X-ray study of superlattice melting in TiS2Ag0.33

We report the results of a detailed x-ray-scattering study of the layered intercalation compound TiS2Ag0.33. Below room temperature, the Ag atoms form a three-dimensional commensurate superlattice with 3×3R30°ordering within Ag layers and a stacking sequence. This stacking sequence puts the Ag superlattice ordering into the universality class of the three-dimensional XY model and hence represents a classic example of what has been called "continuous melting in three dimensions." © 1982 The American Physical Society.