Premium
Order‐Disorder Phase Transition in TEA+(TCNQ) 2 ‐
Author(s) -
Brau A.,
Farges J. P.,
Filhol A.,
Grassi H.
Publication year - 1983
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.2221200211
Subject(s) - differential scanning calorimetry , phase transition , phase (matter) , dispersion (optics) , debye , intramolecular force , heat capacity , diffraction , thermodynamics , chemistry , materials science , analytical chemistry (journal) , crystallography , stereochemistry , physics , organic chemistry , optics
The results of measurements of cell parameters by X‐ray diffraction and of differential scanning calorimetry, versus temperature, on TEA · TCNQ 2 are presented and compared to the σ 1 de conductivity behaviour. The differential scanning calorimetry measurements show a first order phase transition at 220 K attributed to the TEA disorder. From the thermal expansion a dispersion is observed of the cell parameter a for temperatures below 220 K, attributed to a certain amount of cation “ordering” at low temperatures. The variation of the cell parameter c (the direction of the TCNQ chains), versus temperature, permits the calculation of the contribution of the TCNQ columns to the total heat capacity of the TEA · TCNQ 2 by a simple linear model of coupled oscillators. It is found to be dominated by intramolecular vibrational TCNQ modes and by the cation movements. The chain axis component of the Debye temperature and of the Grüneisen coefficient are θ c ≈ 150 K and γ c ≈ 7.5.