Mössbauer Effect and Raman Studies of the Structural Phase Transitions in K2[SnCl6]

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Abstract
The 110Sn Mössbauer spectrum and the Raman phonons in polycrystalline samples of K2[SnCl5] have been investigated in the temperature range from 4 and 150 K, respectively, to 300 K. With decreasing temperature a discontinuous increase of the halfwidth of the Sn‐Mössbauer line and a concommitant change in the isomeric shift are observed. The former is attributed to the appearance of a quadrupole splitting at the first order crystallographic transition at T1 = 262 K. The Raman spectrum of the low‐symmetry phase exhibits an external lattice mode located at 33 cm−1 at 150 K. It shows a pronounced softening following the relation ω(T) ∼ (T0 − T)1/2 where T0 is close to T1. Two models are discussed in which alternatively a zone centre and a zone boundary rotary mode is considered to drive the crystallographic transition.