GADOLINIUM(III) COMPLEX OXIDE COMPOUNDS OF OBTAINED FROM MOLYBDATE-PHOSPHATE MOLTEN SALT

The peculiarities of K2Gd(PO4)(MoO4) single crystal growth from combined phosphate-molybdate melts have been investigated. formation regions GdPO4, KGd(MoO4)2 and their cocrystallization fields with the mixed anionic compound potassium – gadolinium established. IR spect­roscopy showed that in all compounds molybdenum phosphorus are a tetrahedral environment, phase composition was confirmed by X-ray powder. Crystallization target is observed pseudobinary section K2Mo2O7-KPO3 orthiorombic system, space group Ibca, Z = 8, а 19,694(4) Å, b 12,260(3) c 6,961(3) Å. Double phosphate K3Gd(PO4)2 crystallizes form colorless prismatic crystals initial ratio K/P 1.7–3.3, which practically corresponds to K2MoO4 K4P2O7. Phosphate GdPO4 up 0.1 mm size at maximum KPO3 content melt, 0.20–0.50 K/(Mo+P) 0.25–0.33. Crystal-chemical criteria for mixed-anion-type layered frameworks, island structures, three-dimensional frameworks based on systems rare earth elements proposed. key factor complex oxide molybdate-phosphate K/Mo solution - melt: 1) 0.5–1.1, LnPO4 orthophosphates formed, characterized 3D framework basis LnO7/LnO8poly­hedra condensed into framework; 1.2–1.5, K2Ln(PO4)(MoO4) (Ln Gd- Tb) structure where LnО8 forms zigzag chains; 3) 1.6–3.0, double K3Ln(PO4)2 an formed.