Dielectric anomaly in copper doped zinc sulphide

Unusually high values of dielectric constant of copper doped zinc sulphide powders have been obtained. They are discussed in terms of polarization catastrophe (PC) phenomenon. Because of the dependence both the hydrogen-like donor and effective mass approximation on the static dielectric constant of pure ZnS, the critical concentration of copper is lower for the hexagonal phase than for cubic one. This fact applied to the interpretation of our results, however, is heavily suppressed due to the unknown distribution of copper inside the crystallite. From the above reasons the strong dependence of the PC threshold on the real structure of the doped zinc sulphide is predicted.