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.     

Preparation and properties of Mn1.1Sb1 − y Al y and Mn1.1Sb1 − y Si y solid solutions

We have prepared Mn_1.1Sb_{1 ? y} Al _y (0 < y ≤ 0.2) and Mn_1.1Sb_{1 ? y} Si _y (0 < y ≤ 0.1) solid solutions with the B8 structure, in which the aluminum and silicon atoms substitute for antimony in the anion sublattice of manganese antimonide. Magnetic measurements have shown that substitutions within the stability region of the B8 phase have little effect on the mass magnetization and Curie temperature of the material. Mössbauer spectroscopy results confirm the anion nature of the substitutions.     

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.     

Crystal structure and magnetic properties of Sr1 − x Sm x Fe12 − x Co x O19 solid solutions

Sr_{1 ? x} Sm _x Fe_{12 ? x} Co _x O₁₉ (0 ≤ x ≤ 0.5) ferrites have been prepared by solid-state reactions in air at 1470 K using mixtures of samarium oxide, ferric oxide, Co₃O₄, and strontium carbonate. X-ray diffraction characterization showed that the samples with x < 0.2 were single-phase, whereas the samples with 0.2 ≤ x ≤ 0.5 contained α-Fe₂O₃ and those with 0.3 ≤ x ≤ 0.5 contained SmFeO₃, CoFe₂O₄, and Sm₂O₃ as well. The highest degree of Sm³⁺ and Co²⁺ substitutions for Sr²⁺ and Fe³⁺ (x) in the SrFe₁₂O₁₉ ferrite at 1470 K was determined to be slightly less than 0.2. This substitution only slightly decreases the a and c parameters of the hexagonal lattice and the Curie temperature (T _C) of the material. At temperatures of 5 and 300 K in magnetic fields of up to 14 T, we obtained magnetic hysteresis loops, which were used to evaluate the spontaneous magnetization (σ₀), specific saturation magnetization (σ_s), and coercive force (_σ H _c) of the ferrites. The experimentally determined 5-K spontaneous magnetization per formula unit (n ₀) of the x = 0.1 ferrite is 20.86μ_B, which coincides with the theoretical value calculated as n ₀ = (8 × 5) ? (3.9 × 5 ? 0.1 × 3) = 20.8μ_B. At 300 K, the n ₀ and _σ H _c of Sr_0.9Sm_0.1Fe_11.9Co_0.1O₁₉ exceed those of SrFe₁₂O₁₉ by 7.7 and 9.9%, respectively.     

Growth and properties of Ga y In1 − y P z As1 − x − z Bi x solid solutions on GaP substrates

Data are presented on temperature-gradient melt growth of GaInPAsBi solid solutions on GaP substrates. Heterophase equilibria in the Ga-In-P-As-Bi system are analyzed in terms of the regular solution model. The growth kinetics, composition, and structural perfection of GaInPAsBi/GaP heterostructures are investigated.     

Synthesis and properties of TlIn1 − x Gd x Se2 solid solutions

This paper describes the synthesis and crystal growth of TlIn_{1 − x} Gd _x Se₂ solid solutions and presents the T-x phase diagram of the TlInSe₂-TlGdSe₂ system. Partial gadolinium substitution for indium in TlInSe₂ increases the microhardness and unit-cell parameters of the material and reduces its band gap. According to X-ray diffraction data for TlInSe₂-TlGdSe₂ crystals, the TlIn_{1 − x} Gd _x Se₂ (0 < x ≤ 0.1) solid solutions crystallize in tetragonal symmetry and are isostructural with TlInSe₂.     

High temperature mechanical properties of La1−x Sr x Cr1−y Co y O3 for SOFC interconnect

Solid oxide fuel cells (SOFC) require an interconnect for fabrication into stacked cells. This is typically La(Sr, Ca)CrO₃, of which much data on the electrical and physical properties already exists. However, very little information exists on the high temperature mechanical properties of the material, which is a necessity for future design improvements. La_1–x Sr _x Cr_1–y Co _y O₃ samples were fabricated into green dry-pressed bars and pellets, and sintered under various heating and cooling regimes. The sinterability and high temperature mechanical properties of the material was then investigated as a function of the dopant concentration. It was observed, for example, that the modulus of rupture of the dry pressed La_0.7Sr_0.3Cr_1–yCo_yO₃ (y 0.3) gave a value of over 110 MPa at 1000 °C. This paper will provide data on the high temperature mechanical properties of the material and its application to the SOFC system.     

Microstructure and properties of Ba1 − x La x TiO3 ceramics with submicron grain size

Submicron grain size Ba_{1 ? x} La _x TiO₃ (x = 0.025–0.05) barium titanate ceramics have been prepared by two-step heat treatment. The grain size of the ceramics was 200–400 nm at x = 0.025 and 300–700 nm at x = 0.05, and the ceramics had increased dielectric permittivity (?_max ?23 000 at x = 0.025 and ?_max ? 46 000 at x = 0.05) compared to large-grained (>1 μm) materials.     

Dielectric properties of the system Ba1−xLaxTi1−xCo x O3

The dielectric behaviour of compositions withx=0.01, 0.05, 0.10 and 0.20 in the system Ba_1–x La _x Ti-_1-x Co _x O₃ was studied in the temperature range 300–473 K. The compositions withx = 0.01 and 0.05 show a diffuse ferroelectric-paraelectric phase transition, while other compositions do not show this transition in this temperature range. The frequency dependence of dielectric constant and dielectric loss in the samples withx0.05 indicates that spacecharge polarization contributes significantly to their observed dielectric parameters.     

The Effect of Zn-Substitution on the Anomalous Resistance Behavior of La1−x Ca x Mn1−y Zn y O3 Compounds

We have studied the effect of Zn substitution on the temperature dependence of the resistivity and the Curie temperature T _p of La_1–x Ca _x Mn_1–y Zn _y O₃ system (with x=0, y=0, and x=0.33, 0.00y0.15) during their pass to the paramagnetic conducting phase. All the specimens show a clear metal-insulator transition passing through the Curie temperature T _p . With increasing Zn concentration, T _p decreases for La/Ca substitution and also for Zn/Mn substitution with fixed 33 at.% of Ca. T _p is found to be slightly decreases for low concentrations of Zn (up to y=0.075) followed by a sharp decrease up to y=0.15. A possible explanation is given. Moreover, the activation energy E _a is calculated in the three different temperature regions characterized in the (-T) curve. Decreasing the temperature below T _p can increase the parallel alignment of the Mn spins and, thus decreases the resistivity of the samples. E _a increases with Zn content (up to y=0.075) followed by a sharp decrease. A strong correlation in the behavior of the normal state and residual resistivity as well as T _p and E _a with Zn content is reported.     

Dielectric properties of the Sr1−x La x Sn1−x Co x O3 system

The possibility of the formation of a solid solution in the Sr_1–x La _x Sn_1–x Co _x O₃ system has been explored. Single-phase solid solution forms in the compositions for x0.10. All single-phase solid solution compositions have a cubic structure similar to SrSnO₃. The dielectric behaviour of these solid solution compositions has been studied as a function of temperature and frequency. The frequency dependence of dielectric constant and dielectric loss in these materials indicates that space charge polarization contributes significantly to their observed dielectric parameters. Microstructural studies show the presence of well-faceted grains. The average grain size in these samples is small.     

Crystalline structure and dielectric properties of Ba(Ti1−y Ce y )O3

Crystalline structure, microstructure and dielectric properties for Ba(Ti_1–y Ce _y )O₃ (0 y 0.5) ceramics have been studied. Dense ceramics with the relative density higher than 95% and grain size of 0.7–1.5 m have been obtained. The limit of the solid solubility is determined as y = 0.3 by the X-ray diffraction, SEM, and dielectric properties measurements. The crystalline symmetry is tetragonal for the sample with y = 0.02 and cubic for y 0.06 at room temperature, and the unit cell increases with increasing Ce content in the solid solution range. Correspondingly, the dielectric response exhibits three dielectric peaks for y = 0.02, and one pinched dielectric peak with ferroelectric relaxor behavior for y 0.06.     

Magnetization Fluctuation Analysis and Superconducting Parameters of La1.5−x Ba1.5+x−y Ca y Cu3O z Superconductor

In this work we report analysis of experimental data of the magnetization of La_1.5?x Ba_1.5+x?y Ca _y Cu₃O _z superconducting system. The data are analyzed in terms of thermal fluctuations on the magnetization excess M(T) for different values of temperature in each of the samples. We describe a procedure for extracting the penetration depth in the ab plane (1537–1650 Å) and the coherence length in the ab plane (21–23 Å) parameters from the magnetization, as a function of the applied magnetic field. This procedure was performed for polycrystalline samples using the theory of Bulaevskii, Ledvij and Kogan, which analyzes the vortex fluctuation in superconducting materials within the Lawrence-Doniach framework. These data allowed one to determine the characteristic temperature value T ^? (53–73 K) in the magnetization curves for several magnetic fields. We calculated the data of magnetization excess from the curves of the magnetization as a function of the logarithm of the applied field. We notice that the values for these superconducting parameters are in agreement with reports for high-temperature superconductors. The value obtained of the superconducting volumetric fraction is compared with the value obtained through the measure of the Meissner effect.     

Synthesis and magnetic properties of polycrystalline films of Co x Fe y Cr3 − x − y O4 and Cr2O3/CoFe2O4 multiferroics

Magnetic properties of first obtained polycrystalline films of FeCr₂O₄, CoCr₂O₄, and CoFe_0.5Cr_1.5O₄ multiferroics and films of a Cr₂O₃/CoFe₂O₄ composite multiferroic have been studied. In particular, magnetization curves and temperature dependences of the magnetic moment of the samples were measured in the temperature range 4.2–300 K in fields of up to 10 kOe. It was shown that the Curie point of a multiferroic depends on its cation composition. It was found that an exchange bias of the hysteresis loop exists in films of the Cr₂O₃/CoFe₂O₄ composite multiferroic at temperatures below the Néel point of Cr₂O₃ (330 K).     

Transport Properties and Electronic Specific Heat of La2−x Ba x Cu1−y Zn y O4+d Bulk

The effect of the partial substitution of Cu by Zn and La by Ba in La: 214 prepared by conventional solid state reaction method has been investigated by using Hall coefficient, Seebeck coefficient and electronic specific heat measurements, over the wide temperature range between 4.2 K and 300 K, in magnetic fields up to 5 T. The samples with y=0 and d=0, showed superconductivity for x between 0.055 and 0.30. The critical temperature, the Hall and Seebeck coefficients strongly depend on Zn content. The phonon specific heat C _ph and electronic specific heat C _el have been extracted from the total specific heat C. Zn-doping effect on the (T)=C _el/T behavior suggests that the large range stripe order and the fluctuating stripe suppress the singlet formation and pseudo gap.     

Synthesis and magnetic properties of Ni x Fe1?x /Ni y Fe3?y O4 nanocomposite

Fe _x Ni_1−x /Ni _y Fe_3−y O₄ (0 < x, y < 1) nanocomposites were synthesized by the hydrothermal method in a rotating autoclave. The structure and magnetic properties of the composites have been investigated by Scanning electron microscopy (SEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The possible reaction mechanism was investigated in detail. These nanocomposites showed high special saturation magnetization Ms and relatively low coercive force Hc, which are 78.2 emu/g and 78.3 Oe, respectively.     

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.