Phase transitions in rare earth chlorides observed by XAFS

XAFS spectroscopy has increasingly been utilised to elucidate the nearest-n eighbour 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 Synchrot ron Radiation Facility (ESRF) are presented. The Fourier transformed radial structure functions, phi (r) show that the prominent peaks corresponding t o M-Cl (M: Nd or Dy) first shell contribution are shifted to shorter distan ces in the liquid melts as compared to those found in the corresponding sol ids. Similar behaviour has also been observed from other diffraction techni ques in typical ionic melts such as NaCl. From the temperature dependence o f the radial structure functions it is clear that the change in the M-Cl di stance on melting is much larger in NdCl3 than that in DyCl3.