Low Temperature Symmetry of Pyrochlore Oxide Cd2Re2O7

Abstract
We report the X-ray study for the pyrochlore oxide Cd 2 Re 2 O 7 . Two symmetry-lowering structural transitions were observed at T s1 =200 K and T s2 =120 K. The former is of the second order from the ideal cubic pyrochlore structure with space group F d \bar3 m to a tetragonally distorted structure with I \bar4 m 2, while the latter is of the first order likely changing to another tetragonal space group I 4 1 22. We discuss the feature of the lattice deformation.