A COMPUTER-SIMULATION INVESTIGATION OF BROWNMILLERITE-STRUCTURED BA2IN2O5

Atomistic simulation techniques have been used to investigate the crys tal structure and defect energetics of Ba2In2O5. An interatomic potent ial model was developed that reproduces the orthorhombic brownmillerit e structure, with alternating layers of oxygen octahedra and tetrahedr a. Defect calculations show that the most energetically favorable intr insic defects are of the Frenkel type, with an oxygen vacancy on the O (1) site and an oxygen ion in an interstitial position in the tetrahed ral layer. Calculated formation energies of electronic defects suggest that Ba2In2O5 will oxidize with the formation of positive holes, cont ributing the electronic conductivity that is observed experimentally. Finally, consideration of possible oxygen ion migration pathways in th e structure found that energy barriers to migration are lowest between equatorial sites of oxygen octahedra in the [001] direction. (C) 1997 Academic Press.