G. Blasse

NEW COMPOUNDS WITH PEROVSKITE-LIKE STRUCTURES

Abstract A number of mixed metal oxides with perovskite-like structures are reported. On the sublattice of the smaller cations 1:1 and 1:2 long-range order have been found in the perovskite as well as in the hexagonal barium titanate structure. The Jahn-Teller distortions of these compounds are discussed. Finally the energy terms stabilizing the hexagonal barium titanate structure relative to the perovskite structure are considered. It seems probable that anion polarization and not cation-cation bonding stabilizes the hexagonal barium titanate structure.

Qualitative approach to the structural differences between some mixed metal oxides containing Sb5+, Nb5+ and Ta5+

Abstract The structural differences between a number of mixed metal oxides containing Sb5+, Nb5+ and Ta5+ ions are discussed in terms of the following three starting-points: 1. (a) the pentavalent metal ions will be as far from each other as possible due to Coulomb repulsion; 2. (b) an asymmetrical positive charge distribution around the anion favours polarization and covalency effects; 3. (c) a kind of metal ion-metal ion bond is possible between highly-charged metal ions with noble-gas configuration. Applications to several types of compounds are considered.

Structure and Eu3+-fluorescence of lithium and sodium lanthanide silicates and germanates

Abstract The preparation of a series of new compounds NaLnSiO4 and NaLnGeO4 (Ln stands for one of the lanthanides or yttrium) is described and the results of an X-ray powder diffraction investigation of these materials are presented and discussed. Three different structure types are found for these compounds, viz. olivine, β-K2SO4 and an unknown structure. The compounds ALnBO4 (A  Li, Na, B  Si, Ge, Ln  La, Gd, Y or Lu) have been doped with the Eu3+ ion. The fluorescence of these phosphors is also reported. The spectral energy distribution of the emission gives some more information on the crystal structures. The variations of the excitation spectra and efficiencies with the crystal structure obey to correlations given by us before.

Crystal structure and fluorescence of compounds Ln2Me4+Me6+O8

Abstract The crystal structures of compounds Ln 2 Me 4+ Me 6+ O 8 are reported (Ln = La, GD, Y or Lu; Me 4+ = Si, Ge or Ti; Me 6+ = Mo or W). Nearly all of these compounds have the scheelite structure or the fergusonite (distorted scheelite) structure. A remarkable exception is Y 2 SiMoO 8 , which has zircon structure. In this compound the Si 4+ and Mo 6+ ions are long-range ordered. The fluorescence of the Eu 3+ ion in these host lattices was also investigated. The super structure of Y 2 SiMoO 8 was confirmed by the spectral energy distribution of the Eu 3+ ion in this lattice. The emission spectra of the scheelites point to a considerable degree of order in the case of Me 4+ = Si. The low efficiency of the fluorescence is discussed. The fluorescent of the unactivated host lattices and of Bi 3+ and Tb 3+ ions in these lattices is dealt with.