GROWING OF SINGLE-CRYSTALS OF DOUBLE SODIUM-MANGANESE(II) PYROPHOSPHATE.

Single crystals of Na₂Mn₃(P₂O₇)₂ compound have been first obtained during the examination of interaction in the Na₂O-P₂O₅-Mn₂O₃-NaF (10 wt.%.) system in the fluxes with Na₂O:P₂O₅ molar ratios ranging from 0.52 to 0.76 (saturated with manganese(III) oxide 25.0-32.0 wt.%) at the temperatures of 960-880°C. Optimum conditions for the synthesis and growing of single crystals of Na₂Mn₃(P₂O₇)₂ compound have been determined. Complete X-ray diffraction analysis of the synthesized phosphate Na₂Mn₃(P₂O₇)₂ has been performed. According to its structure, the double phosphate Na₂Mn₃(P₂O₇)₂ belongs to the triclinic crystal system, spatial grid P1; lattice parameters are as follows: a=5.359 Å, b=6.563 Å, c=16.299 Å, α=81.29°, β=82.70°, γ=72.44°, V=538.23 ų, Z=4, C_calc= 3.447 g cm^-3. Structural features of synthesized phosphate have been determined. The structure is composed of continuous chain of distorted octahedra [MnO₆] spacing along the direction ob. Diphosphate groups of tetrahedra [PO₄] divide the chains [MnO₆] and also run along ob direction. Pairwise linked pentagonal bipyramids of sodium divide the «units» of polyhedral of manganese and phosphorus, filling the channels along oy axis. The crystalline structure of Na₂Mn₃(P₂O₇)₂ includes three nonequivalent, according to their crystallography, octahedra of manganese with slightly distorted form. The compound has been studied using X-ray diffraction and X-ray phase analyses, differential thermal analysis, IR spectroscopy and complete chemical analysis. [ABSTRACT FROM AUTHOR]