Polar behavior of double perovskite (Bi,Pb)ZnNbO6 and (Bi,Sr)ZnNbO6: Density functional calculations
Abstract
The polar behavior of double perovskite (Bi,Pb)ZnNbO6 and (Bi,Sr)ZnNbO6 was investigated using first principles density functional calculations within the local density approximation. These materials have both A-site size disorder and ions with sterochemical activity. We found a strong ferroelectric distortion in both materials. The polarization of the Pb material is >80 μC/cm2 along the rhombohedral direction and the Sr based material is only slightly inferior. The high polarization results mainly from a large off-centering of Bi and the large Born effective charge of Nb, which yields a large contribution polarization although the Nb off-centers by a smaller amount. Neither of these materials favors a tetragonal state, and therefore solid solutions with PbTiO3 may show morphotoropic phase boundaries.