M.A. Ahmed

Rare earth doping effect on the structural and electrical properties of Mg-Ti ferrite

The electrical properties, shrinkage, porosity and X-ray diffraction analysis for Mg-Ti ferrite of the general formula Mg 1+ xTixRyFe2 � 2xyO4; x=0.5, y=0, 0.025 and R=(Nd, Gd and La) were studied. The investigated samples were crystallized in the spinel phase. The measurements of the electrical properties were carried out at different temperatures (295- 750 K) as a function of the applied frequency (50-1000 kHz). The experimental results show that the rare earth ions initiate new sites called dodecahedral (C-sites) and at the same time increase the valence exchange between the different metal ions existing in the different sites. This behavior takes place at certain concentrations of the rare earth ions. The low rare earth concentration as well as the high sintering times (100 h) leads to an inflection in the electrical properties. Verwey conduction mechanism and hopping are used to interpret the conductivity of the samples. D 2003 Elsevier Science B.V. All rights reserved.

Influence of yttrium ions on the magnetic properties of Ni–Zn ferrites

Abstract The ferrites having the general formula Ni1−xZnxFe2O4 with 0⩽x⩽0.5 and Ni0.5Zn0.5YyFe2−yO4 with 0.02⩽x⩽0.10 were synthesized under atmospheric pressure, and showed single spinel phase in X-ray diffractogram patterns. The structural properties and the magnetic behavior at different magnetic fields and concentration of the substituted nonmagnetic (Zn2+) and yttrium (Y3+) ions were studied. The magnetic constants have been calculated from DC magnetic susceptibility measurements. The transition from ferrimagnetic to the paramagnetic state is accompanied by an increase in the thermo-emf. It was observed that the magnetic moment of the system and the Curie temperature decreased by substitution of Zn. This means that some cations on the B site migrate to the A site which control the physical properties of the system.

Effect of dopant concentration on the electrical properties of polyvinyl alcohol (PVA)

The real part of the dielectric constant (ε′) of pure and doped polyvinyl alcohol (PVA) with 1, 2 and 3 wt% vanadate was measured as a function of temperature and frequency. (ε′) decreases with increasing frequency due to a rapid variation of the field accompanied with the applied frequency as well as the disordering of the segmental parts of the polymer chain. The vanadate effects appear in a form of increasing the crystallinity in the sample leading to a decrease in (ε′), except in the case of 2 wt% vanadate in which (ε′) is drastically increased. The d.c. conductivity for the vanadate doped PVA is measured as a function of temperature. The values of the activation energy as obtained from the experimental data give information about the presence of more than one conduction mechanism as well as the useful applications of PVA, especially in the field of electronics.

Electrical conductivity of the compounds (CH2)n(NH3)2FeCl4−xBrx (n = 8,9 and 10, x = 0,1 and 2)

Abstract The electrical conductivity of the compounds (CH 2 ) n (NH 3 ) 2 FeCl 4− x Br x ( n = 8, 9 and 10 and ( x = 0, 1 and 2) was measured in the temperature range from liquid nitrogen up to near the melting point of the samples. The effects of a gradual replacement of Cl − ions by Br − ions as well as the effect of layer spacing on the electrical conductivity are discussed. The phase transition points are determined and the values of the activation energies for the low (phase I) and high (phase II) temperature phases are calculated and listed.

Effect of Ti4+ ions on the magnetic and dielectric properties of Mg-ferrite

Abstract X-ray diffraction, the real part ( e ′), the imaginary part ( e″ ) of dielectric constant, and the molar magnetic susceptibility ( χ M ) for Mg 1+ x Ti x Fe 2−2 x O 4 ferrite (0.1⩽ x ⩽0.9) were studied. The date of X-ray diffraction showed that the unit cell parameter increases with Ti concentration and ascribed to the predicted variation of the cation distribution, while Mg 2+ ions are highly diffusible and very sensitive to heat. The effect of dilution by Ti ions is discussed in terms of increasing superparamagnetic and single domain (SP/SD) grains. The measurements of e′ were performed at different temperatures as a function of frequency, while the magnetic susceptibility was studied at different magnetic field intensities. The variation of the dielectric properties depends mainly on the valence exchange between the different metal ions in the same site or in different sites. All parameters such as e′ , e″ , χ M showed a decrease in value with increasing Ti and Mg concentration. The dispersion in e′ with frequency disappeared gradually with increasing Ti concentration.

Conductivity improvement of Li-Co-Yb ferrite

The effect of γ-irradiation on some physical properties of rare earth ferrite of the general formula Li0.5 + zCozYbxFe2.5-2z-xO4, (z = 0.1, x = 0.00, 0.025, 0.050,...,0.200) was discussed. The temperature dependence of the polarization and resistance was studied in the range (300 K≤T≤700 K) at different frequencies (10 kHz≤f≤1 MHz). The relaxation time and the activation energy were calculated for γ doses of 1 and 3 Mrad. Also, a comparison was made between the ac resistance, before and after irradiation, for the samples with different Yb concentrations (0.0≤x≤0.2). The results after irradiation with a 1 Mrad dose of γ-rays showed that the resistance at the critical concentration decreases from 800 to 25 kΩ, at room temperature. Furthermore, with increasing temperature the resistance ranged from R≈130 kΩ at T≈310 K to R≈0.13 kΩ at T≈640 K. Thus, it is possible to improve the conductivity of this type of rare earth ferrite material to be used in technological applications at room temperature as well as at high temperatures.

Dependence of dielectric behaviour of Mn-Zn ferrite on sintering temperature

The dielectric constant of Mn-Zn ferrite was measured at different temperature and frequencies as a function of sintering temperature ranging from 1200°C to 1400°C at heating rate of 6°C/min. The resistivities as well as Seebeck coefficient were measured in the same range of temperature. More than one type of polarization is expected to vary the dielectric constant. Hoping mechanism was the predominant one in conduction processes. The grain size was calculated from X-rays and SE micrographs and it was found to decrease with increasing sintering temperature.

Electrical resistivity of ferrites of the general formula Mg1+t Fe2-2t Ti t O4 (t=0.1,0.3,0.4,0.5)

The electrical resistivity of the ferrites Mg1+tFe2-2tTitO4 (t=0.1, 0.3, 0.4, 0.5) has been measured in the temperature range of 30 to 300° C. A break in Inϱ against 1/T aroundTC has been observed. This break is associated with a change in the activation energy around the Curie temperature. The conductivity behaviour is discussed in terms of the cation distribution in these ferrites.

Comparative synthesis and antimicrobial action of silver nanoparticles and silver nitrate

The high wave of antibiotic bacterial resistance has addressed an importance for administration of different antibacterial agents, as silver nanoparticles (Ag NPs). However, many investigators still suffer conflict in the mechanistic antimicrobial action of Ag NPs and Ag+ ions. In this regard, our study investigated the comparative antimicrobial action of different sizes of Ag NPs as 8 (nAg1) and 29 (nAg2) nm, in comparison with silver nitrate (AgNO3) against five different bacterial species; Aeromonas hydrophila (A. hydrophila), Pseudomonas putida (Ps. putida), Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Bacillus subtilis (B. subtilis) using agar diffusion assay and minimum inhibitory concentration (MIC). The key role of the size of nanomaterials was detected, as the smaller Ag NPs (nAg1) showed more antimicrobial action than the larger particles. Transmission electron microscopy (TEM) studies demonstrated the different mechanistic antibacterial actions of Ag NPs and AgNO3. The effect of combining Ag NPs with antibiotics was also investigated. Synergistic effect of combining Ag NPs with ampicillin was detected against S. aureus, in a size-dependent manner as well. To summarize, our results point towards the major role played by the size of Ag NPs in their antimicrobial effects and the different toxic mechanisms of actions induced by Ag NPs and AgNO3.

Electrical conduction in ?-irradiated and unirradiated Fe3O4, CdFe2O4 and Co x ZN1?x Fe2O4 (0 ?x ? 1) ferrites

The electrical conductivity of γ-irradiated and unirradiated finely divided ferrites of composition Fe3O4, CdFe2O4 and Cox Fn1−xFe2O4(0 ≤x ≤ 1) was studied in a nitrogen atmosphere as a function of temperature. Fe3O4, ZnFe2O4 and CdFe2O4 showed n-type conduction, whereas CoFe2O4 showed p-type conduction. For CoxZn1-xFe2O4 it was found that the type of conduction varies with the composition of ferrites. The electrical conduction in Fe3O4, and CoxZn1−xFe2O4(0 ⩽x ≤ 1) was explained by a hopping mechanism, whereas the conduction in ZnFe2O4 and in CdFe2O4 is interpreted on the basis of the transfer of charge carriers through cation vacancies present on octahedral sites. The effect of γ-irradiation on the conductivity, activation energy, charge carriers and the conduction mechanism is discussed.