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

TL;DR

This study investigates the dielectric properties, relaxation processes, and conductivity mechanisms of hexagonal perovskites La1.2Sr2.7IrO7.33 and La1.2Sr2.7RuO7.33, revealing giant dielectric constants caused by electrode effects and intrinsic ionic hopping.

Contribution

It provides a comprehensive dielectric and infrared analysis of these perovskites, identifying intrinsic relaxation processes and confirming superlinear ac conductivity as a universal feature of disordered materials.

Findings

Giant dielectric constants up to 10^5 due to electrode polarization

Detection of two intrinsic ionic relaxation processes

Observation of superlinear power law in ac conductivity

Abstract

We present a thorough dielectric investigation of the hexagonal perovskites La1.2Sr2.7IrO7.33 and La1.2Sr2.7RuO7.33 in a broad frequency and temperature range, supplemented by additional infrared measurements. The occurrence of giant dielectric constants up to 10^5 is revealed to be due to electrode polarization. Aside of dc and ac conductivity contributions, we detect two intrinsic relaxation processes that can be ascribed to ionic hopping between different off-center positions. In both materials we find evidence for charge transport via hopping of localized charge carriers. In the infrared region, three phonon bands are detected, followed by several electronic excitations. In addition, these materials provide further examples for the occurrence of a superlinear power law in the broadband ac conductivity, which recently was proposed to be a universal feature of all disordered matter.