Structural and spectroscopical study of a 2,5-diphenyl-1,3,4-oxadiazole polymorph under compression

The x-ray pattern and the Raman and luminescence spectra of crystalline 2,5-diphenyl-1,3,4-oxadiazole in one of its polymorphic forms (DPO II) have been investigated under pressure up to 5 GPa. The behaviour of the lattice parameters under compression was determined and it was found that the Murnaghan equation of state provides a good description of the volume-pressure relationship of DPO II. The values for the bulk modulus and its pressure derivative are K0 = 8.6 GPa and K'0 = 7.2. The analysis of the Raman spectrum under compression clearly shows the pressure-induced shift of the Raman modes to higher frequencies. The mode Grueneisen parameters for the lattice modes were determined. Additionally, it was found that the emission spectrum of DPO II moves to lower energies and that the luminescence intensity decreases when pressure is applied