Dielectric Loss due to Impurity Cation Migration in α Quartz

Abstract

The dielectric constant and loss factor of natural quartz single crystals have been measured in the temperature range from room temperature to 573°C, and in the frequency range from 50 cps to 100 kc/sec. Parallel to the c axis a large dispersion in the dielectric constant of the order of ε_s‐ε_∞ = 500 was observed. Associated with this dispersion is a peak in the loss factor of the order of ε″_max = 250. The data were analyzed in terms of the Debye equations with a single thermally activated relaxation time. The activation energy is about 16.7 kcal/mole. Perpendicular to the c axis no peak in ε″ was observed, but both ε′ and ε″ begin to increase at low frequencies and high temperatures. The loss peak parallel to the c axis was substantially reduced when impurities were removed by electrolysis. The introduction of Ag, Cu, or Na gave rise to new peaks while Li tended to reproduce the original peak. It is concluded that the original loss was due to the motion of Li⁺ ions along structural channels parallel to the c axis. From the charge transported in electrolysis experiments, it can be inferred that the number of ions involved was about 5×10¹⁷ per cm³. The observed activation energy is believed to be the Coulomb binding energy between a substitutional Al³⁺ ion and an interstitial Li⁺ ion.