Observation of a second-order distortion in Nd₃Co₄Sn₁₃

In this paper we report the resistivity and neutron scattering experiments on Nd₃Co₄Sn₁₃. These results indicate that Nd₃Co₄Sn₁₃ undergoes a structural distortion from a high-temperature primitive cubic unit cell to an I-centered superstructure and a concomitant doubling of the lattice constant. The P m -3 n structure of Yb₃Rh₄Sn₁₃ describes well the neutron powder diffraction pattern collected at room temperature, but failed to fit the low–temperature profiles due to the presence of (h/2 k/2 l)-type diffraction peaks. Single crystal elastic neutron scattering performed in the [h h l] scattering plane shows the lattice distortion with mean field character at 124 (2) K as the temperature is lowered. Besides, three I-centered space groups are excluded by the single crystal diffraction work, including I -4 3 d symmetry which is observed in other R₃T₄Sn₁₃ compounds.