X-ray powder diffraction and vibrational study of the solid solutions in (La 1− xRE x)OCl (RE=Gd and Y)

Abstract

The formation of cation solid solutions in the (La 1− x RE x )OCl (RE=Gd and Y) series was studied by vibrational (far-FTIR absorption and FT Raman scattering) spectroscopy and powder X-ray diffraction (XRD). The powder XRD data were further analysed by the Rietveld profile refinement method. The unit cell dimensions evolved linearly between 0⩽ x Gd⩽1 in the (La 1− x Gd x )OCl series. This solid solution retains the tetragonal PbFCl-type structure throughout the whole concentration range. In the (La 1− x Y x )OCl series, additional reflections were observed in the XRD pattern beyond x=0.5. With x=<0.7 this system has also the tetragonal structure but with higher yttrium concentration a separate phase is formed which was tentatively identified as the SmSI-type YOCl. The vibrational spectroscopy studies sustain the results obtained by XRD analysis. All six Raman-active and three of the four IR-active vibrational modes were observed. The energy of these modes evolved linearly in both (La 1− x Ln x )OCl solid solution series. The separate phase was observed for the (La 1− x Y x )OCl system by Raman spectroscopy, too.