Study of the influence of pressure on the p-terphenyl phase transition by Raman scattering

The influence of pressure on the p-terphenyl phase transition is analysed by Raman Scattering. This study improves the understanding of the mechanism of this structural instability which is related to competing intramolecular and intermolecular forces. So, as expected, the phase diagram shows that the transition temperature decreases with increasing pressure. The observation of a soft mode, at high pressure in the low temperature phase, showing a change-over from an order-disorder regime to a displacive one, also agrees with the transition mechanism. Furthermore, our study indicates that the transition becomes clearly discontinuous at high pressure.