COMPOSITION, CRYSTAL STRUCTURES, THERMAL STABILITY OF NEW TERNARY POTASSIUM-CONTAINING MOLYBDATES. R.F.Klevtsova, L.A. Glinskaya, Zh.G. Bazarova, P.V. Klevtsov, Institute of Inorganic Chemistry, Novosibirsk, Russia
The K2MoO4 - AMoO4 - Zr(MoO4)2 (A=Mg,Mn) systems were investigated by using quasibinary sections and new phases, ternary molybdates of different compositions (I - K(Mg0.5Zr0.5) (MoO4)2; II -K0.6(Mn0.9Zr0.9) (MoO4)3 III - K5(A0.5Zr1.5) (MoO4)6 ), were established to exist there. Single crystals were prepared by spontaneous flux crystallization and studied by an X-ray structure analysis (KUMA and CAD 4 diffractometers, Mo K radiation). Some crystallographic data are given in the table.
Sp.gr. a c Z dx R
I P3(-)m1 5.763 7.187 1 3.348 0.022
II R3(-)c 9.474 24.371 6 3.336 0.046
III-Mg R3c 10.576 37.511 6 3.576 0.026
III-Mn R3c 10.584 37.576 6 3.606 0.027
The compounds were shown to fall into three different structure types: (a) glaserite (I); (b) NASICON (II); (c) -Ca3(PO4)2 (III). These are built up on the base of three-dimensional frameworks of MoO4 tetrahedra and MO6 octahedra with the potassium atoms in the voids. All structures investigated have the following characteristic: a statistic filling of M octahedral positions by the Mg( or Mn) and Zr atoms. Structural peculiarities (size, shape, site occupancy and modes of joint of the coordination polyhedra) were used to interpret physical properties. The comparative crystal chemical analysis of the investigated and related compounds has been carried out. The thermal analysis showed that all compounds melt incongruently at 550-700oC. Polymorphism has not been revealed in the crystals.