Local Structure Instability Across the Martensitic Transition in Nb3Sn

We report x-ray absorption fine structure (XAFS) measurements at the Nb K -edge of a Nb 3 Sn single crystal, for temperatures across the martensitic structural transition temperature T m . The Fourier transform amplitude of the peak associated with the second neighbor Nb–Nb and Nb–Sn pairs exhibits hysteresis across the martensitic transition under cooling and heating the sample across the transition. In contrast no such behavior was found for the Nb–Nb nearest neighbor distribution. The observed hysteresis can be attributed to the second neighbor Nb–Nb pairs as only the Debye–Waller factor of these pairs exhibits such a behavior. These results are consistent with a first-order phase transition, which has been previously proposed, and which suggests the possibility of an inhomogeneous ground state similar to other high-temperature superconductors.