A new phase transition at about the room temperature and irregular thermal behaviour in the metastable state of γ-irradiated ferrocene

Abstract

We were able to detect the following two characteristic features of ferrocene. The first is a new irreversible phase transition at about the room temperature. The second is a metastable state between 250 and 290 K. To reach these two results the thermal expansion of γ-irradiated ferrocene samples is studied in cooling-heating cycles between the liquid nitrogen temperature and 375 K. The existence of the phase transition already known at ∼ 164 K is confirmed in addition to the detection of an irreversible sharp peak at ∼ 300 K. The differential scanning calorimetry (DSC) confirms the results of the thermal expansion. A clear, in some cases sharp, exothermic peak is observed in both nitrogen and helium ambient. The dielectric permittivity (ϵ) and dielectric losses (tan δ) of γ-irradiated ferrocene crystallites are also measured with different frequencies in the temperature range 140–375 K in cooling-heating cycles. The results confirm the existence of the phase transition at 163.9 K in addition to the newly detected one at 300 K. Moreover, DSC and dielectric permittivity experiments show anomalous changes upon heating representing a metastable state of ferrocene between 250 and 290 K. The effect of different γ-doses up to 106 Gy on the position and characteristics of the newly detected phase transition and the metastable state of ferrocene is also considered.