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On the theory of the structural phase transition in squaric acid
Author(s) -
Zinenko V. I.
Publication year - 1976
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2220780233
Subject(s) - squaric acid , phase transition , phase (matter) , order (exchange) , atmospheric temperature range , quantum tunnelling , crystallography , cluster (spacecraft) , condensed matter physics , chemistry , physics , thermodynamics , quantum mechanics , organic chemistry , finance , computer science , economics , programming language
Crystals of the squaric acid C 4 H 2 O 4 (H 2 SQ) and C 4 D 2 O 4 (D 2 SQ) exhibit a structural phase transition at T 0H = 370 K and T 0D = 520 K. The phase transition is associated with the ordering of protons, moving above T 0 in the symmetric double well potential of OHO bonds. The statistic of the phase transition in H 2 SQ and D 2 SQ 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.