INCLUSIONS OF THE HEXAGONAL PHASE IN CUBIC ZnS CERAMICS

IR Fourier reflectance spectra (50-500 cm(-1)) of ZnS ceramics synthesized by chemical vapor deposition (including those with additional hot isostatic pressing), hot pressing, and physical vapor deposition are presented. The samples are assumed to have a cubic crystallographic structure (sphalerite) because of the phase composition of the raw materials and the temperature prehistory of them. However, a weak band at similar to 295 cm(-1) that is characteristic of hexagonal ZnS crystals (wurtzite) manifests itself in both the reflectance spectra and the spectra of optical constants of all samples. Sphalerite -> wurtzite recrystallization below the nominal phase transition temperature (1023 degrees C) may be a consequence of the tendency ZnS to form the polytypical structure, which is facilitated in this ceramic material by the highly heterogeneous structure of the crystallites themselves.