Infrared study of giant dielectric constant in Li and Ti doped NiO

TL;DR

This study investigates the infrared optical properties of Li and Ti doped NiO, revealing a composite structure with conductive grains and resistive boundaries that explains the giant dielectric constant via the Maxwell-Wagner mechanism.

Contribution

It introduces a three-phase granular model that accounts for the frequency and temperature dependence of the dielectric constant in doped NiO.

Findings

Observation of Drude-like absorption at low energy

Evidence of conductive grains and resistive boundaries

Extended Maxwell-Wagner model explains giant dielectric constant

Abstract

We have measured optical reflectivity of Li and Ti doped NiO (LTNO) in the infrared range at various temperatures. A Drude-like absorption is found at low energy, $\omega <$ 100 cm$^{-1}$ and its spectral weight increases substantially as temperature decreases. This observation and DC-resistivity result show that LTNO has a conductive grain and resistive boundary. Such composite structure provides evidence of the Maxwell-Wagner (MW) mechanism as the origin of the high dielectric constant $\epsilon_{o}$. We propose a three-phase granular structure and show that this extended MW model explains the observed frequency and temperature dependence of the dielectric constant as well as the giant value of $\epsilon_{o}$.