Structural Analysis of Spinel Compound CuV₂S₄ with Incommensurate Modulation

Abstract

We have investigated the incommensurate crystal structure of the spinel CuV₂S₄, which exhibits incommensurate charge-density wave at 90 K, using the synchrotron powder diffraction technique. It is found that the crystal structure at 70 K has an orthorhombic unit cell with the superspace-group Imm2（0β0）with a modulation vector q＝0.7391（5）b*. By Rietveld analysis including the incommensurate modulation along the b-axis, large static atomic displacements were found at the positions of V atoms, suggesting that V atoms play an important role in a charge-density wave transition. We have found the formation of V clusters, and arrangements of the clusters form a gradation pattern along the b-axis.