Temperature-induced A-B intersite charge transfer in an A-site-ordered LaCu3Fe4O12 perovskite
Temperature-induced A-B intersite charge transfer in an A-site-ordered LaCu3Fe4O12 perovskite
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DOI：
10.1038/nature07816
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发表时间：
2009-03-05
期刊：
影响因子：
64.8
通讯作者：
Shimakawa, Y.
中科院分区：
文献类型：
--
作者：
Long, Y. W.;Hayashi, N.;Shimakawa, Y.
过渡金属氧化物中价态的变化通常会导致其结构和物理性质的显著变化（1,2）。化学掺杂是调制这些价态的常规方法。在ABO(3)钙钛矿和/或类钙钛矿氧化物中，A位的化学掺杂可以在B位引入空穴或电子，从而产生特殊的物理性质，如高过渡温度超导性和巨大的磁阻（3,4）。当两个不同原子位置的价可变过渡金属同时参与时，我们期望能够诱导电荷转移，因此，通过使用小的外部刺激而不是引入掺杂元素来改变价。然而，显示这种类型的电荷转移的材料非常罕见，并且这种外部诱导的价态变化仅在高压等极端条件下才被观察到（5,6）。本文报道了A位有序双钙钛矿LaCu3Fe4O12在A位和B位异常温度诱导的价态变化；潜在的位间电荷转移伴随着材料结构、磁性和输运性质的显著变化。当冷却时，化合物在393 K时表现出一阶可逆转变，从B位含有Fe3.75+离子的LaCu32+Fe43.75+O12到a位含有稀有Cu3+离子的LaCu33+Fe43+O12。a位Cu和b位Fe离子之间的电荷转移导致顺磁性到反铁磁性和金属到绝缘体的等结构相变。与技术应用有关的更有趣的是，这种高于室温的转变与巨大的负热膨胀有关。
Changes of valence states in transition-metal oxides often cause significant changes in their structural and physical properties(1,2). Chemical doping is the conventional way of modulating these valence states. In ABO(3) perovskite and/or perovskite-like oxides, chemical doping at the A site can introduce holes or electrons at the B site, giving rise to exotic physical properties like high-transition-temperature superconductivity and colossal magneto-resistance(3,4). When valence-variable transition metals at two different atomic sites are involved simultaneously, we expect to be able to induce charge transfer-and, hence, valence changes by using a small external stimulus rather than by introducing a doping element. Materials showing this type of charge transfer are very rare, however, and such externally induced valence changes have been observed only under extreme conditions like high pressure(5,6). Here we report unusual temperature-induced valence changes at the A and B sites in the A-site-ordered double perovskite LaCu3Fe4O12; the underlying intersite charge transfer is accompanied by considerable changes in the material's structural, magnetic and transport properties. When cooled, the compound shows a first-order, reversible transition at 393 K from LaCu32+Fe43.75+O12 with Fe3.75+ ions at the B site to LaCu33+Fe43+O12 with rare Cu3+ ions at the A site. Intersite charge transfer between the A-site Cu and B-site Fe ions leads to paramagnetism-to-antiferromagnetism and metal-to-insulator isostructural phase transitions. What is more interesting in relation to technological applications is that this above-room-temperature transition is associated with a large negative thermal expansion.