DIELECTRIC PROPERTY OF OXYNITRIDE PEROVSKITES CONTAINING Ta{sup}(5+)

摘要

Dielectric properties of perovskite oxynitrides, ATaO{sub}2N (A = Ba, Sr, Ca), have been investigated by ac impedance spectroscopy using cold-isostatic-pressed polycrystalline powder specimens. Complex impedance spectroscopy is used to study dielectric properties of samples that cannot undergo an ordinary sintering process. Equivalent circuit analysis of impedance spectra showed that BaTaO{sub}2N and SrTaO{sub}2N are semiconducting (σ{sub}(el) ～ 10{sup}(-5) Ω{sup}(-1)cm{sup}(-1) and have unexpectedly high bulk dielectric constants, K ～ 4900 and 2900 respectively at room temperature. The dielectric constants of both compounds are frequency dependent and show a relatively weak, linear dependence upon temperature with no sign of a phase transition over the temperature range 300-180 K. However, CaTaO{sub}2N displayed distinctly different electrical behavior from the above two compounds: low dielectric constant (K< 20) and much lower electrical conductivity (σ{sub}(el) ～ 10{sup}(-8) Ω{sup}(-1)cm{sup}(-1)). The tantalum oxynitride perovskites have optical band gaps corresponding to visible range in contrast to classical white dielectrics.