Synchrotron radiation diffraction in a single crystal of paratellurite investigated with a new experimental scheme.

First results are presented for synchrotron radiation diffraction in a paratellurite (TeO2) single crystal investigated with a new experimental scheme consisting of a standard monochromator and a relatively narrow slit for collimation and monochromatization of an incident beam. The Bragg case reflection geometry is used. The monochromator, a pair of Si crystals, maintains the initial direction of the beam propagation. The theory is developed for a precise description of the instrumental function in such a scheme. A new rocking curve registration technique with use of an adaptive bending piezoactuator is applied for the first time with the aim to record the narrow diffraction peaks with high accuracy. A sample is attached to one edge of the bidomain lithium niobate single crystal piezoactuator used. The piezoactuator is bent under the influence of an electric field and it changes the angular position of the sample with a very small step. The experimental curves are compared with the calculated diffraction rocking curves of a perfect paratellurite crystal, both the theoretical one and the one calculated taking into account the instrumental function. An instrumental function account allows a complete coincidence of the simulated curves with the experimental results to be obtained if the experimental curve does not coincide with the theoretical rocking curve. A small discrepancy between the theory and the experimental data has been discovered in cases where the incident beam is sufficiently collimated and monochromated. This indicates the presence of a certain number of lattice defects in the sample under study.

The Relationship of Precursor Cluster Concentration in a Saturated Crystallization Solution to Long-Range Order During the Transition to the Solid Phase.

A model for the transition from disordered liquid state to the solid phase has been proposed based on establishing a correlation between the concentration of precursor clusters in a saturated solution and the features of solid phase formation. The validity of the model has been verified experimentally by simultaneously studying the oligomeric structure of lysozyme protein solutions and the peculiarities of solid phase formation from these solutions. It was shown that no solid phase is formed in the absence of precursor clusters (octamers) in solution; perfect monocrystals are formed at a small concentration of octamers; mass crystallization is observed with an increasing degree of supersaturation (and concentration of octamers); further increase in octamer concentration leads to the formation of an amorphous phase.

Laboratory time-resolved X-ray diffractometry for investigation of reversible structural changes induced in single crystals by external electric field.

Time-resolved technique of X-ray diffraction curve measurement was implemented at a laboratory X-ray source using a high-speed data acquisition system. The time resolution of up to 100 µs was achieved via this X-ray diffractometry technique in the experiment of rocking curve dynamics measurement in a piezoelectric lanthanum-gallium silicate crystal under the influence of high voltage periodic pulsed electric field with an amplitude of 3.08 kV/mm corresponding to the pre-breakdown state. This perturbation caused a quick angular shift of the rocking curve caused by crystal lattice deformation due to the piezoelectric effect. The absence of the diffraction curve broadening effect was shown as well as the absence of the other significant relaxation-like variations of the curve parameters which are inherent for the migration of charge carriers (ions or vacancies) under the external electric field.