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.

Optical transmission and reflection measurements for crystals of potassium tetrachlorozincate (KZC) doped with Mn2+ or Ni2+ in different concentrations and irradiated with different γ-doses have been carried out along the three crystallographic axes. The results were analyzed to determine the absorption coefficient (), type of optical transition and the optical energy gap (Eg). Different absorption bands along the three axes have been observed. Doping with Mn2+ or Ni2+ affected the intensity and position of these bands. Irradiation by γ either created or inhibited some of these bands. The nature of the transition involved was found to be the indirect allowed one. Doping with Mn2+ or Ni2+ up to 0.41 wt% and irradiating with γ-doses up to 150 kGy did not change the type of transition. The optical energy gap decreased considerably after doping and irradiating KZC

Optical transmission and reflection measurements for crystals of potassium tetrachlorozincate (KZC) doped with Mn2+ or Ni2+ in different concentrations and irradiated with different γ-doses have been carried out along the three crystallographic axes. The results were analyzed to determine the absorption coefficient (), type of optical transition and the optical energy gap (Eg). Different absorption bands along the three axes have been observed. Doping with Mn2+ or Ni2+ affected the intensity and position of these bands. Irradiation by γ either created or inhibited some of these bands. The nature of the transition involved was found to be the indirect allowed one. Doping with Mn2+ or Ni2+ up to 0.41 wt% and irradiating with γ-doses up to 150 kGy did not change the type of transition. The optical energy gap decreased considerably after doping and irradiating KZC

The dielectric constant, , and the d.c. conductivity, σ, were measured along the a-, b- and c-axes of (NH4)2ZnCl4 (AZC) crystal in the 300–450 K temperature range. Crystals of AZC grown from aqueous solutions containing excess of ZnCl2 were used. The value of the dielectric permittivity of AZC is extremely small compared to other ferroelectric crystals. Pronounced broad or step-like peaks at the phase transition temperatures were detected along the a- and b-axes, while along the c-axis is temperature independent up to the end of the measuring range. Reciprocal of the dielectric permittivity in the range of the commensurate to incommensurate phase transition obeys a relation similar to the Curie–Weiss law that is valid for second order ferroelectric/paraelectric phase transitions. The constants of the proposed relationship applied to the cooling run are given. The J–E characteristics along the three crystallographic axes were measured in the normal, incommensurate, commensurate and antiferroelectric phases. Hence, the type of conduction mechanism has been estimated. Parameters of Poole–Frenkel and Richardson–Schottky types of conduction mechanism have been determined. The effect of applied electric field on the conductivity measurement was also tested. Conductivity anomalies with different character were observed at the phase transition temperatures. The ln σ−1000/T dependence revealed thermal activation energy of conduction along the a-, b- and c-axes with different values in different phases of AZC.

The dielectric constant, , and the d.c. conductivity, σ, were measured along the a-, b- and c-axes of (NH4)2ZnCl4 (AZC) crystal in the 300–450 K temperature range. Crystals of AZC grown from aqueous solutions containing excess of ZnCl2 were used. The value of the dielectric permittivity of AZC is extremely small compared to other ferroelectric crystals. Pronounced broad or step-like peaks at the phase transition temperatures were detected along the a- and b-axes, while along the c-axis is temperature independent up to the end of the measuring range. Reciprocal of the dielectric permittivity in the range of the commensurate to incommensurate phase transition obeys a relation similar to the Curie–Weiss law that is valid for second order ferroelectric/paraelectric phase transitions. The constants of the proposed relationship applied to the cooling run are given. The J–E characteristics along the three crystallographic axes were measured in the normal, incommensurate, commensurate and antiferroelectric phases. Hence, the type of conduction mechanism has been estimated. Parameters of Poole–Frenkel and Richardson–Schottky types of conduction mechanism have been determined. The effect of applied electric field on the conductivity measurement was also tested. Conductivity anomalies with different character were observed at the phase transition temperatures. The ln σ−1000/T dependence revealed thermal activation energy of conduction along the a-, b- and c-axes with different values in different phases of AZC.

The thermal decomposition behaviour of unirradiated and pre-γ-irradiated piperacillin (pipril) as a semi-synthetic penicillin antibiotic has been studied in the temperature range of (273-1072 K). The decomposition was found to proceed through three major steps both for unirradiated and γ-irradiated samples. Neither appearance nor disappearance of new bands in the IR spectrum of piperacillin was recorded as a result of γ-irradiation but only a decrease in the intensity of most bands was observed. A degradation mechanism was suggested to explain the bond rupture and the decrease in the intensities of IR bands of γ-irradiated piperacillin

The thermal decomposition behaviour of unirradiated and pre-γ-irradiated piperacillin (pipril) as a semi-synthetic penicillin antibiotic has been studied in the temperature range of (273-1072 K). The decomposition was found to proceed through three major steps both for unirradiated and γ-irradiated samples. Neither appearance nor disappearance of new bands in the IR spectrum of piperacillin was recorded as a result of γ-irradiation but only a decrease in the intensity of most bands was observed. A degradation mechanism was suggested to explain the bond rupture and the decrease in the intensities of IR bands of γ-irradiated piperacillin

Optical absorption along the three crystallographic axes of (NH4)2ZnCl4 single crystals is reported over a temperature range from 276 K to 350 K. Our results clearly confirm the antiferroelectric to commensurate phase transition at 319 K. Analysis reveals that at the absorption edge the type of transition is the indirect allowed one. The indirect band gaps at various temperatures are determined and their temperature dependence is estimated in the antiferroelectric and commensurate phases. Optical parameters related to the temperature dependence of the energy gap are evaluated. The single-effective oscillator model was used to describe the imaginary part of the dielectric constant, which facilitate calculation of the dipole moment parameters. The steepness parameter is given, its value is used to estimate the temperature dependence of the indirect energy gap and the result is compared with that calculated graphically. In the region of the absorption edge, the absorption coefficient obeys Urbach's rule. Urbach characteristic parameters are determined and their temperature dependence is investigated. Correlation between different parameters is considered. Most of the results confirm the optical isotropic nature of AZC crystals. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)