤y≤0.17)

Mg(1-y)Ca(y)H(x) (0.03≤y≤0.17) alloy thin films covered with thin Pd were hydrogenated using 4% H(2) in Ar under atmospheric pressure at room temperature. The complex dielectric functions (ε=ε(1) + iε(2)) in the range of 0.75 to 5.0 eV of these hydrides were evaluated with spectroscopic ellipsometry. The imaginary part of the dielectric function ε(2) was composed of one Drude and three Lorentz oscillator terms whose peak positions were about 1.2 eV (L(1)), 2.8 eV (L(2)), and 5.2 eV (L(3)). The L(3) term observed in all hydrides is attributed to optical absorption of MgH(2) with E(g)=5.16 eV. The Drude term, which may be due to unhydrogenated Mg-metal, was observed in the hydrides with a low Ca composition y of less than 0.04. The L(1) term was observed in the hydrides with a Ca composition of more than 0.05, while the L(2) term was observed for more than 0.11. These L(1) and L(2) terms were estimated from a variation with hydrogenation of ellipsometric angle Ψ which is due to optical absorption of CaH(2-α) (L(1)) and MgCaH(3.72) (L(2)).     

Crystal Structures and Magnetic Properties of the Co2Mn1−x V x Sb (0 ≤ x ≤ 1) Heusler Compounds

Crystal structure and magnetic properties of the Co₂Mn_1?x V _x Sb (0 ≤ x ≤ 1) Heusler compounds have been studied by X-ray powder diffraction (XRD), magnetometric measurements, and full-potential linearized augmented plane wave (FP–LAPW) method. All compounds crystallize in a cubic Cu₂MnAl-type crystal structure with the space group Fm–3m. The samples for x<0.8 have the Curie temperatures above room temperature, while the Curie temperature is observed at 68 K for the sample with x = 0.8. The saturation magnetization at 5 K decreases linearly with increasing vanadium concentration x. The values of the saturation magnetization obtained by FP–LAPW–local density approximation (LDA) calculations are in better agreement with the experimental results compared with the results obtained by FP–LAPW–generalized gradient approximation (GGA) calculations.     

Grain orientation and anisotropy in the physical properties of SrBi2(Nb1 − x V x )2O9 (0 ≤ x ≤ 0.3) ceramics

SrBi₂(Nb_{1 – x} V _x )₂O₉ (0 x 0.3 in molar ratio) ceramics have been fabricated via conventional sintering at elevated temperatures. Interestingly sintering the pellets in the 1320–1470 K temperature range yielded partially grain oriented ceramics. The orientation factor (f) monitored via X-ray powder diffraction studies was found to increase with increasing V₂O₅ content and reached 83% for x = 0.3. The increment in (f) was not that significant with increase in sintering temperature and its duration. The microstructural studies suggest that V₂O₅ has a truncating effect on the abnormal platy growth of SBN grains. The dielectric constant (_r) and loss (D) measurements as functions of both temperature and V₂O₅ content have been carried out along the directions parallel (_rp) and perpendicular (_rn) to the cold pressing axis of the pellet. The anisotropy (_rn/_rp) associated with _r was found to be 1.11 at 300 K and 2.1 at the Curie temperature, (T _c) respectively. Different dielectric mixture formulae that were employed to analyze the effective dielectric constants of these samples with varying porosity confirmed that the experimental value of _r was comparable with that obtained using Wiener's formula. Impedance spectroscopy was employed to rationalize the electrical behavior of these ceramics. The pyroelectric coefficients along the directions parallel and perpendicular to the pressing axis of the grain oriented (83%) SBN ceramic at 300 K were 0.13145 mC/m²K and 0.26291 mC/m²K respectively. The ferroelectric properties of these grain-oriented ceramics were better in the direction perpendicular to the pressing axis than those in the parallel direction.     

Magnetic Properties and Metamagnetic Transition in SmCo1−x Fe x AsO (0≤x≤0.2)

Polycrystalline SmCo_1?x Fe _x AsO (x=0, 0.05, 0.1, 0.2) materials with single phase have been synthesized by solid-state reaction. According to the X-ray diffraction patterns, the a-lattice parameter shrinks, but the c-lattice parameter expends with the increased amount of Fe doping. Complicated magnetisms consist of antiferromagnetic, ferromagnetic, and paramagnetic have been observed between 5 K and 300 K in the present system. Magnetic measurement shows that with increasing Fe content, antiferromagnetic order of SmCoAsO is suppressed and ferromagnetic order is enhanced. Below their antiferromagnetic transition temperature, metamagnetic transition can be detected in samples with x<0.2, and the transition field decreases with increasing Fe content. When Fe content reaches 0.2, no metamagnetic transition is observed down to 5 K. A canting of the spins plays a crucial role in metamagnetic behavior of the present system.     

Neutron investigation of Nd2-x-yCexLayCuO4 (0≤x≤0.2; y=0.5,1)

Samples of the electron-doped superconductor precursor Nd_2-x-yCe_xLa_yCuO₄ with 0x0.2 and y=0.5, I have been synthesized with a sol-gel method. While the as-prepared samples are in the normal state, oxygen reduction results in superconducting samples. The dependence of T_c upon Ce-doping x and oxygen content (4-) was determined in detail. It turned out that the internal pressure exerted by the La ions results in an extended superconducting range in x and compared to Nd_2-xCe_xCuO_4- Elastic neutron scattering was used to investigate the dependence of structural features upon doping. Upon oxygen reduction a non-isotropic shrinking of the unit cell (lattice parameter a increases, c decreases) and indications for interstitial oxygen were found. The local electronic surrounding of the Nd ions was observed via the crystal-field splitting by inelastic neutron scattering and turned out to be inhomogeneous. Such electronic inhomogeneities were previously measured for other high-T_c superconductors.     

Hydrothermal Synthesis and Transport Properties of FeS1-xTex (0 ≤ x ≤ 0.15) Single Crystals

Journal of Superconductivity and Novel Magnetism - In this work, a series of FeS1-xTex (0 ≤ x ≤ 0.15) single crystals were successfully synthesized by a hydrothermal method for the...     

Structure and Magnetostriction of (Dy_(0.7)Tb_(0.3))_(0.5)Pr_(0.5)Fe_x Alloys (1.10≤x≤1.85)

1. IntroductionInvestigation of rare earth-iron illtermetallic compounds is of great importance owing to their potential application as magnetostrictive transducerelemelltsll'ZI. It is possible to alloy the materials withthe same sign of magnetostriction but with the opposite sign of anisotropy in order to obtain the desiredratio of high magnetostriction to low magnetocrystalline anisotropy. The calculation of magnetostriction for rare earth-Fe Laves compounds indicates thatthe magnetostrict…     

The Structural and Magnetic Properties of Zn0.8−4x Dy x O y (0.05≤x≤0.10) Compounds Prepared by Solid-State Reactions

In this study, Dy-doped ZnO (Zn_0.8?4x Dy _x O _y (0.05≤x≤0.10)) samples were prepared by the solid-state reaction method, and were characterized by using the XRD, SEM and EDX techniques. The SEM results clearly demonstrate that the grains of the samples are very well connected to each other and tightly packed. From the XRD and EDX spectra, it has been concluded that the substituting of Dy³⁺ for Zn²⁺ in ZnO causes almost no change in the hexagonal wurtzite structure of ZnO. However, the lattice parameters a and c of Dy-doped ZnO are slightly different from those of the pure ZnO. These observations may be due to the slightly different ionic sizes of Zn²⁺ and Dy³⁺ ions. Our magnetization measurements (M–H) and (M–T) show paramagnetic behavior with a negative value of the Curie–Weiss temperature, corresponding to an antiferromagnetic exchange coupling in Dy-doped ZnO. Since, for low magnetic fields the extrapolation of the H/M versus temperature curves cut the T axes at negative values, we believe that the substitution of Dy in ZnO causes an overwhelming antiferromagnetic interaction for x≤0.10.     

Influence of the cation sublattice defectness on the electronic thermoelectric power of Li x Cu(2−x)−δ (x ≤ 0.25)

This paper presents an experimental study of the electronic thermoelectric power as a function of copper content for Li _x Cu_(2?x)?δS (x ≤ 0.25) electronic-ionic mixed conductors. Using a vacancy model for lattice defects, we calculate their electronic thermoelectric power as a function of x. By adjusting the hole effective mass, we reach satisfactory agreement with experimental data.     

Magnetocaloric Effects in Pr0.6−x Er x Sr0.4MnO3 (0.0≤x≤0.2) Manganese Oxides

The effects of partial substitution of praseodymium by erbium on the structural, magnetic, and magnetocaloric properties of Pr_0.6?x Er _x Sr_0.4MnO₃ (0.0≤x≤0.2) powder samples have been studied. Our polycrystalline compounds were synthesized by the conventional solid state reaction at high temperature. Rietveld refinement of the X-ray diffraction patterns using Fullprof program shows that all our samples are single phase and crystallize in the orthorhombic structure with the Pnma space group. The unit cell volume decreased with increasing the Er amount. Magnetic measurements show that all our samples exhibit a paramagnetic–ferromagnetic transition with decreasing temperature. The Curie temperature T _C shifts to lower values with increasing Er content. From the magnetization isotherms at different temperatures, magnetic entropy changes ΔS _M and relative cooling power RCP have been evaluated. The maximum of the magnetic entropy changes for the Pr_0.45Er_0.15Sr_0.4MnO₃ sample is found to be $| \Delta S_{M}^{\max } | = 2.66~\mathrm{J}\,\mathrm{kg}^{-1}\,\mathrm{K}^{-1}$ under a magnetic applied field change of 2 T.