Defect and dopant properties in CaMnO3

Navaratnarajah Kuganathan,Alexander Chroneos

doi:10.1063/5.0048401

Abstract

CaMnO3-based ceramics have been the subject of considerable research due to their potential application in solid oxide fuel cells, thermoelectric generators, and catalysis. The computational modeling technique based on the classical pair-wise potentials has allowed atomic-scale insights into the defect chemistry, diffusion of Ca2+ and O2− ions, and solution of various dopants in this material. The Ca/Mn anti-site was found to be the most favorable intrinsic defect suggesting disorder, which would be sensitive to synthesis conditions. The second most favorable disorder in CaMnO3 involves loss of CaO, resulting in calcium and oxygen vacancies, which in turn can promote vacancy mediated self-diffusion. The activation energy for oxygen migration (1.25 eV) is much lower than that for calcium (4.42 eV). Favorable isovalent dopants on the Ca and Mn sites were found to be Fe2+ and Ge4+, respectively. The formation of O vacancies can be facilitated by doping of single dopants Fe2+ and Al3+ on the Mn site. Dual dopants Ni–Fe and Al–Ga on the Mn site can also facilitate the introduction of oxygen vacancies required for the vacancy assisted oxygen diffusion.

Highlights

Perovskite-type oxides (ABO3) have become a material of increasing scientific interest in recent years as they exhibit a wide range of useful properties including thermoelectric, magnetic, and catalytic properties.[1,2,3,4,5] One of the key features of perovskites is that their structures are extremely flexible over metal-ion doping on either the A or the B site, maintaining their perovskite-type framework
The oxygen ion conductivities of these materials in both stoichiometric and non-stoichiometric forms have been studied well as the performance of advanced energy technologies such as solid oxide fuel cells is mainly dependent on the diffusion of oxygen ions.[10,11,12]
A significant effort has been made on the development of this material for use in thermoelectric power generators, electrocatalysis, and Li-ion batteries.[16,17,18,19,20,21,22]

Summary

Introduction

Perovskite-type oxides (ABO3) have become a material of increasing scientific interest in recent years as they exhibit a wide range of useful properties including thermoelectric, magnetic, and catalytic properties.[1,2,3,4,5] One of the key features of perovskites is that their structures are extremely flexible over metal-ion doping on either the A or the B site, maintaining their perovskite-type framework. The desired applications of these materials have been achieved by tailoring the A/B/O compositions mainly via substitutional doping.[6,7,8,9] The oxygen ion conductivities of these materials in both stoichiometric and non-stoichiometric forms have been studied well as the performance of advanced energy technologies such as solid oxide fuel cells is mainly dependent on the diffusion of oxygen ions.[10,11,12]. Perovskite-type CaMnO3 is one of the promising oxide materials that have found applications in several technologically relevant areas such as catalysis and power generation.[13,14,15] A significant effort has been made on the development of this material for use in thermoelectric power generators, electrocatalysis, and Li-ion batteries.[16,17,18,19,20,21,22] The thermoelectric properties of this material and its modified form have been previously investigated.[1,23–26]

Methods

Results

Conclusion