E. Yu. Koroleva

Structure and dielectric response of Na1 − xKxNO2 nanocomposite solid solutions

This paper reports on the results of the investigation into the thermal evolution of the structure and dielectric properties of Na1 − xKxNO2 solid solutions (x = 0, 0.05, 0.10) embedded in porous glass with an average pore diameter of 70 ± 10 Å in the range 300–447 K, i.e., in the ferro-and paraelectric phases. The structural properties of the bulk and nanostructured materials are compared. It is shown that the introduction of small amounts of potassium brings about a noticeable change in the intensity ratio of the elastic Bragg peaks, while leaving the space group characterizing the structure of these nanocomposites unaffected. An increase in the potassium fraction does not result in a substantial decrease in the phase transition point. Measurements of the dielectric response have revealed that an increase in the potassium content gives rise to a marked “hardening” of the lattice in the premelting state, which reduces dielectric losses.

Longitudinal conductivity of thin films of La1 − xSrxF3 − x solid solutions on glass ceramics

The longitudinal conductivity of La1 − xSrxF3 − x solid solution films (x = 0–0.24) with thicknesses of 40–260 nm grown on glass ceramics at temperatures from room temperature to 300°C and frequencies of 10−1–106 Hz was studied by impedance spectroscopy. The concentration dependence of film conductivity on the SrF2 content had a maximum near x = 0.05. An equivalent circuit was constructed on the basis of the impedance plots to describe migration processes. The DC conductivity was evaluated for all samples under study. The activation energies were estimated from the temperature dependences of the DC conductivities of the films. The resulting dependences of electrophysical parameters were compared with those for bulk materials in terms of the relaxation conductivity model.

Behavior of the low-frequency conductivity of silver iodide nanocomposites in the superionic phase transition region

The behavior of the specific conductivity of composites based on silver iodide embedded in porous glasses with an average pore diameter of 7 ± 1 nm and in artificial opals with a pore diameter of 40–100 nm has been investigated in the temperature range from 300 to 500 K. It has been shown that a decrease in the characteristic pore size does not lead to a change in the order of the phase transition and that the temperature of the transition to the superionic state of silver iodide in a porous glass and in an opal upon heating is close to the phase transition temperature Tc in the bulk material (∼420 K). Upon cooling, the phase transition temperature Tc significantly decreases, and the phase transition becomes diffuse. With a decrease in the pore size, the region of the temperature hysteresis of the phase transition increases. The dc conductivities of the composites have been estimated from the impedance diagrams. The temperature dependence of the dc conductivity of both composites has a thermally activated nature, and the slope of the curve σ(1/T) changes near the phase transition, which indicates a change in the activation energy. The activation energies in the low-temperature and high-temperature phases have been estimated at ∼450–470 and ∼100 meV, respectively. The equivalent electrical circuit describing the charge transfer processes in the studied samples has been proposed.

The Schottky barrier at homogeneous impurity distribution in a semiconductor

The properties of the metal-semiconductor rectifying junction during the formation of a homogeneous diffuse distribution of electroactive defects in space-charge layers are discussed. The typical values of the effective Schottky barrier and its height fluctuations have been found in the absence of external field in the case of the low-temperature (∼500–700 K) redistribution of a shallow impurity. The Schottky barrier lowering in the junction and the typical inhomogeneity of the barrier height are of the order of the contact potential difference.

Production of Magnetic Alkali-Borosilicate Glasses by Induction Melting

The equipment and procedure for fabrication of magnetic alkali-borosilicate glasses by the method of induction melting are described. Field dependencies of the specific magnetization are presented and the values of the coercive fields (about 100 Gs) of the magnetic glasses are determined.

Degradation of GaAsP photocathodes under bombardment by ions of residual gases

Processes occurring in the near-surface region of semiconductor photocathodes based on an epitaxial multilayer GaAsP structure activated by a CsO monolayer have been investigated via secondary ion mass spectroscopy, X-ray luminescence spectroscopy, and electron microscopy. The main mechanisms of photoemitter degradation have been revealed. The main cause of degradation is low-energy heavy ion implantation into the near-surface region of the cathode, which changes the electron structure of the surface.

Investigation into the evolution of the structure of K1−xLixTa1−yNbyO3 single crystals under variations in temperature

The evolution of the structure of K1−xLixTa1−yNbyO3 single crystals with x = 0.001, y = 0.026, and 1900 ppm Cu (KLTN277) and with x = 0.0014 and y = 0.024 (KLTN123), which exhibit an extremely high permittivity (up to 4 × 105 in the quasi-static regime for the KLTN277 crystal), is investigated in the range from room temperature to 20 K. It is demonstrated that, upon cooling to the lowest temperatures, both crystals retain their cubic structure, but the lattice parameters pass through a minimum at the temperature of the observed anomalies of the dielectric response (∼50 K). In the neutron diffraction pattern of the KLTN123 sample, satellites appear in the vicinity of the (hhh) reflections at temperatures below ∼50 K. These satellites can be associated with the nucleation of the rhombohedral phase.

Structure and dielectric response of (1–x)NaNO2 + xBaTiO3 composites at x = 0.05 and 0.1

The (1–x)NaNO2 + xBaTiO3 composites of two compositions (x = 0.05 and 0.1) have been studied by powder neutron diffraction and broadband dielectric spectroscopy (frequency region 10–1–107 Hz). The temperature dependences of the ferroelectric order parameter of NaNO2 in the composites and pure NaNO2 have been measured. The frequency dependences of the real and imaginary parts of the permittivities of the composites and pure NaNO2 have been analyzed in the temperature range 25–187°C. The anomaly of the dielectric response observed at T ~ 147°C is assumed to be related to the processes of accumulation and “resolution” of charges at the BaTiO3 particle boundaries.