Dielectric properties of synthetic quartz crystals

Abstract

The dielectric constant (K) and loss (tanδ), and hence the conductivityσ), of high-quality synthetic quartz crystals have been measured with the electric field parallel (or perpendicular) to the optical axis (c-axis). These measurements are carried out in the frequency region 102 to 10⁷ Hz and in the temperature range 30 to 400° C. Values ofK at 30° C areE ‖c 4.58 andE ⊥c 4.36, and these are frequency independent; tanδ), values are quite low,E ‖c having larger values at 10² Hz compared toE ⊥c. The temperature variation ofK at different frequencies exhibits two regions: (i) a slow increase up to about 280° C which is frequency independent, and (ii) a fast increase beyond 280° C which is frequency dependent,K having larger values at lower frequencies; similar behaviour is exhibited by tanδ. Logδ), against 1/T plots show the usual extrinsic and intrinsic regions. The values for activation energy for conduction in the intrinsic region are calculated to be 0.85 and 1.0 eV, respectively, forE ‖c andE ⊥c. An attempt is made to understand these results.