Temperature-dependent Raman scattering and x-ray diffraction study of phase transitions in layered multiferroic CuCrP2S6

Abstract

Functional van der Waals layered materials, which exhibit interesting phenomena such as magnetism and ferroelectricity, have been proposed for use in next-generation nanoscale devices and sensors. $\mathrm{CuCr}{\mathrm{P}}_{2}{\mathrm{S}}_{6}$ is a promising two-dimensional (2D) material that evinces multiferroic behavior where the $\mathrm{C}{\mathrm{u}}^{+}$ and $\mathrm{C}{\mathrm{r}}^{+3}$ cations are responsible for antiferroelectric and antiferromagnetic ordering, respectively. In this study, we use x-ray diffraction and Raman spectroscopy to map out these phase transitions in the range 70--400 K. The antiferroelectric phase transition is complex and shows a gradual transition to complete antipolar order with an intermediate quasiantipolar step. X-ray diffraction studies reveal evidence for negative thermal expansion across the antipolar phase transitions at \ensuremath{\sim}270 and \ensuremath{\sim}140 K. The latter of these is accompanied by a drastic reduction in rotational and translational mode frequencies of the anion groups in $\mathrm{CuCr}{\mathrm{P}}_{2}{\mathrm{S}}_{6}$. Our temperature-dependent structural data provide an important reference for subsequent research into this promising 2D multiferroic material.