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 ) 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(Zn 1/3Nb2/3)O3, we demonstrate that the differences 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.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 2011 Mar 21|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics