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1

AC Electrical Conductivity and Dielectric Properties of Perovskite (Pb,Ca)TiO_3 Ceramic

100%

El-Mallah H.

Acta Physica Polonica A

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2012

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vol. 122

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issue 1

174-179

EN

Pb_{1 - x }Ca_{x}TiO_3 perovskite crystalline structure with x = 0, 0.2, 0.6, 0.7, and 0.8 were prepared by mixture method. The ac conductivity and dielectric properties of the studied bulk compositions have been investigated in the frequency range 1 × 10^3 - 5 × 10^6 Hz and temperature range 303-473 K. The experimental results indicate that the ac conductivity σ_{ac}(ω), dielectric constant ε' and dielectric loss ε" depend on the temperature and frequency. The ac conductivity was found to obey the power law ω^{S} with the frequency exponent S > 1 decreasing with increasing temperature. The present results are compared to the principal theories that describe the universal dielectric response behavior. Values of dielectric constant ε' and dielectric loss ε" were found to be temperature and frequency dependent and the maximum barrier height W_{m} is calculated.

2

Optical Properties of As_{36}Te_{42}Ge_{10}Si_{12} Thin Films

63%

Hegab N., El-Mallah H.

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issue 4

637-642

EN

Thermally evaporated As_{36}Te_{42}Ge_{10}Si_{12} amorphous chalcogenide films were prepared in a vacuum of 10^{-5} Torr on to glass substrates hold at about 300 K during the deposition process. Measurements of the optical properties have been made. The optical transmittance and reflectance spectra of films in the thickness range 155-395 nm were measured in the wavelength λ range 500-2500 nm. The refractive index n, the extinction coefficient k and the absorption coefficient α were calculated for the studied films. It is found that both n and k are independent on the film thickness. The refractive index n has anomalous behavior for the wavelength λ range 500-1500 nm, while it has normal dispersion for the wavelength greater than 1500 nm. The optical energy gap was estimated from absorption coefficient. The allowed optical transitions were found to be nondirect transitions with optical gap of 1.08 eV for the sample under test. The effect of annealing on the obtained optical parameters was also investigated.

3

AC Conductivity and Dielectric Properties οf Amorphous Te_{42}As_{36}Ge_{10}Si_{12} Glass

63%

Hegab N., El-Mallah H.

Acta Physica Polonica A

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2009

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vol. 116

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issue 6

1048-1052

EN

Te_{42}As_{36}Ge_{10}Si_{12} chalcogenide composition was prepared by conventional melt-quenching. The ac conductivity and the dielectric properties were carried out in the frequency range 0.5×10^{3}-4×10^{6} Hz and temperature range 300-423 K. The analysis of the experimental results of the frequency dependence of ac conductivity σ_{ac}(ω) indicates that σ_{ac}(ω) is proportional to ω^{s} where s> 1. The temperature dependence of both ac conductivity and the parameter s is reasonably well interpreted by the correlated barrier hopping model. The maximum barrier height W_{m} calculated from ac conductivity and the density of localized states were determined. Values of dielectric constant ε_{1} and dielectric loss ε_{2} were found to decrease with frequency and increase with temperature. The analysis of dielectric loss leads to determine the barrier height W_{m} and agrees with that proposed by the theory of hopping of charge carriers over potential barrier between charged defect states as suggested by Elliott in case of chalcogenide glasses.

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3 Acta Physica Polonica A

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3 El-Mallah H.

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AC Electrical Conductivity and Dielectric Properties of Perovskite (Pb,Ca)TiO_3 Ceramic

Optical Properties of As_{36}Te_{42}Ge_{10}Si_{12} Thin Films

AC Conductivity and Dielectric Properties οf Amorphous Te_{42}As_{36}Ge_{10}Si_{12} Glass