Structure Of CaF Research Articles

Effects of CeO<sub>2</sub> on Melting Temperature, Viscosity, and Structure of CaF<sub>2</sub>-bearing and B<sub>2</sub>O<sub>3</sub>-containing Mold Fluxes for Casting Rare Earth Alloy Heavy Rail Steels

Effects of CeO<sub>2</sub> on Melting Temperature, Viscosity, and Structure of CaF<sub>2</sub>-bearing and B<sub>2</sub>O<sub>3</sub>-containing Mold Fluxes for Casting Rare Earth Alloy Heavy Rail Steels

The structure of CaF 2(1 1 1) and BaF 2(1 1 1) single crystal surfaces: A tensor low energy electron diffraction study

The surface structures of the wide band-gap insulators CaF 2(1 1 1) and BaF 2(1 1 1) were investigated by means of low energy electron diffraction (LEED) with primary beam currents in the nA range. Beam intensities were recorded at 20 K sample temperature between 80 and 360 eV and analyzed using the tensor LEED approach. The results provide for the first time quantitative experimental information about the relaxation of these surfaces. The CaF 2(1 1 1) surface deviates only insignificantly from a truncated fluorite bulk lattice with F–M–F layer structure (M: Ca or Ba), the largest displacement being the inward shift of the topmost layer of fluoride anions by 0.03 ± 0.06 Å. The same contraction of the interlayer distance at the interface is significant for the BaF 2(1 1 1) surface, for which the topmost anion is displaced towards the bulk by 0.12 ± 0.07 Å. The positions of the alkaline earth metal cations as well as those of the second fluoride layer in this topmost F–M–F sheet are almost identical to their bulk values. The same holds for all deeper layers. From the temperature dependency of the diffraction intensities surface Debye temperatures Θ D,surface of 196 ± 19 K (CaF 2) and 125 ± 6 K (BaF 2) were deduced, respectively. The results suggest that the enhanced thermal motions are restricted to the topmost F–M–F layer only.

Hexaaquacobalt(II) bis(hypophosphite) and hexaaquacobalt(II)/nickel(II) bis(hypophosphite).

The title compounds, hexaaquacobalt(II) bis(hypophosphite), [Co(H(2)O)(6)](H(2)PO(2))(2), and hexaaquacobalt(II)/nickel(II) bis(hypophosphite), [Co(0.5)Ni(0.5)(H(2)O)(6)](H(2)PO(2))(2), are shown to adopt the same structure as hexaaquamagnesium(II) bis(hypophosphite). The packing of the Co(Ni) and P atoms is the same as in the structure of CaF(2). The Co(II)(Ni(II)) atoms have a pseudo-face-centred cubic cell, with a = b approximately 10.3 A, and the P atoms occupy the tetrahedral cavities. The central metal cation has a slightly distorted octahedral coordination sphere. The geometry of the hypophosphite anion in the structure is very close to ideal, with point symmetry mm2. Each O atom of the hypophosphite anion is hydrogen bonded to three water molecules from different cation complexes, and each H atom of the hypophosphite anion is surrounded by three water molecules from further different cation complexes.