Screening Divalent Metals for A- and B-Site Dopants in LaFeO3

Abstract

Doping LaFeO3, a mixed ionic electronic conductor, can serve to increase its ionic and electronic conductivity, as observed in La1–xSrxCo1–yFeyO3−δ (LSCF), a promising intermediate temperature solid oxide fuel cell (IT-SOFC) cathode material. In this study, ab initio methods have been employed to assess the viability of a range of divalent A- and B-site dopants for promoting ionic and electronic conductivity, through calculating solution energies and binding energies to charge compensating species. For the A-site, we find that all alkali earth metals considered promote increased conductivity properties, but strontium and calcium have the lowest solution energies and therefore will be suitable dopants, in full agreement with experiment. Surprisingly, we find manganese, which has typically been assumed to dope exclusively on the B-site, to have significant probability, on the basis of energetic considerations, to occupy the A-site and be equally as energetically favorable as the traditional strontium dopant under certain conditions. For the B-site, cobalt and nickel were found to be suitable dopants, promoting ionic and electronic conductivity, due to the variable oxidation state of transition metals. Magnesium also increases conductivity as a B-site dopant in contrast with the other alkali earth dopants studied, which favor the A-site. By considering two compensation mechanisms, O2– vacancy and hole compensation, we show both oxygen vacancies and holes will be promoted in the doped system, in agreement with the experimentally observed mixed ionic electronic conducting properties of doped systems, including LSCF.