I. A. Osipenko

Dielectric, magnetoelectric, structure, and dissipative properties and the Mössbauer effect in PbFe1/2Nb1/2O3 ceramics in wide frequency and temperature ranges

High-quality fine-grained ceramic samples of classical multiferroics PbFe1/2Nb1/2O3 (PFN) were synthesized. Their dielectric, magnetoelectric, and magnetic characteristics, including the Mössbauer effect, were measured over wide ranges of temperatures (10–1000 K) and field frequencies (from 25 Hz to 1 MHz). The temperature dependence of the dielectric loss exhibits a maximum between 150 and 170 K, likely due to magnetic ordering. The dependence of ɛ on the magnetic field displays an anomalous increase near the Curie temperature (370 K) that rises to 40% upon heating.

The crystal and grain structure and physical properties of Bi1 − xAxFeO3 (A = La, Nd) solid solutions

High-quality ceramics were synthesized on the basis of Bi1 − xAxFeO3 (A = La, Nd; 0.00 ≤ x ≤ 0.20) solid solutions. Their crystal and grain structure, Mössbauer spectra, and other dielectric and magnetic characteristics were studied. It was shown that an increase in the content of A elements in the studied samples considerably enhanced their magnetic susceptibility and magnetoelectric effect.

Many-atom interactions in the theory of higher order elastic moduli: A general theory

The total potential energy of a crystal U({rik}) as a function of the vectors rik connecting centers of equilibrium positions of the ith and kth atoms is assumed to be represented as a sum of irreducible interaction energies in clusters containing pairs, triples, and quadruples of atoms located in sites of the crystal lattice A2: U({rik}) ≡ ΣN=14EN({rik}). The curly brackets denote the “entire set.” A complete set of invariants {Ij({rik})}N, which determine the energy of each individual cluster as a function of the vectors connecting centers of equilibrium positions of atoms in the cluster EN({rik}) ≡ EN({Ij({rik})}N), is obtained from symmetry considerations. The vectors rik are represented in the form of an expansion in the basis of the Bravais lattice. This makes it possible to represent the invariants {Ij({rik})}N in the form of polynomials of integers multiplied by τ2m. Here, τ2 is one-half of the edge of the unit cell in the A2 structure and m is a constant determined by the model of interaction energy in pairs, triples, and quadruples of atoms. The model interaction potential between atoms in the form of a sum of the Lennard-Jones interaction potential and similarly constructed interaction potentials of triples and quadruples of atoms is considered as an example. Within this model, analytical expressions for second-order and third-order elastic moduli of crystals with the A2 structure are obtained.

Theory of phase transitions under pressure in Si, Ge semiconductors

The bulk modulus of rigidity of Si and Ge phases stable under low and high pressures and the respective pressures of phase transitions under pressure are found in frames of Fermi model in the first approximation. The results of the calculations are compared with the results obtained in frames of quantum chemistry models.

Computing lattice sums for calculating the elastic moduli of bcc metals via cluster decomposition

The complete potential energy of a crystal

Two types of three-particle interactions and their influence on elastic constant temperature dependence

E\left( {\vec r_{ik} } \right)

Structure, dielectric, magnetoelectric, and dissipative properties of AFe2/3W1/3O3 (A = Ba, Sr, Pb) ceramics in wide frequency and temperature ranges

is presented in the form of an expansion in irreducible interactions in clusters containing pairs, triplets, and quadruplets of atoms, situated on A2 lattice sites. The full set of invariants