Real Space Imaging of the Microscopic Origins of the Ultrahigh Dielectric Constant in Polycrystalline CaCu3Ti4O12

TL;DR

This study combines multiple microscopy and spectroscopy techniques to reveal that the ultrahigh dielectric constant in polycrystalline CaCu3Ti4O12 originates primarily from grain boundary effects, especially their resistive and capacitive properties.

Contribution

It provides direct microscopic evidence linking grain boundary behavior to the ultrahigh dielectric constant in CCTO, clarifying its microscopic origin.

Findings

Grain boundaries dominate the dielectric response.

Potential drops are localized at grain boundaries.

Strong capacitive coupling occurs at interfaces.

Abstract

The origins of an ultrahigh dielectric constant in polycrystalline CaCu3Ti4O12 (CCTO) was studied using the combination of impedance spectroscopy, electron microscopy, and scanning probe microscopy (SPM). Impedance spectra indicate that the transport properties in the 0.1 Hz .. 1 MHz frequency range are dominated by a single parallel resistive-capacitive (RC) element with a characteristic relaxation frequency of 16 Hz. Dc potential distributions measurements by SPM illustrate that significant potential drops occur at the grain boundaries, which thus can be unambiguously identified as the dominant RC element. High frequency ac amplitude and phase distributions illustrate very weak contrast at the interfaces, which is indicative of strong capacitive coupling. These results demonstrate that the ultrahigh dielectric constant reported for polycrystalline CCTO materials are related to the grain boundary behavior.