The specific heat of N(CH3)(4)MnBr3 by adiabatic calorimetry

The specific heat of N(CH3)(4)MnBr3 has been measured by adiabatic calorime try, using both static and dynamic methods. The obtained results have permi tted the calorimetric characterization of the phase transition which the cr ystal shows at 143 K. The comparison with other compounds of the family has been used to generate an adequate baseline for the normal lattice contribu tion to the specific heat. These results allow for an accurate estimation o f the phase transition thermodynamic functions: Delta H = 218 R K and Delta S = 1.58 R. The calorimetric data are very close to those found for the is omorphous N(CH3)(4)CdBr3 and suggest a similar frequency spectrum for the l attice vibrational modes and the anharmonic contributions to the specific h eat.