CALCULATION OF THE SPECIFIC HEAT FROM THE RAHAN FREQUENCY DATA FOR $NH_{4}Br$

Author Institution: Department of Physics, Istanbul Technical UniversityWe have calculated the specific heat $C_{y}$ for $NH_{4}Br$ near its $\lambda$-phase transition using our Raman frequency data of the $\nu_{5}LO_{r} $ ($177 cm^{-1}$) phonon mode of this crystal. For the $C_{v}$ calculation we have used an Ising model superimposed on an Einstein and/or Debye model. The specific heat $C_{VL}$ due to the lattice vibrations (Einstein model) and $C_{VI}$ due to the spin interactions (Ising model) were calculated according to $C_{V} = C_{VL} + C_{VI}$ at various temperatures using our observed Raman frequencies for the $177 cm^{-1}$ mode of $NH_{4}Br$. From our analysis it is concluded that an Ising model superimposed on an Einstein and/or Debye model explains adequately the observed behaviour in the lattice region of the $NH_{4}Br$ crystal