Structural phase transition of an intercalation compound Mn1/4NbS2

A structural phase transition of an intercalation compound Mn1/4NbS2 has been investigated by X-ray diffraction at high temperatures. The lattice parameter c exhibited a discontinuous change at 640 K. The superlattice reflections observed below 640 K disappeared suddenly above 640 K. The phase transition at 640 K took an aspect of the first-order phase transition. The precise structure analyses were performed at various temperatures above and below the phase-transition temperature. It was revealed that Mn atoms were arranged in disorder in the high-temperature phase, while the Mn atoms were ordered forming the 2a0×2a0×c0 superlattice in the low-temperature phase. The Nb and S atoms around the ordered Mn atoms slightly shifted from the high-symmetry position in the low-temperature phase. The order parameters were the degree of order of the Mn atoms and the degree of displacement of the Nb and S atoms.