A Low-Temperature Specific Heat Study of the Giant Dielectric Constant Materials

TL;DR

This study investigates the low-temperature specific heat of giant dielectric materials, revealing low-lying excitations linked to lattice vibrations at grain boundaries, and proposes a model explaining their high dielectric constants.

Contribution

It provides new insights into the low-temperature excitations in giant dielectric materials and introduces a phenomenological model for their dielectric behavior.

Findings

Significant linear and Einstein contributions to specific heat at low temperatures.

Low-lying elementary excitations attributed to grain boundary lattice vibrations.

A proposed model explains high dielectric constants across frequencies.

Abstract

Low-temperature specific-heat study has been performed on the insulating giant dielectric constant material CaCu3Ti4O12 and two related compounds, Bi2/3Cu3Ti4O12 and La0.5Na0.5Cu3Ti4O12, from 0.6 to 10 K. From analyzing the specific heat data at very low-temperature range, 0.6 to 1.5 K, and moderately low-temperature range, 1.5 to 5 K, in addition to the expected Debye terms, we noticed significant contributions originated from the linear and Einstein terms, which we attributed as the manifestation of low-lying elementary excitations due to lattice vibrations occurred at the grain boundaries and induced by local defects. Together with the findings on electronic and mechanical properties, a phenomenological model is proposed to explain the high dielectric constant behaviors at both low and high frequency regions.