Isomorphous Substitution for Silicon in Fluorphlogopite

Attempts to substitute for silicon in the fluorphlogopite structure resulted in the synthesis of a fluorgermanium mica and a boron phosphate micalike orthorhombic crystal. The batch material contained Al2O3, MgO, MgF2, K2CO3, plus GeO2 for forming the fluorgermanium mica and BPO4 for forming the boron phosphate crystal. Optical analysis with a polarizing microscope and by X-ray diffraction verified the mica structure of the germanium crystal and disproved the mica structure of the boron phosphate crystal. The indices of refraction and unit-cell constants were determined for both crystals. A study of the electrical properties up to temperatures of 1000°F showed that the dielectric properties of the fluorgermanium mica were very similar to that of fluorphlogopite.