Charge-Order Melting in Charge-Disproportionated Perovskite CeCu₃Fe₄O₁₂

A novel quadruple perovskite oxide CeCu3Fe4O12 has been synthesized under high-pressure and high-temperature conditions of 15 GPa and 1473 K. 57Fe Mössbauer spectroscopy displays a charge disproportionation transition of 4Fe3.5+ → 3Fe3+ + Fe5+ below ∼270 K, whereas hard X-ray photoemission and soft X-ray absorption spectroscopy measurements confirm that the Ce and Cu valences are retained at approximately +4 and +2, respectively, over the entire temperature range measured. Electron and X-ray diffraction studies reveal that the body-centered cubic symmetry (space group Im3̅, No. 204) is retained at temperatures as low as 100 K, indicating the absence of any types of charge-ordering in the charge-disproportionated CeCu3Fe4O12 phase. The magnetic susceptibility and neutron powder diffraction data illustrate that the antiferromagnetic ordering of Fe ions is predominant in the charge-disproportionated CeCu3Fe4O12 phase. These findings suggest that CeCu3Fe4O12 undergoes a new type of electronic phase in the ACu3Fe4O12 series and that the melting of the charge-ordering in CeCu3Fe4O12 is caused by the substantial decrease in the Fe valence and the resulting large deviation from the ideal abundance ratio of Fe3+:Fe5+ = 1:1 for rock-salt-type charge-ordering.本研究在15 GPa、1473 K的高温高压条件下，合成了一种新型四元钙钛矿氧化物CeCu3Fe4O12。通过57Fe穆斯堡尔谱学（57Fe Mössbauer spectroscopy）表征发现，在约270 K以下会发生电荷歧化转变：4Fe3.5+ → 3Fe3+ + Fe5+。硬X射线光电子能谱与软X射线吸收光谱测量结果证实，在整个测试温度区间内，Ce与Cu的价态分别稳定维持在约+4与+2。电子衍射与X射线衍射研究表明，即便低至100 K的温度下，该材料仍保持体心立方对称性（空间群Im3̅，编号204），这说明发生电荷歧化的CeCu3Fe4O12物相中不存在任何形式的电荷有序。磁化率与中子粉末衍射数据显示，在该电荷歧化物相中，铁离子的反铁磁有序占据主导地位。上述研究结果表明，CeCu3Fe4O12在ACu3Fe4O12系列材料中展现出一种新型电子相；而该材料中电荷有序的熔解，源于铁价态的显著降低，以及由此导致的与岩盐型电荷有序所需的理想Fe3+:Fe5+ = 1:1丰度比出现较大偏差。