Crystal structure of LiLnW2O8 (Ln=lanthanides and Y): An X-ray powder diffraction study

Crystal structures that occur in LiLnW2O8 (Ln=lanthanides and Y) have been studied using Rietveld profile analysis of X-ray diffraction data. Two types of structures were observed. The scheelite structure of the space group I41/a is adopted for compounds containing large lanthanides Ln=La–Gd. For smaller lanthanides (Ln=Dy–Lu and Y) the wolframite structure with the space group P2/n is observed. In LiTbW2O8, both structures occur. The phase transition between the two is a slow process making the obtainment of pure low temperature phase (wolframite) difficult. The space groups P1̄ and P2, recently reported for LiEuW2O8 and LiYW2O8, have not been observed in this series of compounds.

Part of the X-ray diffraction patterns of LiSmW2O8 and LiDyW2O8 representing two structure types in LiLnW2O8: the scheelite with Ln=La–Gd and wolframite with Ln=Dy–Lu and Y. In LiTbW2O8 both the scheelite and the wolframite structures occur at high and low temperatures, respectively..Figure optionsDownload as PowerPoint slideHighlights
► Double tungstates of the formula LiLnW2O8 (Ln=lanthanides and Y) were systematically synthesised and their crystal structures were determined.
► LiLnW2O8 adopt either the scheelite structure (I41/a) (Ln=La–Gd) or wolframite structure (P2/n) (Ln=Dy–Lu and Y).
► Both structures occur in LiTbW2O8 and the I41/a→P2/n phase transition is a slow process.
► The space groups P1̄ and P2 recently reported for LiEuW2O8 and LiYW2O8 were not observed.