Mechanical Hardening of Nanostructured Ba_0.9R_0.1F_2.1 (R = Rare-Earth Elements) Crystals: Size Effect

Abstract—The effect of strong stoichiometry violations in the structural type of fluorite (CaF₂) on the microhardness of Ba_0.9R_0.1F_2.1 (R = rare-earth elements La–Lu) crystals is studied. The mechanical hardening of heterovalent solid solutions Ba_0.9R_0.1F_2.1 as compared to the BaF₂ matrix is due to the formation of nanosized clusters of point defects [Ba₈R₆F₆₉] substituting structural fragments [Ba₁₄F₆₄] (block-type isomorphism). The microhardness of nanostructured Ba_0.9R_0.1F_2.1 crystals is found to increase by 73% as the cluster size decreases from [Ba₈La₆F₆₉] to [Ba₈Lu₆F₆₉].