The scientific activities of the laboratory of the physical acoustic

by usto

Scholars and engineers of the laboratory of physical acoustics conduct research in the following scientific areas:

1. Growing of Triglycine Sulfate Single Crystals (TGS) and an experimental study the phase transition in them by acoustic emission technique.

Brief relevant to conducted research information.

TGS single crystals of essential for AE tests sizes grown in the paraelectric phase by lowering the solution

AE analysis of the grown TGS crystals was carried out upon heating to temperatures above the Curie point (49°C) and subsequent cooling to room temperature. Kinks were detected in the curve of accumulation of the AE parameter RMS that indicates the sensitivity of this AE parameter to the dynamics of structural changes in the crystal.

AE comparative temperature tests carried out of samples of TGS crystals of nominal purity (industrial production) and of grown in the laboratory with growth defects. Spontaneous polarization in a defective TGS during a “disorder-order” phase transition gives rise to hundreds and thousands of AE events and continues for several days of monitoring. Defects put difficulties to the growth of domain walls, inhibit the formation of an ordered structure and delay the process of spontaneous polarization in time. In TGS crystal of nominal purity, due to the absence of defects, spontaneous polarization is completed within a few seconds, and just few AE events observed during the entire experiment.

AE studied in the process of forced domain switching in TGS under the constant electric field. AE dynamics was monitored during heating/ cooling of TGS in the presence of a field with a transition through T°K (Curie point), as well as at static temperatures: a) room temperature (22° C); b) close to T°K (45°C) and c) above T°K (60°C).

The influence of TGS extent of defectiveness: AE activity, i.e., the number of events per unit time, in the presence of an external electric field increases with the degree of defectiveness of the sample.

Influence of the field strength: it was found that AE accompanying the domain switching process. Exceeding the noise threshold of 22 dB recorded, starting from the applied field strength, above ~ 57-63V•cm. Under increased field strength, the amplitude spectrum of the AE expands due to the appearance of medium and maximal amplitudes. However, in a case the field vector is directed at an angle less than 90° to the polar axis, then, due to a decrease of the perpendicular component, the maximum amplitudes in the AE spectrum decrease from 60 to 40dB.The effect of temperature: with increasing temperature from room T° up to T°K, the mobility of domains increases, and the process of their switching is facilitated.  AE activity increases respectively.  In TGS crystal at 45°C in under applied perpendicular to the polarization axis field, the domain reconstruction that accompanied by a noticeable AE activity, begins when the field reaches 2kV. At the field strengthen to 2.4kV AE spectrum expands due to signals of large amplitudes of 45-50dB, which can be explained by the inclusion of larger domains to the switching process. If the polarity of the field, which voltage is higher than 2kV, reverses, the reverse of domains begins, noticeable in AE, but the AE activity decreases by half. When the field reaches 2.4 kV, the AE activity increases, but the widening of the AE amplitude spectrum does not reach the level of previous test. Supposedly, just domains, which did not manage to completely rebuild in the direction of the initially applied field, have been involved in the reverse switching process.