Bi 0.5 Pb 0.5 FeO 3 with Unusual Pb Charge Disproportionation: Indication of a Systematic Charge Distribution Change in Bi 0.5 Pb 0.5 M O 3 ( M : 3d Transition Metal) .

BiPbFeO with 1:1 mixture of Bi and Pb having charge degrees of freedom at the A-site of perovskite oxide ABO is obtained for the first time by high-pressure synthesis. Comprehensive synchrotron X-ray powder diffraction, optical second harmonic generation, Mössbauer spectroscopy, and hard X-ray photoemission spectroscopy measurements revealed that BiPbFeO is a canted antiferromagnetic insulator crystalizing in a nonpolar tetragonal 4/ structure with √2 × √2 × 2 unit cell and has unusually Pb charge disproportionated BiPbPbFeO charge distribution. The valence of transition metal in BiPbO changes from 3.5+ to 3+ and finally to 2+ from Mn to Fe and to Ni, from left to right in the periodic table as the 3d-level becomes deeper. The valences of Bi and Pb increase to compensate for the decrease in the 's valence, and Pb changes from 6s (2+) to 6s (4+) before Bi changes.