Elastic, piezoelectric, and dielectric properties of Ba(Zr0.2Ti0.8)O3-50(Ba0.7Ca0.3)TiO3 Pb-free ceramic at the morphotropic phase boundary Numerical approach to determine the elastic modulus of sintered natural hydroxyapatite J. Appl. Phys.

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The longitudinal and transverse modes of ultrasound propagation in Lead Zinc Niobate-Lead Titanate (PZN-PT) single crystal solid solutions are investigated as a function of temperature. The influence of an electric DC bias field on the elastic stiffness at various temperatures is studied. The presence of more stable phases induced by this electric field is observed. The polarization directions are modeled in terms of free energy function. The experiments are conducted in a dedicated temperature chamber working in a wide temperature range from 200 up to 470 K for ultrasonic measurements thin plate samples with the option for DC bias fields. The bias field was applied by a high voltage amplifier Trek model 610D. Crystal cuts of [001], [110] and [111] were used for the study of electric field poling conditions and temperature influence on structure induced by polarization orientation. A study of anomalies in sound velocity and relative attenuation near ferroelectric transitions is performed. It is well established that near the temperature of a second-order structural phase transitions, and in particular near the Curie point of ferroelectrics, anomalously strong ultrasonic absorption occurs.

It was shown that the dependence of the electric strength of solid dielectrics on the frequency is determined by the corresponding dependence of the dielectric constant and it decreases sharply in the region of dispersion frequencies in elastic oscillations and on relaxation oscillators (in the condition w 0 = 1/t) in relaxation oscillations.In the electrical form of breakdown, the electric strength is usually not a function of the temperature [1]. The thermal form of breakdown, where the electric strength is a function of the temperature, is observed at high temperatures. For ceramic dielectrics, we know that the region of electrical breakdown can extend to high temperatures, for example, up to 1000°C for aluminous ceramic (microlite), up to 600°C for GB-7 ceramic, and up to 120 -140°C for high-voltage electrotechnical porcelain. As our studies suggest, thermal breakdown in concretes begins in the 80 -90°C region (see Fig. 1). At lower temperatures (50°C), electrical breakdown is observed, where the deciding role is played by the local field acting on the charged particle in the dielectric.The dependence of the electric strength on the local field frequency in polarization processes was examined in [2]. Based on the model proposed by Lorentz, the local field strength E loc is the result of summation of the field strengths:where E 1 is the strength of the macroscopic field formed by polarized molecules outside of the Lorentz sphere, equal to P/(3e 0 ), where P is the polarization of the dielectric, equal to naE (n is the number of atoms with polarizability a; e 0 is the electric constant, equal to 8.85´10 -12 F/m); E 2 is the strength of the field created by dipoles located inside the sphere.The average macroscopic field is determined from the expression:where E 0 is the strength of the outer field applied to the dielectric.It is assumed that E 2 = 0 for structures of high symmetry and disordered structures. The strength of the local field is thus:Then the dipole moment of the unit of volume of a dielectric of complex composition will be described by the expression:where k is the number of varieties of polarizable particles. If we hypothesize that the local field strength at the dielectric point is a measure of the electric strength, the value of E s = E 0 is a quantity determined experimentally from Eqs. (1) and (2) and has the form:where e is the dielectric constant; w is the alternating current frequency. We see from Eq. (3) that the electric strength is proportional to the dielectric constant and decreases with an increase in the frequency. As a consequence, the dependence of the electric strength on the frequency for passive dielectrics such as glass, ceramic materials, and other inorganic dielectrics (concretes) can be analyzed with the frequency depen-

The possibility of modifying natural zeolites with bismuth salts and their effect on the electric properties are investigated. No phase transitions were found at the melting point of bismuth.Microporous framework aluminosilicates -zeolitesare technologically important minerals. Their characteristic physical and chemical properties (structural, ion-exchange, adsorption, electrical, and catalytic) are due to the porous structure of the aluminum-silicon-oxygen frames [1]. The presence of a system of channels, which are sufficiently wide for migration of extra-framework ions and molecules, as well as the very large surface area of the micropores make zeolites effective nano-exchangers, heterogeneous catalysts, and sorbents. The filled porous matrices are regarded as promising nanocomposite structures. It has been found that compounds based on porous materials with metals, polymers, liquids, and ferroelectrics influence melting and solidification phase transitions, atomic and molecular diffusion, and the superconductivity of this porous material. At pressures above critical values liquid metals penetrate into the channels of zeolites and form regular lattices, repeating the configuration of the channels and cavities of the framework. For this reason the development of the scientific principles of the preparation and industrial-scientific applications of zeolites is now an independent and important direction of research.The reserves of zeolite raw material in Russia are concentrated mainly in Trans-Baikal and the Far East. A significant part of these reserves is located in the Amur region (Vanginskoe and Kulikovskoe deposits) in the form of clinoptilolite and mordenite. They are highly effective in construction, including in the manufacture of concretes for different purposes. However, the zeoliticized rock from the Amur region has not been studied much and is essentially unknown outside the region.The aim of the present work is to investigate the modification of natural zeolites from the Amur region by bismuth salts Bi(NO 3 ) 3 and their effect on the electrical properties.The investigations were performed on pelleted samples made from natural zeolites (mordenite, clinoptilolite) from the Kulikovoskoe and Vanginskoe deposits in the Amur region. The samples were modified by bismuth salts Bi(NO 3 ) 3 prepared by dry pressing [2,3].The method of filling the natural zeolites with bismuth mineral salts consisted of the following [2, 3].1. A 1% salt solution was prepared from the bismuth salt Bi(NO 3 ) 3 . Several drops of HNO 3 were added in order to obtain valent bismuth atoms.2. Zeolite powder with 0.2 mm fraction was poured into the prepared solution in the proportion 5 parts zeolite + 20 parts solution.3. The prepared mixture was mixed for 1 day in a magnetic mixer.4. The mixture was filtered and dried first at room temperature and then in a drying furnace at temperature 150 -200°C for 5 h.5. The samples were prepared from the dry modified mixture by dry pressing.The electrical measurements were performed on samples in...