Influence of microstructure on resistance, photovoltaic response and piezoelectric voltage of Colemanite

Colemanite belongs to the class of prismatic monoclinic crystals. It is a hydrous compound and the water molecules contribute to conduction mechanisms at high temperature. The material contains interstitial and substitutional point defects which form intraband energy levels. These energy levels trap electrons and at high temperature the electrons gain enough energy to move to the conduction band. This phenomenon shows up as peaks in the current-voltage characteristics of colemanite. When excited with near ultraviolet light, colemanite exhibits ohmic resistance. The presence of photovoltaic microstructures such as grain boundaries, ferroelectric domains and others is responsible for this kind of behavior. The results show that colemanite may be used to generate higher photocurrent than conventional semiconductors. This opens up new possibilities of replacing semiconductors in photovoltaic device with colemanite. The piezoelectric response from different positions of colemanite varies in order of magnitude. These variations are due to the presence of point defects. The results may be used in the nondestructive testing of the uniformity of surfaces of piezoelectric crystals in general.