Structural phase transition in cobalt oxyfluoride Co3Sb4O6F6 observed by high-resolution synchrotron and neutron diffraction

Abstract

A structural transition was observed in non-centrosymmetric oxyfluoride Co3Sb4O6F6 at TS ∼180 K from a cubic phase (I4‾3m) to a c > a tetragonal phase (I4‾), through high-resolution neutron and synchrotron powder diffraction. In addition, specific heat, magnetization, and dielectric measurements were performed to investigate this phase transition. Although the specific heat and dielectric constant showed anomalies at TS, no transition to a ferroelectric phase was observed in the polarization hysteresis loop down to 30 K. Moreover, a magnetic structure analysis using neutron powder diffraction data revealed a transition from a paramagnetic phase to a G-type antiferromagnetic phase at TN ∼67 K, at which a peak was also observed in the specific heat measurements. The magnetic moments of Co2+ were aligned along the tetragonal c-axis with a Co2+ moment of 2.80(1) μB at 13 K. The rotation and deformation of the CoO2F4 octahedron due to the large displacement of F atoms were observed at TS from the structural analysis, which play an important role in the structural phase transition in Co3Sb4O6F6.