A tin-119 Mössbauer study of the phase transitions in SnF2

Abstract

Tin-119 Mössbauer spectra have been recorded for the three known phases of SnF₂. In the monoclinic α phase the two structurally different tin environments have Mössbauer parameters which are indistinguishable from one another (δ= 3.40 mm s^–1, Δ= 1.52 mm s^–1): a small Goldanskii–Karyagin effect is observed. A discontinuity in the temperature dependences of the Mössbauer parameters occurs at the α→γ phase transition, ca. 425 K. The high-temperature γ phase has δ= 3.15 mm s^–1 and Δ= 1.95 mm s^–1, and exhibits a very large asymmetry in the intensities of the two lines of the quadrupole doublet. There is no such discontinuity at the γ⇌β second-order phase transition: progressive changes occur to give parameters for the β phase of δ= 3.11 mm s^–1 and Δ= 2.10 mm s^–1, and a slightly smaller line asymmetry.