Noticiero de Vigo : diario independiente de la mañana: Ano XXVII Número 11366 - 1912 outubro 26

This article reports on the identification, synthesis, and in-situ structure determination of a new crystalline calcium borosilicate compound of composition CaSi_1/3B_2/3O_8/3. Synthesis was carried out by complete crystallization on annealing from a corresponding glassy composition in the widely studied CaO–SiO₂–B₂O₃ ternary system. The crystallographic structure was determined ab initio using electron diffraction information and the charge flipping algorithm performed on synchrotron and neutron powder diffraction data collected in situ at high temperature. CaSi_1/3B_2/3O_8/3 is found to crystallize in the <i>Pna</i>2₁ (no. 33) orthorhombic space group, with <i>a</i> = 12.1025(4) Å, <i>b</i> = 5.2676(1) Å, <i>c</i> = 3.7132(1) Å, and <i>V</i> = 236.71(1) ų at 650 °C. Solid-state ²⁹Si and ¹¹B NMR experiments have confirmed the existence of finite chains along the <i>c</i> axis, formed by corner-sharing SiO₄ tetrahedra and BO₃ units. Silicon and boron species share a crystallographic site, and the Si/B distribution induces different possible arrangements of the chains which are discussed in light of DFT calculations. At room temperature, the existence of a superstructure, resulting from the ordering within nanoscale domains, was explored by transmission electron microscopy

Synthesis and Structure Resolution of RbLaF₄

The synthesis and structure resolution of RbLaF₄ are described. RbLaF₄ is synthesized by solid-state reaction between RbF and LaF₃ at 425 °C under a nonoxidizing atmosphere. Its crystal structure has been resolved by combining neutron and synchrotron powder diffraction data refinements (<i>Pnma,</i> <i>a</i> = 6.46281(2) Å, <i>b</i> = 3.86498(1) Å, <i>c</i> = 16.17629(4) Å, <i>Z</i> = 4). One-dimensional ⁸⁷Rb, ¹³⁹La, and ¹⁹F MAS NMR spectra have been recorded and are in agreement with the proposed structural model. Assignment of the ¹⁹F resonances is performed on the basis of both ¹⁹F–¹³⁹La <i>J</i>-coupling multiplet patterns observed in a heteronuclear DQ-filtered <i>J</i>-resolved spectrum and ¹⁹F–⁸⁷Rb HMQC MAS experiments. DFT calculations of both the ¹⁹F isotropic chemical shieldings and the ⁸⁷Rb, ¹³⁹La electric field gradient tensors using the GIPAW and PAW methods implemented in the CASTEP code are in good agreement with the experimental values and support the proposed structural model. Finally, the conductivity of RbLaF₄ and luminescence properties of Eu-doped LaRbF₄ are investigated

Synthesis and Structure Resolution of RbLaF₄

The synthesis and structure resolution of RbLaF₄ are described. RbLaF₄ is synthesized by solid-state reaction between RbF and LaF₃ at 425 °C under a nonoxidizing atmosphere. Its crystal structure has been resolved by combining neutron and synchrotron powder diffraction data refinements (<i>Pnma,</i> <i>a</i> = 6.46281(2) Å, <i>b</i> = 3.86498(1) Å, <i>c</i> = 16.17629(4) Å, <i>Z</i> = 4). One-dimensional ⁸⁷Rb, ¹³⁹La, and ¹⁹F MAS NMR spectra have been recorded and are in agreement with the proposed structural model. Assignment of the ¹⁹F resonances is performed on the basis of both ¹⁹F–¹³⁹La <i>J</i>-coupling multiplet patterns observed in a heteronuclear DQ-filtered <i>J</i>-resolved spectrum and ¹⁹F–⁸⁷Rb HMQC MAS experiments. DFT calculations of both the ¹⁹F isotropic chemical shieldings and the ⁸⁷Rb, ¹³⁹La electric field gradient tensors using the GIPAW and PAW methods implemented in the CASTEP code are in good agreement with the experimental values and support the proposed structural model. Finally, the conductivity of RbLaF₄ and luminescence properties of Eu-doped LaRbF₄ are investigated