Yield Behavior of Dislocation-Free Germanium from 500°C to the Vicinity of the Melting Point

The yield behavior of dislocation-free germanium has been measured over its entire plastic range. Crystals of germanium were stressed in tension from 500°C, where the crystals first deform without fracture, to 930°C (7°C below the melting point). Over this entire range a pronounced yield drop is observed. The shapes of the stress-strain curves at the highest and lowest test temperatures are remarkably similar even though the magnitudes differ by about a factor of 40. Both the maximum and flow stresses decrease exponentially with temperature and follow a relation of the form τ = A exp (E/kT). The maximum and flow stresses also were measured at constant temperature over two orders of magnitude change in strain rate. The results are compared with the theoretical predictions of the temperature and strain-rate dependence of the maximum and flow stresses.