(Invited) Potential Energy Landscape for Oxygen Vacancy Dynamics in Doped Ceria

Abstract

Ionic transport plays a key role in controlling a wide range of properties and processes important for applications such as catalysis, batteries, fuel cells, environmental sensors, and resistive random-access memory devices. For most of these applications, an outstanding need exists for ionically conducting materials with enhanced transport of charge carriers and consequently high conductivities at lower temperatures. The two most important factors that control the hopping transport of charge carriers are their concentration and mobility in the host structure. The effect of charge-carrier concentration on electrical conductivity has been investigated extensively over the last several decades in relation to transport in the bulk as well as near interfaces, and it is well-understood within the framework of microscopic and mesoscopic models of ionic conduction. In contrast, a fundamental understanding of the controlling factors for charge-carrier mobility in ionic conductors remains rudimentary at best, and it necessitates a detailed knowledge of the interactions between the mobile charge carriers and the potential energy landscape (PEL) provided by the immobile host lattice. In this contribution, we provide a comprehensive picture of the PEL for oxygen-vacancy migration in acceptor doped CeO2 based on the results from a combined application of nuclear magnetic resonance (NMR) and electrochemical impedance spectroscopy (EIS). We also present the results of our investigation on the effect of crystallite size on cation coordination environments and oxygen vacancy ordering in micro- and nanocrystalline doped ZrO2 and CeO2 by using high-resolution magic-angle-spinning NMR spectroscopy.