Suppression of Intersite Charge Transfer in Charge-Disproportionated Perovskite YCu3Fe4O12
Suppression of Intersite Charge Transfer in Charge-Disproportionated Perovskite YCu3Fe4O12
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DOI：
10.1021/ja312015j
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发表时间：
2013-04-24
影响因子：
15
通讯作者：
Takano, Mikio
中科院分区：
文献类型：
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作者：
Etani, Hidenobu;Yamada, Ikuya;Takano, Mikio
在15 Gpa、1273K的高压高温条件下合成了一种新型的铁钙钛矿YCu3Fe4O12。同步辐射X射线和电子衍射测试表明，该化合物在室温下为立方的AA‘3B4O12型钙钛矿结构(棒上空间群Im$3，第204号)，晶格常数a=7.30764(10)埃。YCu3Fe4O12在250K时同时表现出8Fe(3.75+)-gt；3Fe(5+)+5Fe(3+)的电荷歧化、亚铁磁性有序和类金属-半导体转变，不同于已知的等电子化合物LaCu3Fe4O12目前表现出3Cu2++4Fe(3.75+)-gt的位间电荷转移；3Cu(3+)+4Fe(3+)，反铁磁性有序，以及393K下的金属-绝缘体相变。这一发现表明，位间电荷转移并不是缓解A(3+)Cu3(3)(2+)Fe(4)(3.75+)O(12)钙钛矿中Fe3.75+态不稳定性的唯一途径。晶体结构分析表明，决定电荷转移或电荷歧化的是键应变，而不是被大的A(3+)离子增强的A位的电荷。
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 Im $$(3) over bar, No. 204) with a lattice constant of a = 7.30764(10) angstrom at room temperature. YCu3Fe4O12 exhibits a charge disproportionation of 8Fe(3.75+) -> 3Fe(5+) + 5Fe(3+), 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 3Cu(2+) + 4Fe(3.75+) -> 3Cu(3+) + 4Fe(3+), 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 A(3+)Cu(3)(2+)Fe(4)(3.75+)O(12) perovskites. Crystal structure analysis reveals that bond strain, rather than the charge account of the A-site alone, which is enhanced by large A(3+) ions, play an important role in determining which of intersite charge transfer or charge disproportionation is practical.