Structural phase transition of an intercalation compound Mn1/4NbS2

A structural phase transition of an intercalation compound Mn1/4NbS2 has be en investigated by X-ray diffraction at high temperatures. The lattice para meter c exhibited a discontinuous change at 640K. The superlattice reflecti ons observed below 640K disappeared suddenly above 640K. The phase transiti on at 640K took an aspect of the first-order phase transition. The precise structure analyses were performed at various temperatures above and below t he phase-transition temperature. It was revealed that Mn atoms were arrange d in disorder in the high-temperature phase, while the Mn atoms were ordere d forming the 2a(0) x 2a(0) x c(0) superlattice in the low-temperature phas e. The Nh 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.