Specific Features of the Structure and the Dielectric Properties of Sodium–Bismuth Titanate-Based Ceramics

The phase formation, specific features, and the dielectric properties of the ceramics of compositions from the region of morphotropic interface in the (Na_0.5Bi_0.5)TiO₃–BaTiO₃ system modified by Bi(Mg_0.5Ti_0.5)O₃ and also low-melting additions KCl, NaCl–LiF, CuO, and MnO₂ that favor the control of the stoichiometry and the properties of the ceramics have been studied. The ceramics are characterized by ferroelectric phase transitions that are observed as jumps at temperatures near 400 K and maxima at T_m ~ 600 K in the temperature dependences of the dielectric permittivity. The phase transitions at ~400 K demonstrate the relaxor behavior indicating the existence of polar domains in the nonpolar matrix. An increase in the content of Bi(Mg_0.5Ti_0.5)O₃ favor a decrease in the electrical conductivity and dielectric losses of the samples, and the relative dielectric permittivity at room temperature ε_rt is retained quite high, achieving the highest values ε_rt = 1080–1350 in the ceramics modified with KCl.     

Dielectric Properties of Lithium–Titanium Ferrite Ceramics

The temperature dependences of the real and imaginary parts of the complex dielectric permittivities of ceramic Li–Ti ferrospinel are measured within the frequency range 10²–10⁶ Hz. The empirical expressions describing these dependences are derived and the frequency-independent electrophysical parameters of the material under study are obtained. The best agreement between the experimental and calculation data is achieved when the time constant and the static dielectric permittivity are decreasing functions of frequency. A model of relaxational processes accounting for this result is proposed. A certain role in polarization of the relaxation agents, whose reorientation is controlled by tunneling electron transitions inside the two-valence iron ion – three-valence metal ion, is assumed. It is stated that under certain conditions, the relaxation agent reorientation is likely to possess a collective character. The temperature dependences and are derived for a number of dc currents at different electric field strengths. Sharp variations in the dielectric characteristics of the ceramics are found.     

Preparation and Dielectric Properties of Nanostructured ZnO Whiskers

By a novel controlled combustion synthesis method, a large number of nanostructured ZnO whiskers with different morphologies, such as tetra-needles, long-leg tetra-needles and multi-needles, are prepared without any additive in open air at high temperature. The morphologies and crystalline structures of the as-prepared ZnO nanostructured whiskers are investigated by SEM and XRD. The possible growth mechanism on the nanostructured ZnO whiskers is proposed. The experimental results indicate that the dielectric constants and losses of the nanostructured ZnO whiskers are very low, demonstrating that the nanostructured ZnO whiskers are low-loss materials for microwave absorption in X-band. However, obvious microwave absorption in nanostructured ZnO whiskers is observed. The quasi-microantenna model may be attributed to the microwave absorption of the ZnO whiskers.     

Thermal Physical and Dielectric Properties of Bi1 – xErxFeO3

The heat capacity and the permittivity of multiferroics Bi_{1 – x}Er_xFeO₃ (x = 0, 0.10, and 0.15) have been studied in the temperature range 130–800 K. It is found that an insignificant substitution of erbium for bismuth significantly increases the heat capacity in a wide temperature range T > 300 K. The temperature dependence of the excess heat capacity is shown to be due to manifestation of the three-level states. An additional anomaly characteristic of a phase transition has been revealed in the temperature dependences of the heat capacity and the permittivity for the compositions with x = 0.15 at T = 587 K. The results of studies are discussed in combination of the data of structural studies.

     

Morphology and the Thermoelectric Properties of γ-GdxDy1 – xS1.5 – y Solid Solution Ceramics

Physics of the Solid State - The temperature dependences of the Seebeck coefficient, the electrical conductivity (T = 300–873 K) and also the heat conductivity coefficient, and the...     

Dielectric Properties of Fine-Grained BaTiO3 Ceramics under High Pressure

We investigate the temperature dependence of the dielectric constant of BaTiO3 ceramic with coarse to nanograin size under different hydrostatic high pressures up to 5000 bar in the range between room temperature and 200℃. The ferroelectric-to-paraelectric phase transition temperatures Tc are determined from the peak of dielectric constant versus temperature. The values of average grain-size are estimated from the SEM images. It is found that the magnitude of dTc/dp varies considerably from sample to sample depending on grain size. The Curie point Tc of the sample with small grain size decreases more sharply than that of samples with larger one.     

Structure and Magnetic Properties of (Ni1 – xZnx)Fe2O4 Ceramics with a Spatial Change in the Composition

Physics of the Solid State - Samples of homogeneous (x = 0, 0.1, and 0.2) and multilayer ceramics based on solid solutions of nickel–zinc ferrites (Ni1 – xZnx)Fe2O4...     

Synthesis and Luminescent Properties of Bismuth Titanates Bi1.6HoxTi2O7 – δ and Bi1.6Mg0.1HoxTi2O7 – δ

Physics of the Solid State - Pyrochlores Bi1.6HoxTi2O7 – δ and Bi1.6Mg0.1Ho xTi2O7 – δ, where x = 0, 0.01, 0.05, and 0.1, and...     

Dielectric and Pyroelectric Properties of （Pb0.50Sr0.50）TiO3 Ceramics

Lead strontium titanate （Pb0.50Sr0.50）TiO3 （PST） ceramics are prepared by the traditional ceramic processing. The dielectric constants and dielectric loss have been investigated in a temperature range from 25℃ to 300℃. The maximum dielectric constants for unpoled and poled samples are 9924 and 9683, respectively. The temperatures of phase transition for unpoled and poled samples are observed at 153℃ and 157℃, respectively. The phasetransition temperatures for unpoled and poled samples are not equal, which results from the polarization state of the domains. The remnant polarization and the coercive electric field are 18 uC/cm^2 and 6 kV/cm, respectively, from polarization-electric field （P - E） hysteresis loop. The temperature dependence of pyroelectric coefficients of the PST ceramics is measured by a dynamic technique. The dielectric constant and loss Lan δ of the poled PST ceramics are 813 and 0.010, respectively. The pyroelectric coefficients and figure of merit are 294 uC/cm^2 K and 13.6 × 10^-6 pa^-0.5, respectively, at room temperature 25℃and frequency lOOHz.     

A Study of the Structure and Magnetic Properties of FeRh1 – xIrx (x = 0.5–1) Alloys by First-Principles Methods

Physics of the Solid State - The structure and magnetic properties of FeRh1 – xIrx alloys (x = 0.5, 0.625, 0.75, 0.875, and 1) are investigated by first-principles methods...     

Thermal and Magnetocaloric Properties of La0.7Sr0.3 – xBaxMnO3 Manganites

Physics of the Solid State - The results of studying the effect produced by the partial substitution of Sr2+ ions by Ba2+ ions on the thermophysical and magnetocaloric properties of...     

Temperature Properties of Dielectric Permittivity and Optical Properties of a Multilayer Structure of Variozone Barium–Strontium Titanate

Physics of the Solid State - Optical properties and the temperature dependence of the permittivity of a multilayer structure of a variozone ferroelectric barium-strontium titanate deposited on a...     

Elastic Constants and Related Mechanical Properties of YxIn1 – xN Ternary System

Physics of the Solid State - Using a pseudo-potential approach within the virtual crystal approximation, the elastic properties of YxIn1 – xN semiconductor ternary alloys in...     

Dielectric and magnetic properties of Bi1−xYxFeO3 ceramics

Y doped BiFeO₃ polycrystalline ceramics were prepared by sol–gel method. Crystal structure examined by X-ray diffraction indicates that the samples were single-phase and crystallize in rhombohedral structure. An anomaly in the dielectric constant and dielectric loss in the vicinity of the antiferromagnetic Neel temperature (T_N) was observed. Saturated magnetization loops were observed for all sample with saturated magnetization M_s=0.678 emu/g and remnant magnetization M_r=0.084 emu/g for x=0.3.     

Dielectric functions and interband transitions of InxAl1 − xP alloys

We report pseudodielectric functions <ε> from 1.5 to 6.0 eV of In_xAl_1 − xP ternary alloy films. Data were obtained by spectroscopic ellipsometry on 1.2 μm thick films grown on (001) GaAs substrates by molecular beam epitaxy. Artifacts were minimized by real-time assessment of overlayer removal, leading to accurate representations of the bulk dielectric responses of these materials. Critical-point (CP) energies were obtained from numerically calculated second energy derivatives, and their Brillouin-zone origins identified by band-structure calculations using the linear augmented Slater-type orbital method.     

Anharmonicity of Lattice Vibrations and the Thermal Properties of Cd1 – xSrxF2 Solid Solutions

Physics of the Solid State - The temperature changes in the crystal lattice parameters a(T) of cadmium and strontium fluorides and also of their mutual Cd1&nbsp;–&nbsp;xSrxF2 (x =...     

Dielectric and Ferroelectric Properties of La-Doped SrBi2Nb2O9 Ceramics

Sr1-xLa2x/3Bi2Nb20O （0 ≤ x ≤0.2） ceramic samples are prepared by the solid-state reaction method. Their structure, dielectric and ferroelectric properties are investigated. The incorporation of La^3＋ improves the den- sification and decreases the grain size of the ceramics without changing the crystal structure. The remanent polarization 2PT increases with increasing La content and reaches a maximum value of 22.8μC/cm^2 at x = 0.125, which is approximately 60% larger than that of pure SrBi2Nb2O9. The Curie temperature keeps almost unchanged at a value of about 440℃. The relationship between doping and the ferroeleetrie and dielectric properties are discussed.     

The Influence of the Composition on the Atomic Structure of Bi1 – xYxFeO3 Ceramics

Technical Physics - The variation of the Bi1 – xYxFeO3 ceramics atomic structure with yttrium concentration x = 0, 0.10, 0.15, and 0.20 has been analyzed. Ceramic samples have been prepared...     

Detection of Surface States in Bi2 – xSbxTe3 – ySey Topological Insulators by Magnetotransport Measurements

Physics of the Solid State - In this paper, we studied the effect of the magnetic field and temperature on conductivity of Bi2&nbsp;‒&nbsp;xSbxTe3&nbsp;–&nbsp;ySey...