Abstract
We investigated the polar behavior of the double perovskite (Bi,Sr)2MgNbO6 using first-principles
density-functional theory calculations. We find that the magnitude (75 μC/cm2) and direction
(along [111]) of the polarization are comparable to our previous results for the A-site size difference
(Bi,Sr)2ZnNbO6 and (Bi,Pb)2ZnNbO6 systems. However, comparisons with the (Bi,Sr)2ZnNbO6
compound indicate that the presence of Zn modestly enhances the off-centering of the Sr and Nb
cations as well as the Born effective charges of both Bi and Nb. Analogous to the corresponding Pb-
based perovskites, Pb(Mg1/3Nb2/3)O3 and Pb(Zn1/3Nb2/3)O3, we demonstrate that the difference
in the experimentally observed critical temperatures are related to the differences in polarization
between the two materials. A local dipole analysis indicates that the most significant contribution
arises from the enhanced cooperative couplings with the larger Zn displacements.
