Ab Initio Determination of the Novel Perovskite-Related Structure of La7Mo7O30from Powder Diffraction

Polycrystalline samples of BaCexZr1-xO3were prepared by solid state reaction. X-ray diffraction measurements show that all compounds are single-phase and XRD patterns can be indexed on the basis of the ideal perovskite structure. However, Raman data show that BaCexZr1-xO3exhibits slightx-dependent distortions from the ideal perovskite structure. Indeed the evolution of Raman spectra of BaCexZr1-xO3, asxdecreases at room temperature or as temperature increases for a givenxvalue, is similar to the evolution of Raman spectra of BaCeO3as temperature increases. These observations lead us to propose a phase diagram in the binary system BaCeO3–BaZrO3based on the known structures of BaCeO3(Pnma, Imma, R c, andPm3m).