On the theory of the structural phase transition in squaric acid
- 1 December 1976
- journal article
- research article
- Published by Wiley in Physica Status Solidi (b)
- Vol. 78 (2) , 721-727
- https://doi.org/10.1002/pssb.2220780233
Abstract
Crystals of the squaric acid C4H2O4(H2SQ) and C4D2O4(D2SQ) exhibit a structural phase transition at T0H = 370 K and T0D = 520 K. The phase transition is associated with the ordering of protons, moving above T0 in the symmetric double well potential of OHO bonds. The statistic of the phase transition in H2SQ and D2SQ is investigated in the cluster approximation with account of the tunneling of the protons. It is shown that the phase transition in the model is always of second order and that the increase of the ordering parameter with the decrease of temperature takes place in a large temperature range. The predictions of the theory are compared with experimental data at hand.Keywords
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