C.M. Foris

Structure and luminescence of the orthorhombic LnWO4Cl-type rare earth halo tungstates

Abstract LaWO 4 Cl is representative of a series of Ln WO 4 Cl compounds in which Ln can be La to Sm. LaWO 4 Cl crystallizes in orthorhombic Pbcm symmetry, and its structure was refined using a disordered model to an R value of 4.0%. The most unusual structural feature is the 5-coordination of the W atom in the form of a trigonal bipyramid. The La atom is 9-coordinated. Luminescing ions, such as Sm, Tb, and Eu, were introduced into LaWO 4 Cl as a host, and their excitation and emission spectra are reported. The Raman spectrum of LaWO 4 Cl is compared to those of compounds containing W in more common tetrahedral and octahedral environments. X-Ray powder diffraction data are also reported.

X-ray study of the PbCl2−xIx and PbBr2−xIx systems

Abstract Compounds from the systems PbCl 2 PbI 2 and PbBr 2 PbI 2 were examined by x-ray diffraction. The lattice parameters of these phases are presented and the refined crystal structures of the intermediate compounds PbClI and PbBr1.2I0.8 are reported. Both structures have Pbnm symmetry, are isostructural with PbCl2, and have the different halogens ordered in the two Cl sites. Phase studies showed that PbCl2 and PbClI have practically no mutual solubility, while PbBr2 and PbBr1.2I0.8 have appreciable solubility ranges, particularly for PbBr2-rich concentrations. At least 17% Br is present in the I site of PbBr1.2I0.8. Nevertheless, it is a distinct phase with miscibility gaps toward PbBr2 and PbI2. This behavior is explained by the size disparity between the halogens. The intermediate phases do not form solid solutions with hexagonal PbI2.

Pr3NbO4Cl6: A new praseodymium chloro niobate

Abstract Pr 3 NbO 4 Cl 6 crystallizes in the hexagonal space group P 6 3 m with a = 12.714(3) and c = 3.962(2) A . The structure was refined using 420 diffractometer intensities to a final R value of 1.7%. The crystal structure consists of an infinite network of NbO 5 and PrO 2 Cl 7 polyhedra. The powder diffraction pattern is also reported.

The crystal structure of Pb8Bi2(PO4)6O2

Single crystals of Pb8Bi2(PO4)6O2 were grown by the Czochralski technique, and the structure of this compound was determined. It was found to crystallize in Pnma orthorhombic symmetry with a = 13.313, b = 10.284 and c = 9.219 A. The structure was refined to an R value of 7%. Powder diffraction data are also reported.

Structure and luminescence of the monoclinic LnWO4Cl-type rare earth halo tungstates

GdWO4Cl is representative of a series of LnWO4Cl compounds where Ln can also be: Eu, Tb, Dy, Ho, Er, Tm and Y. These compounds crystallize in monoclinic C2/m symmetry, and the structure has been refined to R = 5.0% for GdWO4Cl. Luminescing ions such as Eu+3 and Tb+3 have been incorporated into GdWO4Cl and a Raman spectrum was recorded.

BiPbVO5 — A new bismuth lead vanadate

BiPbVO5 was prepared for the first time and single crystals were grown by the Czochralski technique. Precession x-ray photographs indicated triclinic symmetry with space group 1 or 1. The lattice parameters are a = 7.082 A, b = 7.802 A, c = 5.203 A, a = 111.788 deg., β = 95.207 deg., γ = 108.717 deg.

Structure and luminescence of the α-LnNb3O9-type rare earth niobates

..cap alpha..-LnNb/sub 3/O/sub 9/ (Ln = La, Pr, Nd) compounds have been prepared hydrothermally from acidic solutions. In comparison to the previously reported orthorhombic ..beta.. modifications, ..cap alpha..-LnNb/sub 3/O/sub 9/ compounds are monoclinic. The structure of ..cap alpha..-PrNb/sub 3/O/sub 9/ was determined with a = 5.3784(6), b = 7.602(2), c = 16.344(2) A, and ..beta.. = 92.21(1)/sup 0/, space group Ps/sub 1//c. It is built of double and single chains of cornershared NbO/sub 6/ octahedra extended along the b axis. Praseodymium atoms reside in tunnels along the b axis and are in eight-coordination with oxygen. All ..cap alpha..-LnNb/sub 3/O/sub 9/ compounds can be irreversibly converted to the ..beta.. modification by heating in air to 1200/sup 0/C. The X-ray excited luminescence of Sm-, Eu-, Tb-, and Dy-doped ..cap alpha..-LaNb/sub 3/O/sub 9/ is also reported. 11 references, 3 figures, 5 tables.

Refined cell parameters of the Ln2WO6-type rare earth tungstates

Rare earth tungstates of the stoichiometry Ln2WO6 where Ln = Ce to Lu have been prepared and their lattice parameters were refined by a least-squares method. They have two structures: the C2c symmetry for the compositions Ce2WO6 through Ho2WO6, and a monoclinic group from Er2WO6 to Lu2WO6 crystallizing most likely in the P2m or P21m structure. High pressure modifications are described for Dy2WO6 and Ho2WO6.

Crystal growth and properties of lead pyrophosphate, Pb2P2O7

Abstract Single crystals of Pb2P2O7 have been grown by the Czochralski technique. They have the triclinic space group P 1 with cell dimensions a = 6.9627 A, b = 6.9754A, c = 12.764 A, α = 96.78°, β = 91.16°, γ = 89.68°. There are four molecules per unit cell. Dielectric properties for this compound have been measured and are discussed.

LiPbPO4, a new lithium lead phosphate

LiPbPO4 was prepared for the first time and single crystals of the compound were grown by the Czochralski technique. The composition crystallizes in the noncentric space group Pna21 (Point group mm2) with a = 7.980 A, b = 18.64 A and c = 4.938 A.