The current density-electric field intensity relationship of pre-heated potassium tetrachlorozincate (KZC) crystals (undoped and doped with Mn2+ in different concentrations) has been measured along the polar a-axis. The dependence was studied at selected temperatures covering the three high-temperature phases of KZC in order to investigate the type of conduction mechanism dominating in each phase. The original Richardson-Schottky (R-S) equation shows disagreement between calculated and experimental values of the Richardson and optical dielectric constants. The modified R-S equation fits the data well and facilitated the calculation of the barrier height, electronic mobility and high-frequency dielectric constant of KZC. The calculated parameters are in good agreement with the corresponding experimental values. The results indicated that the bulk- and electrode-limited mechanisms contribute to conduction in different phases of KZC. The temperature dependence of the dc conductivity along the polar axis of undoped and Mn2+-doped KZC shows anomalous behaviour in the region of the phase transitions. The dc conductivity and the activation energy of conduction (w) changed significantly due to doping. As indicated by the extremely high w values, superionic conduction is the dominating mechanism in the high-temperature part of the incommensurate (IC) and normal phases of KZC. Suppression of the superionic conduction by Mn2+-doping is observed. The effect of discommensurate pinning by Mn2+ ions and the possibility of dislocation formation on the dc conduction in the IC phase is also discussed

Lattice, rotation and intramolecular vibrations of ferrocene, Fe(C 5 H 5 ) 2 , crystallites of the factor group in the disordered phase are calculated using the correlation theorem based on group theory. The correlation between the species of the C 1 site symmetry occupied by cyclopentadienyl molecules and those of the factor group C 2 h of the crystal are calculated. The number of lattice vibrations of the cyclopentadienyl molecules is found to be 12, with active modes in Raman and infrared (IR) spectra. The same number of rotations for the cyclopentadienyl molecules is expected to be allowed in both spectra. The active number of intramolecular vibrations for the cyclo-pentadienyl molecules having D 5 molecular symmetry is expected to be 80 vibrations in both the Raman and the IR spectra. The effect of -irradiation with different doses and heat treatment at different temperatures on the IR spectra of ferrocene in the energy range 4000-200 cm -1 is discussed. A number of bands continuously shifted their position, and a decrease in intensity with increasing -dose is observed. New bands appeared in this spectral region for different annealing temperatures and different -doses. These changes are discussed in terms of intermolecular interactions between molecules within the unit cell.

Lattice, rotation and intramolecular vibrations of ferrocene, Fe(C 5 H 5 ) 2 , crystallites of the factor group in the disordered phase are calculated using the correlation theorem based on group theory. The correlation between the species of the C 1 site symmetry occupied by cyclopentadienyl molecules and those of the factor group C 2 h of the crystal are calculated. The number of lattice vibrations of the cyclopentadienyl molecules is found to be 12, with active modes in Raman and infrared (IR) spectra. The same number of rotations for the cyclopentadienyl molecules is expected to be allowed in both spectra. The active number of intramolecular vibrations for the cyclo-pentadienyl molecules having D 5 molecular symmetry is expected to be 80 vibrations in both the Raman and the IR spectra. The effect of -irradiation with different doses and heat treatment at different temperatures on the IR spectra of ferrocene in the energy range 4000-200 cm -1 is discussed. A number of bands continuously shifted their position, and a decrease in intensity with increasing -dose is observed. New bands appeared in this spectral region for different annealing temperatures and different -doses. These changes are discussed in terms of intermolecular interactions between molecules within the unit cell.

Ammonium zinc chloride (AZC) crystals doped with Mn2+ in different concentrations were grown from aqueous solutions at constant temperature. The dielectric constant (ε), dielectric loss (tan δ) and the ac conductivity (σac) along the polar axis were measured as functions of temperature and frequency. The temperature range covered the four high-temperature phases and the measuring frequency extended between 1-100 kHz. The measured properties facilitated the discussion of a model describing formation, annihilation and pinning of the discommensuration in crystal lattice and/or by structural imperfections. The effect of AZC decomposition in the normal phase and the possibility of protonic evolution on the ac conductivity were also considered. The presence of Mn2+ in the position of Zn2+ affected considerably the anomalies detected around the phase transition temperatures of ε, tan δ and σac. Conduction by translation and/or reorientation hopping are possible in two different frequency ranges depending on the crystal phase character.

*On leave of absence from Physics Department, Faculty of Science, Assiut University, 71516 Assiut, Egypt

Ammonium zinc chloride (AZC) crystals doped with Mn2+ in different concentrations were grown from aqueous solutions at constant temperature. The dielectric constant (ε), dielectric loss (tan δ) and the ac conductivity (σac) along the polar axis were measured as functions of temperature and frequency. The temperature range covered the four high-temperature phases and the measuring frequency extended between 1-100 kHz. The measured properties facilitated the discussion of a model describing formation, annihilation and pinning of the discommensuration in crystal lattice and/or by structural imperfections. The effect of AZC decomposition in the normal phase and the possibility of protonic evolution on the ac conductivity were also considered. The presence of Mn2+ in the position of Zn2+ affected considerably the anomalies detected around the phase transition temperatures of ε, tan δ and σac. Conduction by translation and/or reorientation hopping are possible in two different frequency ranges depending on the crystal phase character.

*On leave of absence from Physics Department, Faculty of Science, Assiut University, 71516 Assiut, Egypt

CuFe2−xAlxO4 (where x=0.0–0.6) have been synthesized at 950°C, 1000°C, 1050°C and 1100°C using the usual ceramic method. The Mössbauer measurements show reasonable values of magnetic as well as electric hyperfine interactions. At higher sintering temperatures, the spinel ferrite phase is partially dissociated forming delafossite phase in addition to the main matrix. The delafossite phase manifested itself as paramagnetic doublet overlapping the main Mössbauer spectra measured at room temperature. Furthermore, X-ray diffraction studies confirmed the presence of the CuFeO2 (delafossite) phase of Cu–Al ferrite

CuFe2−xAlxO4 (where x=0.0–0.6) have been synthesized at 950°C, 1000°C, 1050°C and 1100°C using the usual ceramic method. The Mössbauer measurements show reasonable values of magnetic as well as electric hyperfine interactions. At higher sintering temperatures, the spinel ferrite phase is partially dissociated forming delafossite phase in addition to the main matrix. The delafossite phase manifested itself as paramagnetic doublet overlapping the main Mössbauer spectra measured at room temperature. Furthermore, X-ray diffraction studies confirmed the presence of the CuFeO2 (delafossite) phase of Cu–Al ferrite

CuFe2−xAlxO4 (where x=0.0–0.6) have been synthesized at 950°C, 1000°C, 1050°C and 1100°C using the usual ceramic method. The Mössbauer measurements show reasonable values of magnetic as well as electric hyperfine interactions. At higher sintering temperatures, the spinel ferrite phase is partially dissociated forming delafossite phase in addition to the main matrix. The delafossite phase manifested itself as paramagnetic doublet overlapping the main Mössbauer spectra measured at room temperature. Furthermore, X-ray diffraction studies confirmed the presence of the CuFeO2 (delafossite) phase of Cu–Al ferrite

The dc conductivity of ammonium zinc chloride (AZC) crystal as functions of temperature, electric field intensity and Sr2+-doping concentration has been studied. Anomalous changes at the transition points connecting the antiferroelectric (AF), commensurate (C), incommensurate (IC) and normal (N) phases have been detected. The broadening of the peak anomaly at the C–IC phase transition suggested an important role for impurities assisting creation and annihilation of discommensuration (DC). Considerable shifts of the transition temperatures after doping with different Sr2+ concentrations were noticed. Electric conduction in AZC continuously increased with increasing Sr2+-concentration. Parameters extracted from the current density-electric field intensity relationship according to the usual Richardson–Schottky (R–S) emission equation were found inconsistent with corresponding experimental values. The results have been treated using the modified R–S equation for dielectrics with small electronic mean-free path. The Pool–Frenkel (P–F) conduction mechanism was also considered and the possibility of conduction by either of R–S or P–F was discussed.

The dc conductivity of ammonium zinc chloride (AZC) crystal as functions of temperature, electric field intensity and Sr2+-doping concentration has been studied. Anomalous changes at the transition points connecting the antiferroelectric (AF), commensurate (C), incommensurate (IC) and normal (N) phases have been detected. The broadening of the peak anomaly at the C–IC phase transition suggested an important role for impurities assisting creation and annihilation of discommensuration (DC). Considerable shifts of the transition temperatures after doping with different Sr2+ concentrations were noticed. Electric conduction in AZC continuously increased with increasing Sr2+-concentration. Parameters extracted from the current density-electric field intensity relationship according to the usual Richardson–Schottky (R–S) emission equation were found inconsistent with corresponding experimental values. The results have been treated using the modified R–S equation for dielectrics with small electronic mean-free path. The Pool–Frenkel (P–F) conduction mechanism was also considered and the possibility of conduction by either of R–S or P–F was discussed.