Intercalation compounds of alkali metals with niobium and tantalum dichalcogenides

Abstract The preparation, crystal structures and some properties of the compounds Aitp,mx2 are reported, where A = Li, Na, K; M = Nb, Ta; X = S, Se. The compounds were prepared by heating mixtures of the elements or by heating mixtures of the alkali metals with the dichalcogenides, MX2. The selenides prepared were homogeneous only for p ≈ 2 3 , for some of the sulfides a homogeneity range from about p = 0.4 to 0.7 was found. The compounds ApMX2 are thermally stable; in moist air they are slowly hydrolized with formation of hydrogen sulfide or selenide. The compounds ApMX2 are hexagonal; the alkali metals are situated between MX2 slabs. The coordination of M( = Nb, Ta) is trigonal-prismatic in all the compounds. The coordination of Na and K is also trigonal-prismatic in the selenides and in most of the sulfides, but in some polymorphs of the sulfides the coordination of the alkali metals may be octahedral. The occurrence of trigonal-prismatic coordination is discussed.