Cristaloquímica de calcogenuros metálicos con estructuras complejas, de maclado químico y moduladas

Abstract

The study on rare earth chalcogenides (sulphides, selenides and tellurides) is an active areanowadays. The structural study of these compounds is interestingly because, even the binarysystems, present a great complexity, finding simple stoichiometries, polymorphism, grotesquestoichiometries and solid solutions. Moreover, the structural types exhibited by these compoundsare not only those of the oxides but also they present particular ones. For this reason, thedescription and understanding of these structures, as well as their relationship and the relationshipwith others simpler structures is a wide and active research field.The main goal of this thesis is the crystallographic and crystal-chemical study and the micro andnanostructural characterization of complex chalcogenides, mainly by transmission electronmicroscopy and the associated analytical techniques. Besides, X- ray powder diffraction datawere employed to refine the average unit cell parameters previously determined ‘directly’ bymeans of conventional or selected area electron diffraction (SAED).In the binary system Tm-S, the polymorphs Tm2S3 - I, II and V (δ - Ho2S3, Tm2S3 and α - Al2O3types respectively) have been synthesized by solid-gas reactions. Here we report, for the firsttime, the synthesis of the polymorph Tm2S3 - II under normal pressure conditions and thepolymorph Tm2S3 - V at a temperature (T = 1173 K) well below the reported in the literature forthis compound. The polymorph Tm2S3 - III (Bi2S3 type) was obtained at high-pressure conditionsand the addition of CS2 during the high-pressure synthesis lead to the polysulphide TmS2 (PbClF– type) and new superstructures of this high-pressure phase (a = b = 4 x d (102) TmS2 = 1.09 nmand c = 3xd (010) TmS2 = 1.14 nm)...