New Antiferromagnetic Perovskite CaCo₃V₄O₁₂ Prepared at High-Pressure and High-Temperature Conditions

A new perovskite, CaCo2+3V4+4O12, has been synthesized at high-pressure and high-temperature (HP-HT) conditions. The properties of this perovskite were examined by a range of techniques. CaCo3V4O12 was found to adopt a double-perovskite cubic lattice [a = 7.3428(6) Å] with Im3̅ symmetry. We have established that this new perovskite is stable at ambient conditions, and its oxidation and/or decomposition at ambient pressure begins above 500 °C. It undergoes an abrupt antiferromagnetic transition around 98 K. Electrical resistivity data suggest semimetallic conductivity in the temperature range of 1.6–370 K. We have established that the Co2+ ions in CaCo3V4O12 are in the high-spin state with a sizable orbital moment, even though their square-planar oxygen coordination could be more suitable for the low-spin state, which is prone to Jahn–Teller distortion. Electrical resistivity curves also exhibit a distinct steplike feature around 100 K. CaCo3V4O12 is a first example of perovskite in which the sites A′ are fully occupied by Co2+ ions, and hence its synthesis opens the door to a new class of double perovskites, ACo3B4O12, that may be derived by chemical substitution of the A sublattice by lanthanides, sodium, strontium, and bismuth and by other elements and/or of the B sublattice by some other transition metals.本研究在高温高压（HP-HT）条件下合成了一种新型钙钛矿(perovskite)材料CaCo²⁺₃V⁴⁺₄O₁₂。研究团队采用多种实验表征手段对该钙钛矿的性能开展了系统测试。结果表明，CaCo₃V₄O₁₂具有双钙钛矿型立方晶格结构，晶格常数a=7.3428(6) Å，空间群为Im3̅。本研究证实该新型钙钛矿在常温常压条件下可稳定存在，在常压环境中其氧化或分解反应的起始温度高于500 ℃。该材料在约98 K处发生突变型反铁磁相变。电阻率测试数据显示，在1.6~370 K的温度区间内，该材料表现出半金属导电特性。本研究进一步明确，CaCo₃V₄O₁₂中的Co²+离子虽处于平面正方形氧配位环境（该环境更易形成易发生姜-泰勒（Jahn-Teller）畸变的低自旋态），但实际呈现高自旋状态，并伴随可观的轨道磁矩。电阻率曲线在约100 K处呈现出显著的阶梯状特征。CaCo₃V₄O₁₂是首个A'位点完全被Co²+离子占据的钙钛矿材料，其合成工作为新型双钙钛矿家族ACo₃B₄O₁₂的研发开辟了可行路径：该类材料可通过对A亚晶格进行镧系元素、钠、锶、铋等元素的化学取代，或对B亚晶格进行其他过渡金属元素的掺杂改性得到。