Features of phase composition of non-stoichiometric fluoride systems based on rare earth metals

Rare earth metals and compounds based on them are widely used to produce various composite materials. An interesting approach is to create multicomponent modifiers that have several elements as a matrix in equal equiatomic proportions. A feature of multicomponent fluoride systems is that they have a high entropy of mixing. For the synthesis of fluorides, high-purity oxides with a base substance content of at least 99.99% were used. An important requirement for the obtained rare-earth fluoride powders is single-phase. The article presents a study of the structural-phase state and a quantitative phase analysis of a multicomponent fluoride system of the structural type of tisonite (LaF₃) with rare earth elements: LaF₃-SmF₃-GdF₃-ErF₃-ScF₃. Rare earth metals make a significant contribution to changing the structure and physical and chemical properties of fluoride alloys of the tisonite type. X-ray phase analysis was used to identify the phase composition. New phases are installed. Microrentgenospectral analysis found that all the elements included in the LaF₃-SmF₃-GdF₃-ErF₃-ScF₃ system are distributed evenly over the surface. The use of predicted quasi-stable lattices based on chemical compounds in the AIRSS - GULP software package made it possible to fully describe the phase composition and quantitative characteristics of fluoride compounds. For the predicted structures, complete structural information is determined that allows modeling of diffractograms of reference lattices using standard methods. A comparison was made of model and experimental diffraction patterns. The proportion of phases and the criterion of divergence between experimental and theoretical intensities are determined. Using the AIRSS complex, a list of predicted quasi-stable phase lattices of known chemical composition was compiled. The crystallographic base of standards of double and triple phases of the tisonite type (LaF₃) for the studied fluoride system was used to determine the quantitative content of phases by the Rietveld method. Analysis of contributions to the integral intensity of individual phases of the LaF₃-SmF₃-GdF₃-ErF₃-ScF₃ fluoride system showed that with a high degree of divergence (R_wp = 7.56%), the main phases are F₁₅La₆, F₁₈Sm₆, F₁₂Sc₄La₄Sm₄Gd₄Er₄, the total share of which exceeds 0.96. The dominant phase is the F₁₈Sm₆ double phase. The quasi stable phase F₁₂Sc₄La₄Sm₄Gd₄Er₄ was predicted by the AIRSS complex.

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