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Specific heat calculated from the Raman frequency shifts close to the gimel-phase transition in NH4Br

We calculated the specific heat C-VI close to the lambda-phase transition in NH4Br on the basis of predictions of the Ising model. We have used our observed Raman frequencies of the nu(5) (134 cm(-1)) lattice mode to extract the critical exponent for the specific heat. The C-VI values calculated by us with this exponent value agree with the measured C-P data reported in the literature. This agreement is particularly good above T-lambda. This indicates that the observed behaviour of NH4Br can be satisfactorily explained close to the lambda-phase transition in this crystal.