Apparent giant dielectric constants, dielectric relaxation, and ac-conductivity of hexagonal perovskites La1.2Sr2.7BO7.33 (B = Ru, Ir)

摘要

We present a thorough dielectric investigation of the hexagonal perovskitesLa1.2Sr2.7IrO7.33 and La1.2Sr2.7RuO7.33 in a broad frequency and temperaturerange, supplemented by additional infrared measurements. The occurrence ofgiant dielectric constants up to 10^5 is revealed to be due to electrodepolarization. Aside of dc and ac conductivity contributions, we detect twointrinsic relaxation processes that can be ascribed to ionic hopping betweendifferent off-center positions. In both materials we find evidence for chargetransport via hopping of localized charge carriers. In the infrared region,three phonon bands are detected, followed by several electronic excitations. Inaddition, these materials provide further examples for the occurrence of asuperlinear power law in the broadband ac conductivity, which recently wasproposed to be a universal feature of all disordered matter.