A HIGH-RESOLUTION NEUTRON POWDER DIFFRACTION STUDY OF NEODYMIUM DOPING IN BARIUM CERATE

High-resolution neutron powder diffraction data have been collected on 6 perovskites of composition BaCe1-xNdxO3-x/(2), with 0 less than or equal to x less than or equal to 0.2, in which structural phase transi tions Pmcn-->P4/mbm at x=0.05, and P4/mbm-->Pm3m at x=0.1, were inferr ed from a recent Raman spectroscopy study. Our results contradict thes e conclusions; for 0 less than or equal to x less than or equal to 0.1 6, BaCe1-xNdxO3-x/2 is orthorhombic, space group Pmcn. At x=0.2, the p owder data are consistent with either space group Pmcn or Cmcm, and co uld not be distinguished using structural-model-free fits due to incre ased line broadening present in this sample. The smaller number of ref lections in space group Pmcn favours this space group for x=0.2. The d eviation from cubic symmetry has been determined from a calculation of the scalar spontaneous strain, assuming that the dopant-dependent eff ects in the thermal expansion properties are small in BaCe1-xNdxO3-x/2 . The spontaneous strain decreases with increasing neodymium doping sh owing the deviation from an ideal cubic aristotype reduces with doping level. There is some evidence for saturation in the spontaneous strai n at x>0.2.