Studies of phase transitions in order-disorder ferroelectrics. II. Calorimetric investigation of KD(2)PO(4)
Dyer, J. N.
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Calorimetric measurements on KD(2)PO(4) have been conducted, and the transition is found to be first order with an entropy change at T(c) of (0.2407+/- 0.0016)R. The entropy change associated with destruction of the polarization from O degrees K to T(c) is found to be (0.4234+/-0.0071)R. It is shown that a mean-field theory of the type proposed by Silbee, Uehling, and Schmidt can give a good account of the heat capacity and polarization to within 1 degree K of T(c), although the latent heat and entropy are not predicted satisfactorily, presumably because of the breakdown of the mean-field approximation close to the transition. Below T(c) the divergence in the heat capacity may be argued to be logarithmic in the region closer than 1 degree to T(c), or to be a 1/(T(c)-T)(1/2) in the region T(c)-2(o)<T<T(c)-0.2(o). Arguments are offered in favor of the logarithmic divergence.
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