The microstructure of piezoelectric lanthanum–gallium tantalite single crystals is shown to change substantially during cyclic mechanical actions at room temperature and during thermal shock: the dislocation density increases, twinning takes place, and a mesostructure forms. This effect is related to the appearance of piezoelectric fields, which significantly decrease the temperature of the onset of plastic deformation of these brittle single crystals, during mechanical actions.
When brittle lanthanum–gallium tantalite single crystals are subjected to cyclic loading and thermal shock at loads well below their yield strength, their microstructure changes substantially: the dislocation density increases by 3–4 orders of magnitude as compared to the initial state, twinning takes place, and a mesostructure forms. The crystals fail mainly via cracking along the x and y planes, which agrees with the anisotropy of microbrittleness of the crystals.
As follows from the calculation of the direct longitudinal piezoelectric effect, the electric field reaches 70 kV/cm on the opposite sides of x-cut LGT samples subjected to cyclic loading at a stress amplitude up to 20 kN/cm . This field results in a decrease in the cracking threshold in the crystals, restructuring of the dislocation structure in them, twinning, and a significant decrease in the temperature of the onset of plastic deformation in the brittle crystals.
The results of investigation of the mechanical properties of the crystals demonstrate that LGT crystals are promising materials under signalternating mechanical and thermal loading, where the level of signalternating loads reaches 20 kN/cm2 at a freuency of 100–150 Hz. The LGT crystals withstood thermal shocks upon quenching at a temperature difference of 120–150°C, and quenching at a larger temperature difference results in fracture of the crystals.
Ful text of this article is here!