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IJPAP Vol.43(06) [June 2005] >


Title: Study of dielectric properties of -alumina doped with MnO, CdO and MoO
Authors: Farag, I S Ahmed
Battisha, I K
Rafaay, M M El
Keywords: Dielectric constant
Conductivity
Alumina
Micro-starin
Crystallite
Issue Date: Jun-2005
Publisher: CSIR
IPC CodeG01R27/26
Abstract: The dielectric constant (Ɛ),conductivity (σ) and activation energy (Eg) of -alumina doped with different molar ratios ranging from 0.01 to 0.19 of manganese oxide (MnO), and from 0.01 to 0.16 for both molybdenum oxide (MoO) and cadmium oxide (CdO) were studied. The XRD patterns reveal clearly that the prepared samples, consist of only single phase ( -alumina phase). The crystallite size and micro-strain of the investigated samples were calculated. The crystallite size increases with increasing dopant concentration. But the rate of the crystallite growth differs from one system to another. The value of e has been measured in a frequency range 42 Hz-5 MHz as a function of temperature ranging from 100 to 450°C. The possible explanations and the role of some impurities (mainly Mn, Mo and Cd) are analyzed. The value e of pure sample increases from 9.4 to 10.63 as a function of temperature at constant frequency 1 MHz. In this material, the value of e increases with increase of temperature due to space charge polarization and crystal defects, while it decreases as a function of frequency due to the scattering of charge carriers at high frequencies. From the plots of log σ as a function of the reciprocal of temperature at different frequencies, it has been shown that more than one straight line with different shapes are obtained, indicating different conduction mechanisms at 100 kHz and 1 MHz. An increase in the conductivity with increasing dopant concentration appeared and it could be related to the increase of the charge carriers, which are localized at ions or vacant sites. The activation energies for conduction in the high temperature region are calculated and found to be equal to 0.489, 0.457 and 0.459 eV for 0.01% of Mn, Mo and Cd, cations respectively at constant frequency of 100 kHz. The lower activation energy values for conduction in doped materials may be attributed to a larger charge carrier concentration in them compared to pure a-alumina. The XRD was elucidating to confirm that the obtained phase is a single -alumina phase.
Page(s): 446-458
ISSN: 0975-1041 (Online); 0019-5596 (Print)
Source:IJPAP Vol.43(06) [June 2005]

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