Zinc oxide single crystals: Influence of temperature and orientation of crystals on their mechanical properties

Abstract

Zinc oxide single crystals are grown hydrothermally and their microhardness is measured on different {hkil} faces in the temperature range from liquid nitrogen temperature to 900°C. The coefficient K 1C of fracture roughness and the surface energy γ of fracture are estimated. The (0001) plane of a positive monohedron is characterized by the maximum hardness and plasticity over the whole temperature range studied. The shape of indenter prints and dislocation rosettes on the planes of monohedra, hexagonal prisms, and the pyramid are studied. The indenter print on the basal plane has an isotropic shape, whereas on the planes of prisms and the pyramid the prints indicate the first-kind anisotropy of mechanical properties. The first-kind anisotropy coefficient k equal to H max/H min increases with an increase in the temperature for the \(\{ 10\bar 10\} , \{ 11\bar 20\} \), and \(\{ 10\bar 11\} \) planes. For the \(\{ 10\bar 10\} \) plane, the coefficient k varies from ∼1.4 at room temperature to ∼2 at 900°C.