Atomic Simulations of Aurivillius oxides:: Bi3TiNbO9, Bi4Ti3O12, BaBi4Ti4O15 and Ba2Bi4Ti5O18 doped with Pb, Al, Ga, In, Ta

The Aurivillius oxides were originally of interest for their ferroelectric properties and have recently been explored in the field of oxide ion conductivity. Atomistic simulation methods have been carried out for Bi3TiNbO9, Bi4Ti3O12, BaBi4Ti4O15 and Ba2Bi4Ti5O18 doped with Pb, Al, Ga, In, Ta to determine defect energy in the materials by employing efficient energy minimization procedures. The calculations rest upon the specification of an interatomic potential model, which expresses the total energy of the system as a function of the nuclear coordinates. The Born model framework, which partitions the total energy into long-range Coulombic interactions and a short-range term to model the repulsions and van der Waals forces between electron charge clouds, is employed. This is embodied in the GULP Simulation code. Dopant solution energy versus ion size trends are found for both isovalent and aliovalent dopant incorporation at Bi and Ta sites. Trivalent dopants (Al, Ga, In) and Pb are more favorable on the Bi site, whereas Ta dopants preferentially occupy the Ti site.