Formation of cross-sections for electron scattering by thermal lattice excitations in stainless steels

We present the results from experimental (in situ) measurements of the electrical resistance and thermal expansion of stainless steels in the temperature range 300–1000 K. Based on a correlation analysis of these properties, the decisive role of the thermal deformation of the atomic lattice in the formation of the electron scattering cross-section is established.     

Electroresistance and thermal expansion of electron solutions based on Cu and Zn

Experimental results of in situ measurements of the electroresistance and thermal deformation of electron solutions (Hume-Rothery phases) based on copper and zinc in the temperature region of 300 to 1000 K are presented. The connection between these properties, which is close to functional in each phase, is shown on the basis of correlation analysis.     

AC conductivity of BiFeO<Subscript>3</Subscript> ceramics obtained by spark plasma sintering of nanopowder

The structure and electrical properties of BiFeO₃ ceramics obtained by spark plasma sintering of a nanopowder are investigated. The nanopowder was synthesized by burning of an organic nitrate precursor. The ac conductivity was measured in a frequency range of 1 kHz–10 MHz in a temperature interval of 25–500°C. It is established that the temperature conductivity coefficients above and below ~350°C significantly differ with both alternating and direct currents. The frequency dependence of the conductivity obeys the Jonscher power law σ ~ ω ^s , where s < 1. The interpretation of this behavior is given in the framework of the model of correlated hops of charge carriers over potential barriers. It is assumed that the hopping mechanism is realized between Fe²⁺ and Fe³⁺ ions in ceramic grains. The role of oxygen vacancies in the conduction is also discussed.     

Magnetization and Static Magnetic Susceptibility of Fine-Crystalline High-Temperature YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> Superconductors Synthesized by the Sol–Gel Method

A comparative study of the magnetization and static magnetic susceptibility of high-temperature superconductors (HTSC) YBa₂Cu₃O_y synthesized by two variants of the sol–gel method with different average sizes of crystallites 〈 D〉 ranging 0.4–2 μm has been performed in constant magnetic fields (Н ≤ 6 kOe). It has been shown that the different annealing temperatures and times, at which their crystal structure is formed, change both the average sizes of crystallites 〈D〉 and the sizes of the structural homogeneity regions 〈l〉 and, at the same time, the magnetic field penetration depth (λ) and the coherence length (ξ). As a result, such parameters as 〈D〉 ~ λ and 〈l〉 ~ ξ become comparable, leading to a change in the physical characteristics of HTSCs. It has also been shown that the superconducting transition temperature T_c determined from the measurements of magnetic characteristics in constant magnetic fields remains within values optimal for superconductivity (T_c ≈ 92 K) in the case of an optimal number (y) of oxygen atoms, which determine the levels of charge doping for a given compound.     

Specific features of thermal resistance of silicon in the temperature range 105–130 K

Careful experimental investigations into the behavior of the thermal resistance of single-crystal silicon are carried out in the immediate vicinity of the temperature of an anharmonicity sign inversion (T _i =121.1 K), where phonon thermal resistance approaches zero. An anomalous positive deviation of the total thermal resistance (W) from the linear part of the temperature dependence with a maximum at 121.1 K is found in the temperature range 105–130 K. The temperature behavior of W in this range indicates that the mean free path of phonons is limited by a characteristic size of structural defects and that its temperature dependence exhibits specific features in the vicinity of T _i . It is established that the character of the temperature dependence of W above and below T _i is different. A linear functional relation between the total thermal resistance and the isobaric thermal strain is revealed at positive and negative anharmonicities of atomic vibrations.     

Structure and Dielectric Properties of Bi1 – xSmxFeO3 Nanostructured Ceramics

Physics of the Solid State - Structure and dielectric properties of polycrystalline multiferroics of Bi1&nbsp;–&nbsp;xSmxFeO3 (x = 0–0.2) system are studied. Using X-ray...     

Effect of heat treatment on the structure and properties of a BiFeO<Subscript>3</Subscript> nanopowder

This paper presents the results of an investigation of changes in the structure, magnetic, electrical, and thermal properties of a nanostructured bismuth ferrite powder prepared by the combustion of nitrateorganic precursors before and after heat treatment at temperatures of 500, 600, 700, and 800°C. It has been shown that there is a dependence of the magnetic properties on the dispersion of the particles. The specific features of the temperature and frequency dependences of the dielectric properties over wide ranges of frequencies and temperatures, as well as near the Néel temperature, have been considered.     

Linear dependence of the phonon thermal resistance of nonmetallic crystals on the isobaric thermal strain

This paper reports on the results of investigations into the thermal resistance W and thermal expansion coefficient β for single-crystal samples of Si, SiO₂, Al₂O₃, and NaCl. The available experimental data on the thermal resistance and thermal expansion coefficient for materials with different types of interatomic bonding and different Landau criteria for convection are analyzed. It is demonstrated that the reduced phonon thermal resistance is equal to the isobaric thermal strain at any temperature.     

Thermal expansion and kinetic coefficients of crystals

Electrical (ρ) and thermal (W) resistivities and thermal expansion coefficient (β) of Cu, Zn, Al, Pb, Ni, β-brass, Al₂O₃, NaCl, Si, SiO₂(∥), and SiO₂(⊥) were simultaneously measured with standard four-probe, absolute steady-state, and quartz dilatometer techniques. Measurements of Ni and β-brass were performed at temperatures from 300 to 1100 K and measurements of all other samples were made between 90 and 500 K. This temperature range includes the range below and above the Debye temperature (T_D). The total uncertainties of the specific electrical and thermal resistivities and thermal expansion coefficient (TEC) measurements are 0.5%, 3.0%, and (1.5-4.0%), respectively. The universal linear relationship between the electrical and thermal resistivities and βΤ over the wide temperature range was found experimentally. Using the Landau criterion for convection development for ideal phonon and electron gases in the solids, the universal relations, ρ^ph/ρ^*≡βT and W^ph/W^*≡βT (where ρ^ph is the phonon electrical resistivity, is the characteristic electrical resistivity, W^ph is the phonon thermal resistivity, and W^*=k_BG/qc_p is the characteristic thermal resistivity) between relative phonon electrical and phonon thermal resistivities and βΤ were derived. The derived universal relations provide a new method for estimating the kinetic coefficients (electrical and thermal resistivities) from TEC measurements.