Dielectric and polarization behavior of forsterite at elevated temperatures

The determination of the dielectric and polarization behavior of silicate minerals is important in the understanding of chemical bonding and the evaluation of interionic potentials in model calculations. The analysis of crystal-defect energetics and the atomistic theory of diffusion processes rely heavily upon the polarizability of component ions in the silicate. In this effort, dielectric constant (relative dielectric permittivity) and dielectric loss data have been obtained from capacitance measurements of single crystals of synthetic forsterite (Mg₂SiO₄) for orientations parallel to the a,b, and c crystallographic axes. Measurements were obtained as a function of temperature (25°C, 40-1000°C) and electric-field frequency (20 kHz-1 MHz). The static polarizabilities of forsterite at these temperatures are derived from the dielectric constants by utilizing the Clausius-Mosotti relation. The use of the polarizability additivity rule is confirmed for predicting the polarization of forsterite from the component oxides at high temperatures. Dielectric conductivities are determined from the dielectric loss values at 400-900°C and are in agreement with previous studies of single-crystal forsterite.