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) .

Bi 0.5 Pb 0.5 FeO 3 with 1:1 mixture of Bi and Pb having charge degrees of freedom at the A-site of perovskite oxide ABO 3 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 Bi 0.5 Pb 0.5 FeO 3 is a canted antiferromagnetic insulator crystalizing in a nonpolar tetragonal I 4/ mcm structure with √2 a × √2 a × 2 a unit cell and has unusually Pb charge disproportionated Bi 3+ 0.5 Pb 2+ 0.25 Pb 4+ 0.25 Fe 3+ O 3 charge distribution. The valence of transition metal M in Bi 0.5 Pb 0.5 M O 3 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 M 's valence, and Pb changes from 6s 2 (2+) to 6s 0 (4+) before Bi changes.