15min:

H. YURTSEVEN, Department of Physics, Middle East Technical University, Ankara, 06531 - Turkey.

We establish here the modified Pippard relations by relating the specific heat C_p to the frequency shifts \frac1 \left( \frac\partial \partial T \right)_P and also the thermal expansivity _p to the \frac1 \left( \frac\partial \partial P \right)_T for the (140 cm^-1) Raman mode of NH₄Br close to its phase I- phase II transition. From our linear plots of C_p vs. \frac1 \left( \frac\partial \partial T \right)_P and _p vs. _p to the \frac1 \left( \frac\partial \partial P \right)_T , we extract the values of the slope DP/dT, which are close to the experimental value of 28.2 bar/^oC near the phase I-phase II transition in NH₄Br.