A. P. Shpak

The nature and mechanism of charging of electron traps in Lu2SiO5:Ce3+ crystals

Investigation of the thermoluminescence (TL) properties depending on the temperature, UV irradiation dose, and activator ion concentration in Lu2SiO5:Ce3+ (LSO:Ce) crystals and measurements of the decay of recombination radiation during photostimulated release of the excitation energy accumulated in these crystals showed that a part of Ce3+ impurity ions exhibit ionization leading to the injection of electrons into the conduction band. The conduction band of a LSO:Ce crystal is involved in two opposite processes: the charging of electron traps and the recombination of electrons with Ce4+ ions. The transport of electrons to the traps has a diffusion character: electrons possess a significant mobility [D(315 K)=10−3 cm2/s] and can diffuse away from the donor ions to distances exceeding the lattice parameter of the crystal. The results of experiments with controlled atomic packing of LSO:Ce nanoclusters unambiguously demonstrated the key role of the structure of oxyorthosilicates in the formation of electron traps. The existing two-center model does not provide adequate description of the properties of electron traps and TL in LSO:Ce crystals.

The influence of crystalline anisotropy on the evolution of the crystallization front during directional solidification

The evolution of the crystallization front of transparent crystals of succinonitrile and pivalic acid in the course of directional solidification in the field of a temperature gradient (Bridgman method) is investigated experimentally. The influence of crystalline anisotropy is examined using single crystals of different orientations. Bulk (cylindrical) and planar single crystals of the materials under investigation are studied and compared for the first time. It is established that the crystallographic direction of growth plays an important role and determines the structure of the crystallization front at different stages of its evolution. New manifestations of the dynamic effects responsible for the development of the nonstationary periodic structure are revealed.

Diffuse-dynamic multiparameter diffractometry: A review

The results reported at the Conference on Application of X-Rays, Synchrotron Radiation, Neutrons, and Electrons in Nano-, Bio-, Information-, and Cognitive Technologies (RSNE-NBIC 2009) are briefly reviewed. This review is based on a cycle of studies [1–6] where a new method for studying the structure of real crystals—diffuse-dynamic multiparameter diffractometry (DDMD)—was proposed and substantiated.

Effect of a thermal factor on the concentration-structure ordering in ion-plasma W-Ti-B condensates

Small-angle X-ray scattering is used to study the effect of deposition and annealing conditions on the concentration-structure ordering in ion-plasma W-Ti-B condensates. At a relatively low condensation temperature of a solid solution (up to Tc = 770 K), the formed modulated structure has a uniform volume distribution of its structural elements. A stage-by-stage transition from a volume-modulated to a two-dimensional modulated structure is revealed when the condensation temperature increases from 570 to 1170 K. As the annealing time of the metastable postcondensation state of an ion-plasma condensate increases, the diffusion mobility of metallic atoms (W, Ti) decreases upon the formation of a modulated ordered structure. The action of a radiation factor in a three-electrode ion sputtering scheme enhances the concentration phase separation in a condensate, decreases the transition temperature, and stimulates an increase in concentration ordering wavelength λod.

In-situ observation of solid-liquid interface during directional solidification of succinonitrile and pivalic acid

The aim of this work is the direct study of the solid-liquid interface development in bulk 3D samples under directional solidification in different crystallographic orientations in ground and microgravity conditions. Flight experimental installation “MORPHOS” intended for directional solidification of transparent substances is under development. Ground-based experiments in 3D and quasi 2D samples are in progress.