X-ray and electron diffraction studies of the structures of pseudo-perovskite compounds lead scandium tantalate (Pb2(Sc,Ta)O6) and lead magnesium tungstate (Pb2(Mg,W)O6)

摘要

Electron diffraction patterns, x-ray precision patterns and synchrotron Rietveld powder diffraction profiles were used to study the crystal structure of the pseudo-perovskite compd. Pb2(Sc,Ta)O6 (PST). The results of a Rietveld refinement and single-crystal x-ray precision studies showed that PST has a lower symmetry than the cubic Fm3m in the paraelec. state. The remarkable similarities between the crystal structures of the antiferroelec. Pb2(Mg,W)O6 (PMW) and ferroelec. PST were studied in detail by electron diffraction and it is suggested that PST is a weak or frustrated antiferroelec. oxide. The influence of the degree of structural long-range order on the existence of an antiferroelec. phase transition in PST and PMW is discussed. [on SciFinder(R)]