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Journal of Physical Studies 2(4), 524–535 (1998)
DOI: https://doi.org/10.30970/jps.02.524
THE MEAN-FIELD ANALYSIS OF
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M. M. Khoma, A. A. Molnar, Yu. M. Vysochanskii
Institute of Solid State Physics and Chemistry, Uzhgorod University,
46 Pidhirna Str., Uzhgorod, UA–294000, Ukraine
In the mean–field approximation, assuming the linear concentration dependence of the thermodynamic potential coefficients and taking into account the higher harmonics of spatial order parameter modulation in the incommensurate phase and interaction between order parameter and elastic deformation, the temperature and concentrational dependencies of the principal thermodynamical characteristics of Sn$_{2}$P$_{2}$(Se$_{x}$S$_{1-x} $)$_{6}$ uniaxial ferroelectrics are calculated and compared with the experimental data. Some discrepancy exists at the quantitative comparison of calculated and experimental data for the temperature dependencies of heat capacity, amplitude and wave vector of modulation, essentially in the vicinity of the lock–in phase transition in incommensurate phase.