A first principles analysis of the Colossal Ion Conductivity cubic Zirconia structural hypothesis and disorder, mechanics, and space charge mechanistic hypotheses

TL;DR

This paper uses first principles calculations to analyze the structural and mechanistic hypotheses of Colossal Ion Conductivity in cubic zirconia, concluding that CIC is likely an interface-mediated phenomenon rather than due to lattice melting, phase change, disorder, mechanics, or space charge effects.

Contribution

The study provides first principles evidence against existing hypotheses for CIC and proposes that CIC is an interface-mediated process, highlighting the need for further investigation.

Findings

No lattice melting or phase change observed under CIC conditions

Existing structural and mechanistic hypotheses fail to explain CIC

CIC likely involves interface-mediated mechanisms similar to grain boundary diffusion

Abstract

Colossal Ion Conductivity (CIC) is the phenomenon in which large changes in oxygen conductivity are observed when a solid state oxygen electrolyte is placed in a heterolayer super lattice. Several hypotheses have been posed concerning both structural changes of the ion conducting material and of the ion conducting mechanism. The posed structural hypotheses are oxygen sub lattice melting, phase change of the ion conducting material, and that the heterolayer environment does not induce a phase change of the ion conducting material. The posed mechanistic hypotheses are disorder, mechanics, and space charge. Here, first principles molecular dynamics and statics of the ion conducting interface are performed providing evidence that under CIC conditions no sub lattice melting nor phase change has occurred and that the electrolyte remains unchanged. A discussion of the posed mechanistic hypotheses is given and cast as a series of mathematical statements. When these hypotheses are compared with first principles calculations and literature results, they fail to capture CIC; a new alternative dipole hypothesis is offered, which also fails to capture CIC; further analysis of the literature points to CIC being an interface mediated phenomenon, similar to grain boundary diffusion, where the operando mechanism remain unclear.