Synthesis and X-Ray Diffraction Study of Potassium, Rubidium, and Cesium Polytungstates with Defect Pyrochlore and Hexagonal Tungsten Bronze Structures.-X-ray studies on the phase formation in M 2 WO 4 -WO 3 systems (M: K, Rb, Cs) verify the formation ofCs 6 W 11 O 36 and the existence of M 4 W 11 O 35 and M 2 W 7 O 22 phases. M 2 W 3 O 10 and Cs 6 W 11 O 36 possess a pyrochlore type structure whilst the structure of M 4 W 11 O 35 and M 2 W 7 O 22 resembles hexagonal tungsten bronze. Appropriate conditions for the solid phase synthesis and crystallization of discrete polytungtates from the corresponding alkali carbonate M 2 CO 3 and WO 3 are established. -(SOLODOVNIKOV, S. F.; IVANNIKOVA, N. V.; SOLODOVNIKOVA, Z. A.; ZOLOTOVA, E. S.; Neorg.

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A subsolidus triangulation of Li 2 MoO 4 -Rb 2 MoO 4 -MMoO 4 (M = Ca, Sr, Pb, Ba) systems is performed. The RbLiMoO 4 -Rb 2 M(MoO 4 ) 2 (M = Pb, Ba) joins, where 11 mol.% long Rb 2 M(MoO 4 ) 2 -based solid solutions are found, are studied in most detail. Ternary molybdates do not form in the systems, which is confirmed by spontaneous flux crystallization. The α-Rb 2 Pb(MoO 4 ) 2 crystals are obtained and their crystal structure is solved (а = 20.9724(15) Å, b = 12.1261(8) Å, с = 16.1171(10) Å, β = 115.728(13)°, С2/m space group, R = 0.0695, Z = 16), which is a monoclinic superstructure of the palmierite type and has the largest cell volume and the most complex structure among lead-containing palmierites. One of the MoO 6 tetrahedra is orientationally disordered over two sites; lead atoms are shifted from the centers of their coordination polyhedra to one of their faces and have cn = 6-8; for rubidium cations cn = 10-12.

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