On the Ferroelectricity in CaBaCo3.96Ni0.04O7

Abstract

Studies over the last decade demonstrate a large electric polarization and a substantial ferrimagnetic moment in CaBaCo4O7. The robust polarization, produced along the crystallographic c-direction, is however recently found to be a result of pyroelectricity rather than switchable polarization as in ferroelectricity. A contemporary investigation of lightly Nidoped CaBaCo4O7 derivatives claims switchable polarization indicating ferroelectricity in the materials. In an attempt to delve deeper into the debate, we have attempted direct P(E) loop measurements of two compounds as a comparison–a 1% Cr-doped (trivalent) and a 1% Ni-doped (divalent) CaBaCo4O7 derivative. The Ni-doped compound shows ferroelectriclike P(E) loops while the Cr-doped compound does not. We have also discussed the possible origin of the switchability of the polarization from the perspective of structural distortion and argued that a possible candidate is the buckling of the CoO4 tetrahedra rather than the cooperative orthorhombic distortion which only enhances the net pyroelectric polarization.