Infrared study for the phase transition of re-heated diphenyl carbazide C13H14N4O

The temperature dependence of IR spectra of re-heated diphenyl carbazide C13H14N4O have been investigated under normal pressure. The data is reported here between room temperature and up to the melting point (similar to 160 degrees C) of diphenyl carbazide (DPC) and the IR spectra are recorded up to 4000 cm(-1). This study is an extension of a recent one, which detected the presence of a phase transition by DTA and DSC at similar to 90 degrees C. It includes measurements and interpretations of the IR spectral band shape, frequencies of modes and absorbance as a function of temperature. Special attention is paid to the most sensitive mode which reflects the phase transformation process in detail. These modes are 3055 cm(-1), 1658 cm(-1), 1567 cm(-1) and 1308 cm(-1) in which the variations confirm the gradual phase transition due to the growing of the disordering state in the crystals. The data obtained by IR spectroscopic analysis strongly indicates the presence of three different phase states for DPC organic compound, The first is the room temperature phase (orthorhombic), the second is that obtained after melting and even at room temperature (amorphous), and finally the third is that obtained by reheating as the temperature exceeds 90 degrees C (high temperature phase). These structural changes are checked by X-rays and the high temperature phase is found to be triclinic with a = 4.5077 Angstrom, b = 4.9010 Angstrom and c = 24.0637 Angstrom. (C) 1997 Elsevier Science B.V.