Suppression of Intersite Charge Transfer in Charge-Disproportionated Perovskite YCu3Fe4O12

A novel iron perovskite YCu3Fe4O12 was synthesized under high pressure and high temperature of 15 GPa and 1273 K. Synchrotron X-ray and electron diffraction measurements have demonstrated that this compound crystallizes in the cubic AA′3B4O12-type perovskite structure (space group Im3̅, No. 204) with a lattice constant of a = 7.30764(10) Å at room temperature. YCu3Fe4O12 exhibits a charge disproportionation of 8Fe3.75+ → 3Fe5+ + 5Fe3+, a ferrimagnetic ordering, and a metal-semiconductor-like transition simultaneously at 250 K, unlike the known isoelectronic compound LaCu3Fe4O12 that currently shows an intersite charge transfer of 3Cu2+ + 4Fe3.75+ → 3Cu3+ + 4Fe3+, an antiferromagnetic ordering, and a metal–insulator transition at 393 K. This finding suggests that intersite charge transfer is not the only way of relieving the instability of the Fe3.75+ state in the A3+Cu2+3Fe3.75+4O12 perovskites. Crystal structure analysis reveals that bond strain, rather than the charge account of the A-site alone, which is enhanced by large A3+ ions, play an important role in determining which of intersite charge transfer or charge disproportionation is practical.