Study on the electronics and structural properties of transition metal-doped La2Mo2O9.

Abstract

La2Mo2O9 is a potential electrolyte material for SOFC due to its higher oxygen conduction at high temperatures. However, La2Mo2O9 suffers from detrimental phase transition at high temperature from monoclinic α to cubic β phase. This phase transition can be prevented by lowering the temperature. However, lowering the temperature reduces the ionic conductivity. Substitution of transition metal on Mo site is the best strategy for the suppression of phase transition. In the present work, the effect of substituting element on different sites has been investigated. From the result, it is observed that the band gap increases with concentration of Er. For the assessment of mechanism behind the improved performance, the atomic insight is crucial. For that, we have employed ab initio DFT calculation. We have used PBE and grimme d3 dispersion correction for the accuracy of evaluated band gap and electrochemical stability. All DFT calculations have been performed using Quantum ESPRESSO pwscf code's and for the assessment of thermodynamical stability of La2Mo2O9 and the doped structures, an alternative descriptor, the global instability index (GII), which is based on the bond valance sum approach implemented in SoftBV was used. All the visualizations were done by XCrySDen and VESTA open source software.