CONDITIONS OF FORMATION AND PHYSICO-CHEMICAL CHARACTERISTICS OF LITHIUM COORDINATION NITRATES OF LANTANOIDES LI3[LN2(NO3)9]∙3H2O (LN–LA–ND)

Abstract

Single-crystal samples were synthesized and a complex physicochemical characterization of the lithium coordination nitrates of the rare-earth elements of the cerium subgroup of the isostructural series Li 3 [Ln 2 (NO 3 ) 9 ]∙3H 2 O (Ln – La–Nd) was carried out in order to obtain reliable knowledge of the joint behavior of the constituent components and features of transformations in the systems of nitrate precursors during the formation with thermal activation (25–1000  o C) of multicomponent oxide REE-containing functional materials for various purposes with structure perovskite, garnet according to modern technologies with reproducible perfect stable properties. It has been revealed that the structure of this type of compounds is based on rare-earth oxygen polyhedra in one way or another connected in space. Ln 3+ ions play a dominant role in the complexation process, showing high coordination numbers of 12. The individuality of Ln-complexes in coordination nitrates is manifested: in a limited set of Ln-polyhedra; in the tendency of the complexing ion to create around itself a symmetrically organized coordination sphere; that the complexes with different composition and stoichiometry may correspond to the same, although significantly distorted coordination polyhedra. Li + cations in the structure formation of alkaline rare-earth nitrates can have a significant effect on the shape of Ln 3+ -polyhedra and on the spatial packing of their construction. The data obtained give a good reason to assume that the process of decomposition of crystalline alkaline rare-earth nitrates in technological objects during thermal activation begins with the breaking of alkaline metal-oxygen bonds. This fact is confirmed by the results of studies on the behavior of the above compounds in the range of 25–1000 °C by thermographic means. Thermograms of the samples are characterized by two, in addition to the initial state, temperature ranges of mass stabilization, corresponding to the formation of anhydrous complex nitrates and their thermolysis products at temperatures above 900 °C. The predominant phase of the final products is – LiLnO 2 .