1 research outputs found
New Antiferromagnetic Perovskite CaCo<sub>3</sub>V<sub>4</sub>O<sub>12</sub> Prepared at High-Pressure and High-Temperature Conditions
A new
perovskite, CaCo<sup>2+</sup><sub>3</sub>V<sup>4+</sup><sub>4</sub>O<sub>12</sub>, has been synthesized at high-pressure and high-temperature
(HP-HT) conditions. The properties of this perovskite were examined
by a range of techniques. CaCo<sub>3</sub>V<sub>4</sub>O<sub>12</sub> was found to adopt a double-perovskite cubic lattice [<i>a</i> = 7.3428(6) Ã…] with <i>Im</i>3Ì… 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 Co<sup>2+</sup> ions in CaCo<sub>3</sub>V<sub>4</sub>O<sub>12</sub> 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. CaCo<sub>3</sub>V<sub>4</sub>O<sub>12</sub> is a first example of perovskite in which the sites A′
are fully occupied by Co<sup>2+</sup> ions, and hence its synthesis
opens the door to a new class of double perovskites, ACo<sub>3</sub>B<sub>4</sub>O<sub>12</sub>, 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