Deformation mechanism and photoplastic effects in CuBr single crystals

Abstract

Single crystals of CuBr with the zincblende structure, grown by the Bridgman method with KBr flux, have been deformed in compression between room and liquid-nitrogen temperatures. The resolved yield stress at room temperature is as low as 1.0 MN m⁻², but increases steeply below about 130K with decreasing temperature. The activation volume for plastic deformation decreases to less than 10 b³ (b is the magnitude of the Burgers vector) at shear stresses higher than 10 MNm⁻². These facts suggest that the Peierls mechanism controls the deformation at low temperatures.

Illumination with light during plastic deformation causes almost reversible hardening, the amount of which is undetectable at room temperature, increases with decreasing temperature and levels off below about 130 K. The effect is maximum for a wavelength slightly longer than the fundamental absorption edge. Below 130 K, illumination brings about another effect, namely irreversible softening, which is possibly caused by enhanced cracking.