Investigation of the Gliding Process in Ionic Crystals by Prismatic Punching

The prismatic punching method applies a unidirectional stress on a very small surface (approximately 0.001 square centimeter) of a crystal lying on a support which is softer than the crystal itself. The method is very convenient for low and high temperature and for small samples. The glide system of thallium bromoiodide crystals determined by the prismatic punching method contains dodecahedron planes (110) as glide planes and cubic planes [001] as glide directions. The width of the glide bands ranges from 1 to 5 microns. The stress-strain curve shows a linear relation between the shear angle $\delta$ and the applied stress $\sigma (\delta =a^{\prime }\sigma +b)$. The creep takes place according to the exponential law $\delta =a{t}^m$. The glide bands have to be displaced a distance of about 100 ions at room temperature and about 15 ions at -190°C before rupture takes place (plastic limit). Prismatic punching on sodium chloride crystals produces gliding along dodecahedron planes (110) in [1¯10] direction. Apparent cleavage of sodium chloride crystals along dodecahedron planes and normal cleavage along cubic planes are explained as ruptures between neighboring glide planes.