Phase transitions in hydrogen-bonded phenol–amine adducts: analysis by ferroelastic theory

Mean field statistical mechanics of model Hamiltonian for hydrogen bonded phase transitions

“…(b) A mean field type of calculation of the thermodynamic behaviour using a variational method is able to explain the main features of the phase transition, in agreement with a Landau theory of ferroelastic phase transitions [5]. The essential physical mechanism proposed in the microscopic theory is that the interactions of the hydrogen bonds with phonons induce indirect long-range interactions between the hydrogen bonds.…”

Microscopic theory of phase transitions in hydrogen-bonded phenol-amine adducts

“…The critical exponent for the transition is 1 / 2, in agreement with the prediction made by a phenomenological Landau free energy expansion. 16 A broken symmetry is associated with this transition-as the axis tilted away, the mirror symmetry is necessarily broken.…”

“…This discontinuity in meanfield heat capacity is a common feature of all second order phase transitions, and is in agreement with the earlier Landau theory prediction. 16 The specific heat jump in the bulk crystal is then given by…”

“…16 Here each ␥ i and C are constants independent from u i and ͑T − T c ͒. Minimizing this approximated free energy with respect to each u i near the critical point, to leading order we get:…”

Temperature-dependent isomorphous phase transition studies in molecular crystals of 2,4,4′-trimethoxybenzophenone

“…With the changing of the temperature, the compound (I) undergoes a first-order displacive reversible isomorphous phase transitions. Our previous studies [2][3][4][5] of second order phase transitions are ferroelastic in nature and have theoretically been described macroscopically by Landau ferroelastic theory [3] and microscopically using the pseudo-spin approach [4]. We also have a case of first-order reversible isomorphous phase transition which has been demonstrated macroscopically by Landau theory [6].…”