D. Baltrunas et al., Temperature investigations of the ferroelectric crystals Sn2P2S6 and Sn2P2Se6 by means of Sn-119 Mossbauer spectroscopy, J PHYS-COND, 11(14), 1999, pp. 2983-2992
Mossbauer spectra of Sn2P2S6 and Sn2P2Se6 proper uniaxial ferroelectrics we
re investigated over a wide temperature region including phase transition p
oints with the aim of studying the dynamics of ferroactive tin ions used as
a Mossbauer isotope (Sn-119). The characteristics of the gamma-resonance l
ines (isomer shift, effect probability, etc) and the parameters calculated
from the measured spectra in the Debye approximation (mean square displacem
ent, Debye-Waller factor, Debye temperature, etc) were analysed in comparis
on with the available structural and thermodynamical data. The data obtaine
d support the assumption of a two-well local potential of the tin atoms in
addition to the displacement of their time-averaged position below the phas
e transition points. It was concluded that displacement and ordering occur
in the same Sn sublattice, and that the variation in long-range forces lead
s to lattice instability.