Solid Solubility in the Germanium Fluor-Phlogopite-Fluor Tetragermanic Mica System

Abstract

The solid solution in the germanium fluor-phlogopite (KMg₃AlGe₃, O₁₀F₂)-fluor-tetragermanic mica (KMg_2.5Ge₄, O₁₀F₂) system has been synthesized by the melting method and the resultant solid solution has been investigated by X-ray powder technique and infrared spectra. Furthermore, refractive index, density, and thermal expansion of the solid solution have been examined.
The results are summarized as follows: (1) With increasing amount of fluor-tetragermanic mica (T-G-M) in the solid solution, the cell dimension of the solid solution increases linearly. This result agrees with Vegard's rule. It indicates that all compositions between germanium fluor-phlogopite and fluor-tetragermanic mica form complete and continuous solid solution (KMg_2.5+0.5xAl_xG_4-xO₁₀F₂, 0×2). (2) The rates of change in spacings of planes among the end compositions are 0.23, 0.22, and O.38% in the directions of a, b, and c^* axes, respectively. In the direction of c^* axis it changes remarkably. (3) Most of absorption bands in the IR spectrum of the solid solution are assigned to Ge-O vibrations. With decreasing amount of fluor-tetragermanic mica (T-G-M) in the solid solution, the new band is clearly observed near 615 cm^-1 and it becomes gradually strong. This band is considered to be due to Al-O-Ge vibration. (4) With increasing amount of T-G-M in the solid solution, the refractive index and density of the solid solution increase linearly with molar composition. (5) With increasing amount of T-G-M in the solid solution, the thermal expansions in each axial direction of the solid solution increase continuously.