The effect of temperature on the sequence of the hardening precipitates in Al-1·1 wt-%Mg2Si balanced alloy has been investigated by means of differential scanning calorimetry, scanning electron microscopy and hardness measurements. The non-isothermal DSC thermograms exhibited seven reaction peaks. Out of these seven peaks, five are exothermic (representing precipitation) and two are endothermic (representing dissolution). The activation energy associated with the individual precipitates is calculated. The activation energy of nucleation of GP zones (54·3 kJ mol-1) is close to the migration energy of Si in Al (52·7 kJ mol-1). The activation energy associated with the precipitation of p" is determined as 77·6 kJ mol-1 and that for the formation of β' precipitates is 145·3 kJ mol-1. The latter value is close to that for Si diffusion in Al (124 kJ mol-1) and that of Mg diffusion in Al (131 kJ mol-1). It can be concluded that the precipitation of β' particles might be characterised by both the diffusion of Mg and Si atoms in Al to form β' precipitates

The effect of temperature on the sequence of the hardening precipitates in Al-1·1 wt-%Mg2Si balanced alloy has been investigated by means of differential scanning calorimetry, scanning electron microscopy and hardness measurements. The non-isothermal DSC thermograms exhibited seven reaction peaks. Out of these seven peaks, five are exothermic (representing precipitation) and two are endothermic (representing dissolution). The activation energy associated with the individual precipitates is calculated. The activation energy of nucleation of GP zones (54·3 kJ mol-1) is close to the migration energy of Si in Al (52·7 kJ mol-1). The activation energy associated with the precipitation of p" is determined as 77·6 kJ mol-1 and that for the formation of β' precipitates is 145·3 kJ mol-1. The latter value is close to that for Si diffusion in Al (124 kJ mol-1) and that of Mg diffusion in Al (131 kJ mol-1). It can be concluded that the precipitation of β' particles might be characterised by both the diffusion of Mg and Si atoms in Al to form β' precipitates

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

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

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

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 0.151.27. 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 0.151.27. 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