Interfacial polarization-driven relaxation in CuO epitaxial thin films

Abstract

In this manuscript, we examine the electrical behavior of pulse laser deposition grown epitaxial (111) oriented CuO thin films using impedance spectroscopy to understand the microscopic origin of their relaxor-like characteristics. Temperature (T) dependent variation of the real part of dielectric permittivity (ε′) shows a relaxor ferroelectric-like anomaly with Vogel–Fulcher relation fitting well with the observed dielectric behavior, and thus, pointing toward a relaxor ferroelectric nature of the CuO thin film. However, the loss tangent and frequency-dependent dielectric spectroscopy measurements suggest the need to further explore the different mechanisms to understand the origin of observed relaxor behavior. Deconvolution of the impedance spectra reveals that interfacial contributions dominate in the dielectric response. Moreover, deconvoluted capacitances are temperature-independent within the specified temperature range, thereby excluding the possibility of a ferroelectric transition suggested by ε′ vs T data. The DC bias measurement of dielectric permittivity and I–V measurements reveal the MW (Maxwell–Wagner) nature of the observed dielectric anomaly. The measurements also suggest interface-limited Schottky conduction as the predominant conduction mechanism in the CuO thin films. This work demonstrates that the apparent relaxor behavior observed in the CuO thin film is related to extrinsic, i.e., interfacial polarization effect, instead of the intrinsic ferroelectric nature of the material.