The present work reports, for the first time, a direct experimental observation of the critical phenomenon associated with the B2–A2 order–disorder transition of Al–Fe binary alloys. Transmission electron microscopy and energy dispersion spectroscopy are employed to span the morphological changes through the transition line from the ordered B2 phase to the disordered A2 phase. Dark field images of the microstructure around the transition line for samples aged at 973 and 1073 K for various times show an interface roughening for the 100 antiphase domain boundaries in body-centered cubic binary alloys having the B2 structure. This observation confirms theory about the instability of the second-order transition in such alloys. This behaviour occurs for compositions with Al-content slightly higher (by 4 at.% Al) than that of the critical point of the equilibrium order–disorder transition. In addition, roughness-induced wetting transition is also observed for alloys having compositions ranging from 1.3 to 1.5 at.% Al above the transition line. The interface roughening transition is thought to be unstable second-order while the wetting transition is suggested to be a stable first-order one.

Ammonium zinc chloride (AZC) crystals doped with different strontium concentrations have been grown by the slow evaporation technique. Detailed temperature (300-450 K) and frequency (400-105 Hz) study of the dielectric constant (\varepsilon), loss factor (\tanδ) and the ac conductivity (σac) of the grown crystals has been carried out. Along the polar b-axis \varepsilon increased gradually with increasing temperature showing clear peaks at the phase transitions. Thermal recycling decreased \varepsilon, inhibited the peak height, decreased its broadening but without shifting the transition points. However, Sr2+-doping causes a shift of the transition temperature towards lower values and a decrease in the \varepsilon-peak broadening and height. Relation between 1/\varepsilon and T in the vicinity of the commensurate (C) to incommensurate (IC) phase transition revealed the validity of an equation similar to the Curie-Weiss law. Doping with Sr2+ in different concentrations causes a systematic change in the equation constants. Soliton pinning increased in the presence of Sr2+ leading to residual discommensurations (DC’s) in the C-phase. The dielectric constant decreased continually with increasing frequency for the undoped and Sr2+-doped samples. Doping with 0.144 wt% Sr2+ destroyed 25% of the C-phase, which means the possibility of having AZC crystal with reduced C-phase. σac increased with increasing frequency following a power law of the form σ=σo fs. Conduction by hopping was found to be dominant in all phases of AZC and after doping with Sr2+ in different concentrations. Mechanism for DC formation and annihilation was also discussed

Ammonium zinc chloride (AZC) crystals doped with different strontium concentrations have been grown by the slow evaporation technique. Detailed temperature (300-450 K) and frequency (400-105 Hz) study of the dielectric constant (\varepsilon), loss factor (\tanδ) and the ac conductivity (σac) of the grown crystals has been carried out. Along the polar b-axis \varepsilon increased gradually with increasing temperature showing clear peaks at the phase transitions. Thermal recycling decreased \varepsilon, inhibited the peak height, decreased its broadening but without shifting the transition points. However, Sr2+-doping causes a shift of the transition temperature towards lower values and a decrease in the \varepsilon-peak broadening and height. Relation between 1/\varepsilon and T in the vicinity of the commensurate (C) to incommensurate (IC) phase transition revealed the validity of an equation similar to the Curie-Weiss law. Doping with Sr2+ in different concentrations causes a systematic change in the equation constants. Soliton pinning increased in the presence of Sr2+ leading to residual discommensurations (DC’s) in the C-phase. The dielectric constant decreased continually with increasing frequency for the undoped and Sr2+-doped samples. Doping with 0.144 wt% Sr2+ destroyed 25% of the C-phase, which means the possibility of having AZC crystal with reduced C-phase. σac increased with increasing frequency following a power law of the form σ=σo fs. Conduction by hopping was found to be dominant in all phases of AZC and after doping with Sr2+ in different concentrations. Mechanism for DC formation and annihilation was also discussed

Undoped and Mn2+-doped with different concentrations of potassium zinc chloride (KZC) crystals were grown from aqueous solutions by slow evaporation. The dielectric constant (ε), dielectric losses (tan δ) and ac conductivity (σac) of the crystals in the ferroelectric-commensurate, incommensurate and normal phases have been measured as a function of frequency, in the range 1-100 kHz, and temperature, in the range 300-580 K. Virgin samples were subjected to measurements of the frequency dependence at selected temperatures and measurements of the temperature dependence was then followed using the same samples. The increase of ε with T could be due to a combination of conductivity, structural variations and discommensuration (DC) formation and pinning as well. The increase of tan δ with temperature was attributed to relaxation loss in addition to conduction loss, which increases more rapidly with temperature. The ac conductivity (σac) and tan δ along the polar axis of KZC increased significantly with increasing Mn2+ content while ε decreased. σac changed with frequency according to a power law of the form σac = f s where 0.15<s<1.27. A linear decrease of ε and tan δ with increasing the frequency was also found. The obtained results were treated by considering the effect of Mn2+-doping on stripples nucleation, DC evolution/annihilation, DC-lattice formation and DCs pinning by the crystal lattice and/or structural defects for virgin and thermally treated samples

Undoped and Mn2+-doped with different concentrations of potassium zinc chloride (KZC) crystals were grown from aqueous solutions by slow evaporation. The dielectric constant (ε), dielectric losses (tan δ) and ac conductivity (σac) of the crystals in the ferroelectric-commensurate, incommensurate and normal phases have been measured as a function of frequency, in the range 1-100 kHz, and temperature, in the range 300-580 K. Virgin samples were subjected to measurements of the frequency dependence at selected temperatures and measurements of the temperature dependence was then followed using the same samples. The increase of ε with T could be due to a combination of conductivity, structural variations and discommensuration (DC) formation and pinning as well. The increase of tan δ with temperature was attributed to relaxation loss in addition to conduction loss, which increases more rapidly with temperature. The ac conductivity (σac) and tan δ along the polar axis of KZC increased significantly with increasing Mn2+ content while ε decreased. σac changed with frequency according to a power law of the form σac = f s where 0.15<s<1.27. A linear decrease of ε and tan δ with increasing the frequency was also found. The obtained results were treated by considering the effect of Mn2+-doping on stripples nucleation, DC evolution/annihilation, DC-lattice formation and DCs pinning by the crystal lattice and/or structural defects for virgin and thermally treated samples

Undoped and Mn2+-doped with different concentrations of potassium zinc chloride (KZC) crystals were grown from aqueous solutions by slow evaporation. The dielectric constant (ε), dielectric losses (tan δ) and ac conductivity (σac) of the crystals in the ferroelectric-commensurate, incommensurate and normal phases have been measured as a function of frequency, in the range 1-100 kHz, and temperature, in the range 300-580 K. Virgin samples were subjected to measurements of the frequency dependence at selected temperatures and measurements of the temperature dependence was then followed using the same samples. The increase of ε with T could be due to a combination of conductivity, structural variations and discommensuration (DC) formation and pinning as well. The increase of tan δ with temperature was attributed to relaxation loss in addition to conduction loss, which increases more rapidly with temperature. The ac conductivity (σac) and tan δ along the polar axis of KZC increased significantly with increasing Mn2+ content while ε decreased. σac changed with frequency according to a power law of the form σac = f s where 0.15<s<1.27. A linear decrease of ε and tan δ with increasing the frequency was also found. The obtained results were treated by considering the effect of Mn2+-doping on stripples nucleation, DC evolution/annihilation, DC-lattice formation and DCs pinning by the crystal lattice and/or structural defects for virgin and thermally treated samples

Crystals of ammonium tetrachlorozincate (AZC) undoped and doped with Sr2+ or Mn2+ in different concentrations were grown by the slow evaporation method from an aqueous solution. The crystal morphology changed considerably by doping. The dopant concentration in the crystals was measured by the atomic absorption technique. Slight changes in the unit cell parameters of AZC after doping with Sr2+ or Mn2+ have been detected. Optical absorption measurements indicated strong influence of Sr2+ and Mn2+ doping. The optical energy gap at room temperature decreased continuously with increasing Sr2+ and Mn2+ concentration but with two different rates. The dc conductivity was also measured as a function of temperature for the undoped and two samples doped with 0.144 Sr2+ and 0.191 Mn2+ and the results were compared. Positions possibly occupied by Sr2+ and Mn2+ cations in AZC lattice have been identified

Crystals of ammonium tetrachlorozincate (AZC) undoped and doped with Sr2+ or Mn2+ in different concentrations were grown by the slow evaporation method from an aqueous solution. The crystal morphology changed considerably by doping. The dopant concentration in the crystals was measured by the atomic absorption technique. Slight changes in the unit cell parameters of AZC after doping with Sr2+ or Mn2+ have been detected. Optical absorption measurements indicated strong influence of Sr2+ and Mn2+ doping. The optical energy gap at room temperature decreased continuously with increasing Sr2+ and Mn2+ concentration but with two different rates. The dc conductivity was also measured as a function of temperature for the undoped and two samples doped with 0.144 Sr2+ and 0.191 Mn2+ and the results were compared. Positions possibly occupied by Sr2+ and Mn2+ cations in AZC lattice have been identified

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

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