Synchrotron powder diffraction study of the low‐temperature lattice distortion of PbMo6S8

Synchrotron and Guinier x‐ray powder diffraction data as a function of temperature on a superconducting PbMo6S8 sample (Tc=14.7 K) showed evidence for a subtle structural phase transition at Tl=140 K, leading from a rhombohedral high‐temperature to a triclinic low‐temperature modification. The transition is incomplete and presents a hysteresis of about 110 K. The triclinic cell parameters obtained at 130 K, a=6.534(9) A, b=6.532(9) A, c=6.529(9) A, α=89.27(8)°, β=89.12(8)°, γ=88.97(8)°, show that the distortion affects mainly the angles (δα/αr=0.3%) and less the edges (δa/ar