Evidence for power-law frequency dependence of intrinsic dielectric response in the CaCu$_{3}$Ti$_{4}$O$_{12}$

TL;DR

This study reveals that the dielectric response of CaCu$_3$Ti$_4$O$_{12}$ thin films is dominated by a power-law frequency dependence, supporting the extrinsic Maxwell-Wagner model for the colossal dielectric response observed in bulk CCTO.

Contribution

It demonstrates the power-law dielectric response in CCTO thin films and links oxygen content to changes in conductivity and dielectric behavior, providing insight into extrinsic effects.

Findings

Dielectric response is dominated by a power-law in frequency.

Oxygen annealing reduces film conductivity and alters dielectric response.

Below 80 K, dielectric response becomes frequency independent with ε'~100.

Abstract

We investigated the dielectric response of CaCu$_3$Ti$_4$O$_{12}$ (CCTO) thin films grown epitaxially on LaAlO$_3$ (001) substrates by Pulsed Laser Deposition (PLD). The dielectric response of the films was found to be strongly dominated by a power-law in frequency, typical of materials with localized hopping charge carriers, in contrast to the Debye-like response of the bulk material. The film conductivity decreases with annealing in oxygen, and it suggests that oxygen deficit is a cause of the relatively high film conductivity. With increase of the oxygen content, the room temperature frequency response of the CCTO thin films changes from the response indicating the presence of some relatively low conducting capacitive layers to purely power law, and then towards frequency independent response with a relative dielectric constant $\epsilon'\sim10^2$. The film conductance and dielectric response decrease upon decrease of the temperature with dielectric response being dominated by the power law frequency dependence. Below $\sim$80 K, the dielectric response of the films is frequency independent with $\epsilon'$ close to $10^2$. The results provide another piece of evidence for an extrinsic, Maxwell-Wagner type, origin of the colossal dielectric response of the bulk CCTO material, connected with electrical inhomogeneity of the bulk material.