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Thermodynamics of the Phase Transition Sequence in the Incommensurate Compound (N(CH 3 ) 4 ) 2 CuBr 4
Author(s) -
LópezEcharri A.,
RuizLarrea I.,
Tello M. J.
Publication year - 1989
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.2221540113
Subject(s) - phase diagram , thermodynamics , tetramethylammonium , phase transition , calorimetry , ferroelectricity , adiabatic process , phase (matter) , chemistry , atmospheric temperature range , phenomenological model , crystallography , materials science , condensed matter physics , physics , organic chemistry , ion , dielectric , optoelectronics
The prototype‐incommensurate‐ferroelectric‐ferroelastic phase transition sequence in (N(CH 3 ) 4 ) 2 CuBr 4 is studied by adiabatic calorimetry in the temperature range 60 to 343 K. The thermodynamic function values assigned to the successive phase transformations permit a comparative study with other tetramethylammonium tetrahalogenmetallates. The enthalpies involved in their phase transition sequences can be related to the packing of the crystal unit cell and to the position of each compound in a common pressure‐temperature phase diagram. In the case of (N(CH 3 ) 4 ) 2 ‥CuBr 4 , this diagram is correctly described by a simple phenomenological model. A brief discussion on the critical exponents associated to the specific heat (α = α′ = 0.01 for ‖ T − T 0 ‖ < 0.2 K) and to the order parameter, for the prototype‐incommensurate phase transition, is also included.