Charge-transfer electrostatic model of compositional order in perovskite alloys - art. no. 184113

We introduce an electrostatic model including charge transfer that is shown to account for the observed B-site ordering in Pb-based perovskite alloys. The model allows charge transfer between A sites and is a generalization o f Bellaiche and Vanderbilt's [Phys. Rev. Lett. 81, 1318 (1998)] purely elec trostatic model. The large covalency of Pb2+ compared to Ba2+ is modeled by an environment-dependent effective A-site charge. Monte Carlo simulations of this model successfully reproduce the long-range compositional order of both Pb- and Ba-based complex A(BB'B")O-3 perovskite alloys. The models are also extended to study systems with A and B-site doping, such as (Na1/2La1 /2) (Mg1/3Ta2/3)O-3, (Ba1-xLax)(Mg(1+x)/3Nb(2-x)/3)O-3, and (Pb1-xLax) x(Mg (1+x)/3Ta(2-x)/3)O-3. General trends are reproduced by purely electrostatic interactions, and charge transfer effects indicate that local structural r elaxations can tip the balance between different B-site orderings in Pb-bas ed materials.