Exothermic phase transition in re-heated diphenyl carbazid C13H14N4O

Abstract The effect of heating and re-heating on diphenyl carbazid (DPC) organic compound is studied between room temperature and its melting point ~162 °C by a set of DTA and DSC measurements. Also, electrical measurements (including d.c. resistance, dielectric constant and pyroelectric current) are carried out in order to confirm the results of thermal analysis. Various results obtained indicate, for the first time, that diphenyl carbazid undergoes a previously unknown exothermic phase transition in the vicinity of 90 °C during re-heating, i.e. there are two different phases I and II, where: DPC(II) → 90 °C → DPC(I). The heat required for this transition is calculated and found to be 39 J/gm. This phase transition is correlated with the onset of the hydrogen bonding of the amino ions (N-H). The electrical conduction is found to be activated by energies of 0.8 eV and 0.5 eV for the phases I and II, respectively. An energy model is also suggested to account for the conduction mechanism in the revealed phase of the re-heated DPC compound.