1 research outputs found
Structural and Magnetic Transitions in CaCo<sub>3</sub>V<sub>4</sub>O<sub>12</sub> Perovskite at Extreme Conditions
We investigated the structural, vibrational,
magnetic, and electronic
properties of the recently synthesized CaCo<sub>3</sub>V<sub>4</sub>O<sub>12</sub> double perovskite with the high-spin (HS) Co<sup>2+</sup> ions in a square-planar oxygen coordination at extreme conditions
of high pressures and low temperatures. The single-crystal X-ray diffraction
and Raman spectroscopy studies up to 60 GPa showed a conservation
of its cubic crystal structure but indicated a crossover near 30 GPa.
Above 30 GPa, we observed both an abnormally high “compressibility”
of the Co–O bonds in the square-planar oxygen coordination
and a huge anisotropic displacement of HS-Co<sup>2+</sup> ions in
the direction perpendicular to the oxygen planes. Although this effect
is reminiscent of a continuous HS → LS transformation of the
Co<sup>2+</sup> ions, it did not result in the anticipated shrinkage
of the cell volume because of a certain “stiffing” of
the bonds of the Ca and V cations. We verified that the oxidation
states of all the cations did not change across this crossover, and
hence, no charge-transfer effects were involved. Consequently, we
proposed that CaCo<sub>3</sub>V<sub>4</sub>O<sub>12</sub> could undergo
a phase transition at which the large HS-Co<sup>2+</sup> ions were
pushed out of the oxygen planes because of lattice compression. The
antiferromagnetic transition in CaCo<sub>3</sub>V<sub>4</sub>O<sub>12</sub> at 100 K was investigated by neutron powder diffraction
at ambient pressure. We established that the magnetic moments of the
Co<sup>2+</sup> ions were aligned along one of the cubic axes, and
the magnetic structure had a 2-fold periodicity along this axis, compared
to the crystallographic one