Influence of charged walls and defects on DC resistivity and dielectric relaxation in Cu-Cl boracite

TL;DR

This study investigates how charged domain walls and defects influence the dielectric and resistive properties of Cu-Cl boracite, revealing the significant role of domain walls and point defects in its electrical behavior.

Contribution

The paper provides new insights into the impact of charged domain walls and point defects on the dielectric relaxation and resistivity of Cu-Cl boracite across phase transitions.

Findings

Charged domain walls exhibit altered conductivity and negative capacitance.

Dielectric relaxations are explained by point defects related to Cu valence changes.

Resistivity change at phase transition indicates domain wall contribution to conductivity.

Abstract

Charged domain walls form spontaneously in Cu-Cl boracite on cooling through the phase transition. These walls exhibit changed conductivity compared to the bulk and motion consistent with the existence of negative capacitance. Here, we present the dielectric permittivity and DC resistivity of bulk Cu-Cl boracite as a function of temperature (-140 {\deg}C to 150 {\deg}C) and frequency (1 mHz to 10 MHz). The thermal behaviour of the two observed dielectric relaxations and the DC resistivity is discussed. We propose that the relaxations can be explained by the existence of point defects, most likely local complexes created by a change of valence of Cu and accompanying oxygen vacancies. In addition, the sudden change in resistivity seen at the phase transition suggests that conductive domain walls contribute significantly to the conductivity in the ferroelectric phase.