Dielectric properties of LaPO₄ ceramics

Abstract

Dielectric constant (K) and loss (tanδ), and hence conductivity (σ), have been measured for LaPO₄ ceramics prepared by a molten urea process in the frequency region 10² to 10⁷ Hz and in the temperature range −193 to 280° C. At room temperature (≈ 30°C),K decreases with frequency up to 10⁵ Hz, beyond which it attains a constant value; tanδ behaves in a similar way. The values ofK and tanδ at 30°C and 10⁶ Hz for this material are 14 and 2.7 × 10⁻³, respectively. As a function of temperature,K exhibits two stages of increase: (i) a slow stage up to −30° C and (ii) a fast one beyond −30° C which is considerably frequency dependent,K having larger values at lower frequencies. Similar behaviour is exhibited by tanδ. Plots ofσ against 1/T for LaPO₄ exhibit the usual extrinsic and intrinsic regions; the activation energy for conduction in the intrinsic region is calculated to be 0.61 eV. It seems possible to understand the results through space charge polarization effects due to lattice defects in LaPO₄.