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Abstract:
A new perovskite, CaCo32+V44+O12, 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) A] with Im (3) over bar 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 degrees 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 perovsldtes, ACo(3)B(4)o(12), 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.
