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.

Lattice, rotation and intermolecular vibrations of water molecules in the paraelectric phase of potassium ferrocyanide single crystals (KFCT) are calculated using the correlation theorem based on the group theory. The correlation between the site group symmetry C2 of the first type of the water molecules, H2O-I, and the factor group C2h of the crystal yield six fundamental lattice vibrations allowed in the infrared and Raman spectra. The same number for rotations are also expected to be allowed in both spectra. The active number of intermolecular vibrations in Raman and infrared spectra are the same as that for lattice vibrations. For the second type of the water molecules, H2O-II, existing in the C1 site, the total number of vibrations are 18 active modes in each spectrum. The FTIR spectrum of KFCT crystal measured at room temperature (in the paraelectric phase) in the energy range 4000-200 cm-1 gives exactly the same modes of vibrations as those expected theoretically. The effect of irradiating KFCT crystals with a dose of 5 x 105 Gy gamma radiation on the IR spectrum indicates changes in absorption bands.

Lattice, rotation and intermolecular vibrations of water molecules in the paraelectric phase of potassium ferrocyanide single crystals (KFCT) are calculated using the correlation theorem based on the group theory. The correlation between the site group symmetry C2 of the first type of the water molecules, H2O-I, and the factor group C2h of the crystal yield six fundamental lattice vibrations allowed in the infrared and Raman spectra. The same number for rotations are also expected to be allowed in both spectra. The active number of intermolecular vibrations in Raman and infrared spectra are the same as that for lattice vibrations. For the second type of the water molecules, H2O-II, existing in the C1 site, the total number of vibrations are 18 active modes in each spectrum. The FTIR spectrum of KFCT crystal measured at room temperature (in the paraelectric phase) in the energy range 4000-200 cm-1 gives exactly the same modes of vibrations as those expected theoretically. The effect of irradiating KFCT crystals with a dose of 5 x 105 Gy gamma radiation on the IR spectrum indicates changes in absorption bands.

The optical transmittance for potassium ferrocyanide (KFCT) single crystals were measured as a function of the wavelength at different temperatures in the range 275–320 K along the two axes (I 0 ) and (0 1 0) and hence the absorption coefficient (α) and optical band gap Eg were deduced. The type of transition was determined and the validity of Urbach's rule was checked. The steepness parameter (σ) and the exciton energy E0 were calculated at different temperatures. The temperature dependence of the energy gap was estimated and the result was confirmed through the calculation of dEg/dT from information about σ. The refractive index, the extinction coefficient and both the real and imaginary parts of the dielectric permittivity were also calculated as a function of photon energy and the results were discussed. The effect of doping KFCT with 2% of sodium nitroproced, cobalt sulphate or potassium dichromate on the same physical parameters was also discussed

The optical transmittance for potassium ferrocyanide (KFCT) single crystals were measured as a function of the wavelength at different temperatures in the range 275–320 K along the two axes (I 0 ) and (0 1 0) and hence the absorption coefficient (α) and optical band gap Eg were deduced. The type of transition was determined and the validity of Urbach's rule was checked. The steepness parameter (σ) and the exciton energy E0 were calculated at different temperatures. The temperature dependence of the energy gap was estimated and the result was confirmed through the calculation of dEg/dT from information about σ. The refractive index, the extinction coefficient and both the real and imaginary parts of the dielectric permittivity were also calculated as a function of photon energy and the results were discussed. The effect of doping KFCT with 2% of sodium nitroproced, cobalt sulphate or potassium dichromate on the same physical parameters was also discussed

Optical absorption measurements near the absorption edge have been studied in the energy range 3–5.5 eV on pure triglycine suphate (TGS) and TGS crystals doped with Cu2+, Mn2+ or Ni2+ in the temperature range 290–360 K. The temperature dependence of the band gap Eg(T) reveals an anomaly at the phase transition temperature for both pure and doped TGS crystals. Absorption coefficient data in the fundamental region are analysed and interpreted in terms of the allowed indirect transitions. The absorption edge following Urbach's rule exhibited exponential behaviour with temperature. Urbach parameters were calculated at different temperatures and the frequencies of effective phonons and electron–phonon interaction constants were determined for various phases

Optical absorption measurements near the absorption edge have been studied in the energy range 3–5.5 eV on pure triglycine suphate (TGS) and TGS crystals doped with Cu2+, Mn2+ or Ni2+ in the temperature range 290–360 K. The temperature dependence of the band gap Eg(T) reveals an anomaly at the phase transition temperature for both pure and doped TGS crystals. Absorption coefficient data in the fundamental region are analysed and interpreted in terms of the allowed indirect transitions. The absorption edge following Urbach's rule exhibited exponential behaviour with temperature. Urbach parameters were calculated at different temperatures and the frequencies of effective phonons and electron–phonon interaction constants were determined for various phases

The crystal structure of α- and β-LiIO3 at room temperature was examined using X-rays diffraction. Differential thermal analysis (DTA) with different heating rates (5–50 K/min) in the range 300–600 K was performed. The activation energy of phase transition was calculated by two methods based upon DTA. The d.c. electrical conductivity (σ) and dielectric permittivity () of α-LiIO3 crystals were measured along both the a- and c-axes in the temperature range 300–580 K. Anomaly in the σ–T relationship was observed at the α→γ phase transition. The dielectric permittivity increased abruptly at T0=520 K indicating strong structural changes at this temperature. The J–E characteristics along a- and c-axes were measured below and above T0 and hence the type of conduction was estimated. The optical transmittance (Tr) and reflectance (R) at room temperature were also measured in the wavelength range 190–900 nm and hence the absorption coefficient (α), refractive index (n), optical band gap (Egopt) and the type of transition were estimated. The anisotropic character of the measured properties of LiIO3 are discussed

The crystal structure of α- and β-LiIO3 at room temperature was examined using X-rays diffraction. Differential thermal analysis (DTA) with different heating rates (5–50 K/min) in the range 300–600 K was performed. The activation energy of phase transition was calculated by two methods based upon DTA. The d.c. electrical conductivity (σ) and dielectric permittivity () of α-LiIO3 crystals were measured along both the a- and c-axes in the temperature range 300–580 K. Anomaly in the σ–T relationship was observed at the α→γ phase transition. The dielectric permittivity increased abruptly at T0=520 K indicating strong structural changes at this temperature. The J–E characteristics along a- and c-axes were measured below and above T0 and hence the type of conduction was estimated. The optical transmittance (Tr) and reflectance (R) at room temperature were also measured in the wavelength range 190–900 nm and hence the absorption coefficient (α), refractive index (n), optical band gap (Egopt) and the type of transition were estimated. The anisotropic character of the measured properties of LiIO3 are discussed

The dielectric permittivity (ε) and the dc electrical resistivity(ρ)of pure LiNH4SO4 (LAS) single crystals have been measured in the temperature range 230-350 K including the lower phase transition at about 283 K. Anomalous behaviours before and at the transition point were observed. The temperature dependence of ρ yielded AE = 0.11 and 0.91 eV for the energy activating the charge transport mechanisms before and after the transition. A pre-transition phenomena was observed while measuring both ρ and ε. The optical transmittance at different temperatures was also measured and hence the absorption coefficient (α) and optical band gap Eopt,g were deduced. The validity of Urbach's rule was checked and hence the steepness parameter σ and the exciton energy E0 were calculated at different temperatures. ρ, ε, α and Eopt,g for LAS crystals doped with 5% Co2+ or Cu2+ were also measured and they were compared with the results of the pure crystals