Single crystal x-ray structure studies of multiferroic CuBr2 near its N\'eel transition

CuCl$_{2}$ was the first reported multiferroic in the halogen family\footnote{S. Seki et al.,\textbf{Phys. Rev. B} 82, 064424 (2010)}. CuBr$_{2}$ was later reported to be a multiferroic in the same family, but with a high transition temperature, T$_{N}$ = 73.5K\footnote{L. Zhao et al.,\textbf{Adv. Mat.} 24, 2469-2473 (2012)}. Although it has been reported to have spontaneous spin-driven ferroelectricity according to its polarization data, the reported temperature dependence of the dielectric constant lacks a sharp peak when crossing T$_{N}$, as is observed in CuCl$_{2}$. In order to probe the ionic displacements that are the origin of ferroelectricity in these materials, we performed hard X-ray diffraction studies of CuBr$_{2}$ as a function of temperature through T$_{N}$. Our data reveal no change in the lattice periodicity, however a change in the symmetry of the unit cell is clearly observed in the variation of the Bragg peak intensities with temperature. We will discuss the implications of these structure changes for the mechanism behind the magnetoelectric properties of CuBr$_{2}$.