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Analysis of the Specific Heat for the Transitions of the Phases I-II-III-IV in (N(CH3)(4))(2)CUCl4 Crystal

The temperature dependence of the specific heat C-p is analyzed here using the experimental data according to a power-law formula with the critical exponent a for the transitions of commensurate (I), incommensurate (II) and the ferroelastic (III and IV) phases in (N(CH3)(4))(2)CUCl4 crystal. From our analysis, we extract the value of a approximate to 0 above and below T-c for the successive phase transitions of which is expected from the mean field theory (alpha =0 discontinuity), XY model (alpha =0 log) and the two dimensional Ising model (alpha =0 log). This indicates that the transitions between commensurate and incommensurate phases and also between incommensurate and ferroelastic (III) phases in TMATC-Cu are of a second order type.