Phase transitions in rare earth chlorides observed by XAFS

XAFS spectroscopy has increasingly been utilised to elucidate the nearest-neighbour structure in the condensed phases. In this paper, the XAFS spectra of NdCl₃ and DyCl₃ in both the solid and the liquid phases measured at the Nd and Dy LIII absorption edges on beam line BM29 of the European Synchrotron Radiation Facility (ESRF) are presented. The Fourier transformed radial structure functions, φ(r) show that the prominent peaks corresponding to M-Cl (M: Nd or Dy) first shell contribution are shifted to shorter distances in the liquid melts as compared to those found in the corresponding solids. Similar behaviour has also been observed from other diffraction techniques in typical ionic melts such as NaCl. From the temperature dependence of the radial structure functions it is clear that the change in the M-Cl distance on melting is much larger in NdCl₃ than that in DyCl₃.