Synthesis of Nonstoichiometric Samarium Fluoride SmF2 + x

Abstract

The products of interaction of SmF₃ with metallic Sm⁰, Si, and molecular hydrogen in quartz, graphite, and molybdenum containers have been investigated by X-ray diffraction. It is shown that reduction occurs with the formation of nonstoichiometric cubic SmF_{2 + x} (sp. gr. Fm3̅m, unit-cell parameter a = 5.8517(2) Å) with a content x = 0.108 only in the case of synthesis of SmF₃ with metallic Sm⁰ in a quartz ampoule. The transformation of the SmF_{2 + x} phase composition in air at room temperature has been studied for the first time. It is found that SmF_2.108 passes into the superstructural phase Sm₁₃F_32–δ (sp. gr. R3̅) with the unit-cell parameters a = 14.7354(4) Å and c = 10.1156(4) Å for 60 days. The use of Sm⁰, Si, and H₂ as reducing agents for SmF₃ is inefficient because of the weak tendency of the latter to reduction: the process occurs also with a low yield of the Sm₁₃F_32–δ phase and of the α-SmF₃-based phase as impurity in the case of direct reduction by hydrogen.