X-ray diffraction study of V₃Si and V₃Ge

Abstract

A double superconducting transition in a single crystal of V₃Si was reported by Dayan and co-workers. We have measured lattice parameters of a sample of this material down to about 8 K with the use of x rays. The crystal is found to contain two kinds of regions having room-temperature lattice parameters differing by about 300 ppm, and we believe the regions have different Si concentration. One kind of region undergoes the martensitic transformation, while the other does not. The nontransforming region shows a negative thermal expansivity below about 40 K, in contrast to the transforming region. We have also measured the lattice parameter of V₃Ge (which does not undergo a martensitic transformation) and it shows a negative thermal expansivity below about 35 K. We discuss how these and other reported differences between transforming and nontransforming samples could be explained.