5 results
Search Results
Now showing 1 - 5 of 5
Article Citation - WoS: 3Citation - Scopus: 3Effect of Ionic Substitution on the Structural, Dielectric and Electrical Properties of Bismuth Zinc Niobate Ceramics(Korean Assoc Crystal Growth, inc, 2012) Qasrawi, A. F.; Abu Je'ib, Hussein A.; Mergen, A.; Department of Electrical & Electronics EngineeringThe effects of tin substitution on the structural, dielectric and electrical properties of the Bi1.5Zn0.92Nb1.5O6.92 pyrochlore ceramics have been investigated. Tin atoms was substituted in the A (Bi1.5Zn0.46)-site instead of zinc and in the B ((Zn0.46Nb1.5)-site instead of niobium in accordance to the chemical formulae Bi1.5Zn0.92Nb1.5-xO6.92-x/2 and (Bi1.5-x/3Zn0.46-3x/2Snx)(Nb1.5Zn0.46)O-6.92, for 0.00 <= x <= 0.40 and 0.00 <= x <= 0.60, respectively. A relative single phase formation of the structures was possible for x values less than 0.25 and less than 0.10. Pronounced tunability in the dielectric constant values associated with very low dielectric loss are obtainable by Sn substitution. Furthermore, a frequency invariant but linearly varying temperature dependent dielectric constant is observed. The electrical conductivity decreased by two and one order of magnitude for the A and B-site substitutions, respectively. The temperature-dependent conductivity analysis in the temperature region of 300-500 K, reflected the existence of shallow and deep impurity energy levels being created by the doping process.Article Citation - WoS: 12Citation - Scopus: 12Energy Band Gap and Dispersive Optical Parameters in Bi1.5zn0.92< Pyrochlore Ceramics(Elsevier Science Sa, 2010) Qasrawi, A. F.; Mergen, A.The compositional and optical properties of Bi1.5Zn0.92Nb1.5O6.92 Pyrochlore ceramics have been investigated by means of scanning electron microscopy (SEM) and UV-vis spectroscopy, respectively. The SEM spectroscopy revealed that the pyrochlore exhibits a very dense microstructure with single-phase appearance. The absorption spectral analysis in the sharp absorption region revealed an indirect forbidden transitions band gap of 3.30 eV. The room temperature refractive index, which was calculated from the reflectance and transmittance data, allowed the identification of the dispersion and oscillator energies, static and lattice dielectric constants and static refractive index as 26.69 and 3.37 eV, 8.92 and 15.95 and 2.98, respectively. (C) 2010 Elsevier B.V. All rights reserved.Article Citation - WoS: 8Citation - Scopus: 10Structural, Electrical and Dielectric Properties of Bi1.5zn0.92< Pyrochlore Ceramics(Elsevier Sci Ltd, 2012) Qasrawi, A. F.; Mergen, A.The micro-structural, compositional, temperature dependent dielectric and electrical properties of the Bi1.5Zn0.92Nb1.5-xTaxO6.92 solid solution has been investigated. The increasing Ta content from 0.2 to 1.5 caused; single phase formation, a pronounced grain size reduction from similar to 7.0 to 2.5 mu m, sharp decrease in the dielectric constant from 198 to 88 and an increase in the electrical conductivity from 3.16 x 10(-10) to 5.0 x 10(-9) (Omega cm)(-1), respectively. The temperature dependent dielectric constant which is found to be frequency invariant in the frequency range of (0.0-2.0 MHz) exhibited a sharp change in the temperature coefficient of dielectric constant at a (doping independent) critical temperature of 395 K. The analysis of the measured data reflects a promising future for this type of pyrochlore to be used in high voltage passive device applications. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Article Citation - WoS: 1Citation - Scopus: 1Cobalt Doping Effects on the Mechanical and Electrical Parameters of Bi1.5zn0.92< Solid Solution(indian Ceramic Soc, 2014) Qasrawi, A. F.; Jaradat, Haneen N. M.; Mergen, A.The cobalt doping effects on the lattice constant, strain, grain size, dislocation density and electrical conduction are investigated by means of X-ray diffraction and electrical resistivity measurements on the Bi1.5Zn0.92Nb1.5-xCoxO6.92-x (x=0.03-0.20) ceramics, respectively. Increasing cobalt content sharply increases compressing strain and dislocation density and decreases both the lattice constant and the grain size of the pyrochlore. At a doping content of 0.05 new minor phase of ZnO appears. The ZnO grains increase with increasing cobalt content. When the cobalt doping is repeated in accordance with the formula Bi1.5Zn0.92Nb1.5-xCoxO6.92-x, a single phase pyrochlore is obtained with cobalt content up to 0.10. The electrical resistivity analysis reflects increasing activation energy with increasing cobalt content. The cobalt creates an impurity level in the energy gap of the pyrochlore that shifts towards the mid gap converting the extrinsic nature of conductivity to intrinsic at a cobalt content of 0.10.Article Citation - WoS: 3Citation - Scopus: 3Investigation of the Physical Properties of Bi1.5-xcdx< Pyrochlore Ceramics(Springer, 2013) Qasrawi, A. F.; Kmail, Bayan H.; Nazzal, Eman M.; Mergen, A.For the purpose of dielectric parameters tuning Bi1.5Zn0.92Nb1.5O6.92 (BZN) pyrochlore ceramics were subject to cadmium doping in accordance to the chemical formula; Bi1.5-xCdxZn0.92Nb1.5O6.92-x/2 for 0.10 a parts per thousand currency sign x a parts per thousand currency sign 0.50. The main physical properties of the doped samples were investigated by means of X-ray diffraction, scanning electron microscopy associated with energy dispersion spectroscopy, temperature dependent dielectric constant and temperature dependent electrical resistivity to obtain the crystalline structure, the lattice parameter, the relative density, the surface morphology and chemical composition. Optimization of single phase Cd doped samples were possible for x a parts per thousand currency signaEuro parts per thousand 0.14, beyond this limit, ZnO and Zn3Nb2O8 minor phases grow through the structure of the BZN. For samples which exhibit single BZN phase, the dielectric constant, the electrical resistivity and the resistivity activation energy increased with increasing Cd content. The maximum obtainable dielectric constant as 259 and 224 with high signal quality factor of 690 and 1090 at 25 and 200 A degrees C, respectively, was for the sample doped with 0.14 Cd. These values are promising for implantation of BZN in RF and microwave technology as a resonator with high quality signal.
