Band 146, Heft 1-3

The normal modes of vibration of various alkali feldspars were calculated on the basis of a simple harmonic valence force field. Infrared and Raman spectra were recorded over the whole frequency range. With 7 force constants for ordered feldspars and 5 constants for disordered feldspars the calculated frequencies could be fitted with an average deviation of 10–16 cm −1 , depending on the compound. The fitting was done by a least-squares method. The model used cannot explain the frequency shifts which are observed in going from an ordered to a disordered Si/Al distribution.

For the low-symmetry system of the ion-exchanger zirconium phosphate the influence of irradiation and ion-exchange on the crystal disorder has been investigated by means of photographic x-ray diffraction methods. The weakening and the shifting of Bragg reflections and the broadening of maxima of diffuse scattering allow the estimation of the concentration and the strength of defects induced in this system.

After drying zirconium phosphate Zr(HPO 4 )(NaPO 4 ) · 5H 2 O yields two compounds with a law of intergrowth. One of these is not stable and converts into the other, Zr(HPO 4 ) (NaPO 4 ) · H 2 O, within a few months. Both phosphates, Zr(HPO 4 ) (NaPO 4 ) · H 2 O and Zr(HPO 4 ) 2 · H 2 O, are influenced by γ irradiation at room temperature. The annealing in terms of decreasing cC 2 of defect concentration and defect strength have been measured by means of x-ray photographic methods.

The crystal structure of synthetic bicchulite was determined with single-crystal x-ray methods ( R = 0.07 for all 65 observed reflections). Bicchulite has a sodalite-type framework structure with Al and Si distributed statistically in the tetrahedral sites, coordinated solely by oxygen atoms. Calcium is coordinated octahedrally by three oxygen atoms and three OH groups. Four such octahedra are linked to a group by OH–OH edges. These octahedra groups occupy the cavities within the framework.

NaAsS 2 is monoclinic, P 2 1 / c , a = 5.867(2) Å, b = 11.305(3) Å, c = 5.586(2) Å, β = 92.95(2)°, Z = 4. The structure has been determined from three-dimensional x-ray data collected by counter methods, and refined by least-squares to a final conventional R value (on F) of 0.0311 for 651 measured reflections. The structure can be considered as an ordered derivative of the NaCl type, and is similar to the structure of BaSnS 2 . A salient structural feature is the presence of infinite chains of composition AsS 2 which run in the direction of c axis. The metal ordering observed in this structure is different from that present in KSbS 2 , which is a NaCl ordered derivative structure as well.

Yb 2 Ca 3 [BO 3 ) 4 can be obtained metastably at room temperature by quenching from temperatures between 1275°C (melting point) and 1155°C (temperature of decomposition in Yb[BO 3 ] and a still unknown phase). The space group of the colourless, prismatic crystals is P 2 1 cn ( Z = 4); lattice constants, morphological and optical data are presented.

Crystals of calciumdiborate, CaB 4 O 7 were prepared by devitrification of a glass of the composition CaO · 3B 2 O 3 . The compound is monoclinic, space group P 2 1 / n . The lattice constants are a = 12.26 4 Å, b = 9.89 5 Å, c = 7.79 6 Å, β = 91.26° and Z = 8.

Abstraft La 3 Ca 3 [BO 3 ] 5 is hexagonal with the lattice constants a = 10.51 9 Å, c = 6.41 1 Å and Z = 2. The space group is P 6 3 mc , P [unk]2 c or P 6 3 / mmc . The compound probably is isostructural with burbankite, A 3 B 3 [CO 3 ] 5 with A = (Na,Ca) and B = (Ca, Sr, Ba, RE). La 3 Ca 3 [BO 3 ] 5 melts incongruently at 1135°C (decomposition into La[BO 3 ] and La 2 Ca 3 [BO 3 ] 4 ).

Taeniolite, KLiMg 2 Si 4 O 10 F 2 , was synthesized from a mixture of KF, LiF, MgO and SiO 2 , and the crystal structure was refined with three-dimensional x-ray diffraction data. The crystals are monoclinic (1 M type) with the space group C 2/ m , a = 5.231(1), b = 9.065(2), c = 10.140(1) Å, β = 99.86(2)°, and Z = 2. Refinements with the full-matrix least-squares procedure gave the final R value of 0.024 for 1303 observed reflections. All the bridging Si–O distances are 1.638(1) Å, whereas the nonbridging one is 1.586(1) Å. A comparison of several 1 M-type micas clearly indicates the effect of octahedral cations on the distortion of (Si,Al)O 4 tetrahedra. Li + ions are more concentrated at the M(2) site than at M(1) in conformity with the size difference between the coordination octahedra. The ditrigonal distortion of the tetrahedral sheets is still smaller than that of KMg 2.5 Si 4 O 10 F 2 , having the tetrahedral rotation angle α of 1.08°. The octahedral flattening angles, ψ are 57.8° and 57.9° for M(1) and M(2) sites, respectively.

Lattice constants of KN 3 , Sr(N 3 ) 2 and of a new K,Sr azidebydrate have been measured at 20° and −180°C using a low-temperature powder diffractometer. Thermal expansion coefficients have been calculated.