Breakdown of the Landau Theory in the Ferroelectric Phase Transition of Dicalcium Strontium Propionate

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Abstract
Measurements of the thermal expansion coefficient β3, the dielectric constant ε33, and the spontaneous polarization Ps are made for annealed Ca2Sr(C2H5CO2)6 near the Curie point. Systematic deviations from mean-field theory are observed. The critical indices are determined to be γ=1.33±0.10 for ε33 in the range 0.5°C<T−Tc<9°C, β=0.31±0.03 for Ps in the range 0.5°C<Tc−T<5°C, and α=0 (logarithmic singularity) for β3 in the range 0.4°C<T−Tc<3°C.