Spectroscopic modifications of the Pippard relations for NaNO2 in the sinusoidal antiferroelectric phase

We establish in this study a linear variation of the specific heat Cp with the frequency shifts (l/v)(delta v/delta T) in the sinusoidal antiferroelectric phase of NaNO2, according to the first Pippard relation which we have modified spectroscopically. For this linear relationship we use the Brillouin frequencies of acoustic phonon modes for the q[010], q[001] and q[100] modes of NaNO2 in the sinusoidal antiferroelectric phase. We then calculate dT/dP values due to those modes studied for NaNO2, which agree with the literature values.