Exceptionally large room-temperature ferroelectric polarization in the PbNiO3 multiferroic nickelate: First-principles study

We present a study based on several advanced first-principles methods of the recently synthesized PbNiO3 [J. Am. Chem. Soc. 133, 16920 (2011)], a rhombohedral antiferromagnetic insulator, which crystallizes in the highly distorted R3c crystal structure. We find this compound electrically polarized with a very large electric polarization of similar to 100 mu C/cm(2), thus, even exceeding the polarization of well-known BiFeO3. PbNiO3 is a proper ferroelectric with polarization driven by large Pb-O polar displacements along the [111] direction. Contrary to naive expectations, a definite ionic charge of 4+ for the Pb ion cannot be assigned, and, in fact, the large Pb 6s-O 2p hybridization drives the ferroelectric distortion through a lone-pair mechanism similar to that of other Pb- and Bi-based multiferroics.