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.

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.