Considerable changes were observed in the X-ray diffraction pattern of ammonium zinc chloride after doping with Sr2+ in different concentrations and after irradiating with γ rays at different doses. The effect of γ-radiation and Sr2+ content on optical parameters of (NH4)2ZnCl4:x Sr2+ single crystals (x = 0.00, 0.020, 0.039, 0.087 or 0.144 wt.%) has been investigated. The transmittance near the absorption edge of unirradiated crystals and crystals irradiated with different γ-doses has been measured, hence the absorption coefficient (α) was calculated. The values of α at room temperature increased under the influence of γ-irradiation. The rate by which α increases with photon energy just before the absorption edge is strongly inhibited by higher γ-doses. The type of intraband transition in (NH4)2ZnCl4: x Sr2+ single crystals was found to be of the allowed indirect transition, and γ-irradiation had no effect on the type of transition. The values of the optical energy gap (Eg) were calculated as a function of γ-dose. The effect of γ-irradiation was found to be more pronounced on samples doped with x = 0.087 or 0.144 wt.% Sr2+. The results can be discussed on the basis of γ-irradiation-induced defects and Sr2+ concentration. A diagram representing probable transitions to the created bands due to irradiation could be constructed

The dielectric permittivity (∈) and dielectric losses (tan δ) of ferrocene crystallites are measured with different frequencies in the temperature range 140-375 K. The results confirm the existence of the phase transition at 163.9 K in addition to anomalous behaviour while heating indicating the presence of a metastable structure in the temperature range 250-290 K. The d.c. electrical conductivity (a) is measured in heating-cooling cycles between 120 and 300 K. The behaviour while cooling is completely different from that while heating and the phase transition becomes less pronounced in the second cooling-heating cycle. The σ-T relationship reveals an activation energy of conduction of 0.89 eV in the high temperature range while cooling. The effect of irradiating samples of ferrocene with γ-rays in different doses on both the dielectric permittivity and the electrical conductivity is also discussed. The current density (J) is measured as a function of the applied electric field (E) at three different temperatures; below the phase transition point, at room temperature and at 345 K in order to estimate the type of conduction dominates and the effect of E upon the conductivity measurements of this material. The effect of γ-irradiation with different doses on the J-E characteristics of ferrocene is also considered

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