Synthesis and Some Properties of Tungstophosphatozincates and Their Thermolysis Products

Russian Journal of General Chemistry - Tungstophosphatozincates with the Keggin anion structure Kt5[PW11O39Zn(H2O)]?nH2O, Kt = Rb+, Cs+, (CH3)4N+; (C2H5)4N+ were synthesized. Their...     

Isomorphous substitution of samarium and gadolinium for calcium in hydroxyapatite structure

Isomorphous substitution of samarium and gadolinium for calcium in synthetic hydroxyapatite by the scheme Ca²⁺ + OH⁻ → Ln³⁺ + O²⁻ was studied by X-ray powder diffraction and IR spectroscopy. The homogeneity region of Ca_{10 − x} Ln _x (PO₄)₆(OH)_{2 − x} O _x phases of variable compositions synthesized at 1100°C was found to exist up to x of 1.8 for Sm and 1.4 for Gd. In the heterogeneous region of solid solutions, phases with Ln₃PO₇ and LnPO₄ structures were formed. The structures of some solid solutions were refined by the Rietveld method, which allowed us to establish that the substitution of Ln³⁺ ions for Ca(2) positions is preferred. Changes in the intensities of the absorption bands of stretching and libration vibrations of OH groups are indicative of a partial dehydration of oxyhydroxyapatite. The substitution was shown to decrease Ca(2)-O(OH) and P-O distances and increase Ca(2)-O(1,2,3) distances.     

Numerical analysis of the diffraction of a plane wave on a periodic grating of loaded strip elements

Translated from Aktual'nye Voprosy Prikladnoi Matematiki, pp. 138–144, 1989.