Browsing by Author "Mergen, A."
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Article Citation Count: 1Cobalt Doping Effects on the Mechanical and Electrical Parameters of Bi1.5Zn0.92Nb1.5O6.92 Solid Solution(indian Ceramic Soc, 2014) Qasrawı, Atef Fayez Hasan; Jaradat, Haneen N. M.; Mergen, A.; Department of Electrical & Electronics EngineeringThe 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 Count: 3Dielectric dispersion and energy band gap of Bi1.5-xSmxZn0.92Nb1.5O6.92 solid solution(Elsevier Science Bv, 2014) Qasrawı, Atef Fayez Hasan; Mergen, A.; Department of Electrical & Electronics EngineeringThe optical transmittance and reflectance spectra of samarium doped bismuth-zinc-niobium-oxide (BZN) pyrochlore ceramics are investigated in the wavelength range of 200-1050 nm (200-1500 THz). The Sm content in the Bi1.5-xSmxZn0.92Nb1.5O6.92 solid solution significantly alters the optical properties. Therefore, increasing the Sm doping ratio from x=0.10 to x=0.13 decreased the indirect forbidden energy band gap from 3.60 to 3.05 eV. In addition, above 350 THz, increasing the Sin content decreases the dielectric constant values and alters the dielectric dispersion parameters. The dielectric spectra which were evaluated in the frequency range of 200-1500 THz reflected a sharp decrease in the dielectric constant with increasing frequency clown to 358 THz. The spectra reflected a resonance peak at this frequency. Such resonance spectrum is promising for technological applications as it is close to the illumination of 870 am IR lasers that are used in optical communications. The calculated oscillator (E-o) and dispersion (E-d) energies near that critical range (375-425 THz) reflected an increase in both E-o and E-d with increasing Sm content. (C) 2014 Elsevier B.V. All rights reserved.Article Citation Count: 4Effect of yttrium solubility on the structural and optical properties of Bi1.5-xYxZn0.92Nb1.5O6.92 pyrochlore ceramics(Elsevier Sci Ltd, 2013) Qasrawı, Atef Fayez Hasan; Mergen, A.; Department of Electrical & Electronics EngineeringIn this article, the yttrium solubility effects on the structural, dielectric and optical properties of the Bi1.5-xYxZn0.92Nb1.5O6.92 (Y-BZN) solid solutions are investigated. The yttrium content (x) was varied in the range of 0.04-0.6. The scanning electron microscopy and energy dispersion analysis have shown that the single phase of the yttrium doped pyrochlore is possible up to yttrium content of 0.06. At x=0.07 YNbO4 minor phase appears and at x=0.08 YNbO4 and ZnO dominates in the Y-BZN. Due to the very rare amount and the random distribution of the minor phases in the pyrochlore, the X-ray diffraction technique was not able to detect these minor phases at low yttrium doping levels. While the nonstoichiometric phase evaluated at x=0.07 displayed no role on the relative density, the dielectric constant, dielectric loss, the temperature coefficient of dielectric constant, the absorbance and the energy band gap are observed to be sharply altered. The energy band gap of the pure BZN widened from 3.30 eV to 3.60 eV when the BZN was doped with Y content of 0.04. It then sharply shrunk to 2.75 eV for Y content of 0.07. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Article Citation Count: 2Electrical characterization of Bi1.50-xYxZn0.92Nb1.5O6.92 varactors(World Scientific Publ Co Pte Ltd, 2014) Qasrawı, Atef Fayez Hasan; Abu Muis, Khalil O.; Abu Al Rob, Osama H.; Mergen, A.; Department of Electrical & Electronics EngineeringThe electrical properties of yttrium doped bismuth zinc niobium oxide (BZN) pyrochlore ceramics are explored by means of temperature dependent electrical conductivity dielectric constant and capacitance spectra in the frequency range of 0-3 GHz. It is observed that the doped BZN exhibit a conductivity type conversion from intrinsic to extrinsic as the doping content increased from 0.04 to 0.06. The thermal energy bandgap of the intrinsic type is 3.45 eV. The pyrochlore is observed to exhibit a dielectric breakdown at 395 K. In addition, a negative capacitance (NC) spectrum with main resonance peak position of 23.2 MHz is detected. The NC effect is ascribed to the increased polarization and the availability of more free carriers in the device. When the NC signal amplitude is attenuated in the range of 0-20 dBm at 50 MHz and 150 MHz, wide tunability is monitored. Such characteristics of the Y-doped BZN are attractive for using them to cancel the positive parasitic capacitance of electronic circuits. The canceling of parasitic capacitance improves the high frequency performance of filter inductors and reduces the common mode noise of the resonance signal.Article Citation Count: 4Electrical conductivity and capacitance spectra of Bi1.37Sm0.13Zn0.92Nb1.50O6.92 pyrochlore ceramic in the range of 0-3 GHz(World Scientific Publ Co Pte Ltd, 2014) Qasrawı, Atef Fayez Hasan; Bzour, Faten M.; Nazzal, Eman O.; Mergen, A.; Department of Electrical & Electronics EngineeringIn this work, the electrical properties of samarium-doped bismuth niobium zinc oxide (Sm-doped BZN) pyrochlore ceramics are investigated by means of temperature dependent electrical conductivity and capacitance spectroscopy in the frequency range of 0-3 GHz. It was observed that the novel dielectric Sm-BZN ceramic exhibits a temperature and electric field dependent dielectric breakdown. When measured at 300 K, the breakdown electric field is 1.12 kV/cm and when heated the breakdown temperature is similar to 420 K. The pyrochlore is thermally active above 440K with conductivity activation energy of 1.37 eV. In addition, the room temperature capacitance spectra reflected a resonance-antiresonance switching property at 53MHz when subjected to an AC signal of low power of 5 dBm. Furthermore, when the Sm-BZN ceramics are used as microwave cavity and tested in the frequency range of 1.0-3.0 GHz, the cavity behaves as low pass filter with wide tunability up to a frequency of 1.91 GHz. At this frequency it behaves as a band rejection filter that blocks waves of 1.91 GHz and 2.57 GHz frequencies. These properties of the Sm-doped BZN are promising as they indicate the usability of the ceramics in digital electronic circuits as resonant microwave cavities suitable for the production of low pass/rejection band filters.Article Citation Count: 12Energy band gap and dispersive optical parameters in Bi1.5Zn0.92Nb1.5O6.92 pyrochlore ceramics(Elsevier Science Sa, 2010) Qasrawı, Atef Fayez Hasan; Mergen, A.; Department of Electrical & Electronics EngineeringThe 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 Count: 3Investigation of the physical properties of Bi1.5-xCdxZn0.92Nb1.5O6.92-x/2 pyrochlore ceramics(Springer, 2013) Qasrawı, Atef Fayez Hasan; Kmail, Bayan H.; Nazzal, Eman M.; Mergen, A.; Department of Electrical & Electronics EngineeringFor 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.Article Citation Count: 5Mechanical and electrical properties of Bi1.5-xLaxZn0.92Nb1.5O6.92 pyrochlore ceramics(Springer, 2016) Qasrawı, Atef Fayez Hasan; Kmail, Renal R. N.; Mergen, A.; Genc, Seval; Department of Electrical & Electronics EngineeringThe physical properties of Bi1.5-xLaxZn0.92Nb1.5O6.92 solid solutions are investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersion X-ray spectroscopy (EDS), and temperature dependent relative permittivity and electrical resistivity measurements. The La content which was varied from 0.10 to 0.60 is found to be solvable up to 0.21. Further increase in the amount of the La content caused the appearance of Bi0.4La0.6O1.5, LaNbO4, and ZnO minor phases in the pyrochlore matrix. While the lattice parameter and the theoretical, bulk and relative density are hardly affected by the increase in the La content, the strain, the dislocation density and the crystallite size are remarkably varied. The relative permittivity and temperature coefficient of relative permittivity are found to be sensitive to the La-Content. The electrical resistivity is observed to be temperature invariant below 390 K. It exhibits an insulator-semiconductor transition property at a critical temperature that increases with the increasing La content. Such observation is assigned to the increase in the dislocation density, which arises from the increment in the La content. The activation energies of the doped ceramics, which are determined from the electrical resistivity analysis are found to be similar to 1.12-1.00 eV.Article Citation Count: 3Physical properties of neodymium tin oxide pyrochlore ceramics(de Gruyter Poland Sp Zoo, 2017) Qasrawı, Atef Fayez Hasan; Qasrawi, A. F.; Yumusak, G.; Mergen, A.; Department of Electrical & Electronics EngineeringIn this work, physical properties of neodymium tin oxide pyrochlore ceramics prepared by solid state reaction technique are investigated by means of X-ray diffraction, scanning electron microscopy, ultraviolet-visible light (UV-Vis) spectrophotometry and temperature dependent electrical resistivity measurements. The pyrochlore is observed to have a cubic FCC crystal lattice with lattice parameter of 10.578 angstrom. The planes of the cubic cell are best oriented in the [2 2 2] direction. From the X-ray, the UV-Vis spectrophotometry and the electrical resistivity data analysis, the grain size, strain, dislocation density, optical and thermal energy band gaps, localized energy band tail states and resistivity activation energies are determined and discussed. The pyrochlore is observed to have an optical energy band gap of similar to 3.40 eV. This value corresponds to 365 nm UV light spectra which nominates the neodymium tin oxide pyrochlore ceramics for the use as UV sensors.Article Citation Count: 6Physical properties of the Bi1.5Zn0.92-2xHfxNb1.5O6.92 solid solutions(Elsevier Sci Ltd, 2016) Qasrawı, Atef Fayez Hasan; Qasrawi, A. F.; Mergen, A.; Department of Electrical & Electronics EngineeringThe Hf doping effect on the structural, compositional, optical, electrical and dielectric properties of the bismuth-zinc-niobium oxide pyrochlore ceramics is explored by means of scanning electron microscopy, energy dispersive X-ray spectroscopy, ultraviolet-visible light spectroscopy in the wavelength range of 200-1100 nm, temperature dependent electrical resistivity measurements in the range of 300-460 K and dielectric spectroscopy in the frequency range of 0.1-1.0 GHz. The optimum solubility limit in the Bi1.5Zn0.92-2xHfxNb1.5O6.92 solid solution is observed for the Hf content of 0.06. Increasing the Hf content from 0.03 to 0.06 decreased the room temperature, lattice constant, strain, dislocation density, optical energy band gap and electrical resistivity. It also increased the crystallite size and the dielectric constant. The energy band gap of the pure BZN (3.30 eV) decreased to 2.21 and reached 2.10 eV as the Hf content increased from 0.03 to 0.06. This behavior of the BZN suggests its suitability for optical applications of the visible region of light like photovoltaic devices. In addition, the remarkable increase in the dielectric constant from 258 to 280 and 456 nominates the Hf doped pyrochlore for passive mode operation devices like microwave capacitors. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Article Citation Count: 9Structural, electrical and dielectric properties of Bi1.5Zn0.92Nb1.5-xTaxO6.92 pyrochlore ceramics(Elsevier Sci Ltd, 2012) Qasrawı, Atef Fayez Hasan; Mergen, A.; Department of Electrical & Electronics EngineeringThe 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 Count: 3Structural, Optical and Electrical Properties of Bi1.5Zn0.92Nb1.5-6x/5WxO6.92 Pyrochlore Ceramics(Univ Fed Sao Carlos, dept Engenharia Materials, 2021) Qasrawı, Atef Fayez Hasan; Abdalghafour, Mays A.; Mergen, A.; Department of Electrical & Electronics EngineeringHerein, the structural, morphological, compositional, optical, electrical and dielectric properties of Bi1.5Zn0.92Nb1.5-6x/5WxO6.92 (BZN) solid solutions are reported. Tungsten substituted BZN ceramics which are fabricated by the solid state reaction technique exhibited solubility limits at substitution level below x=0.18. Remarkable engineering in the structural, optical, electrical and dielectric properties of the pyrochlore ceramics is achieved via W substitution. Namely, shrinkage in both of the lattice parameters and in the energy band gap accompanied with decrease in the microstrain, in the dielectric constant and in the electrical resistivity is observed upon increasing the W content below the solubility limit. The increase in the W content in the BZN ceramics enhances the densification of the pyrochlore and leads to higher light absorbability and larger crystallites growth. The temperature dependent electrical resistivity measurements has also shown that the pyrochlore exhibit thermal stability below 380 K.Article Citation Count: 10Structural, optical, electrical and dielectric properties of Bi1.5Zn0.92Nb1.5-xNixO6.92-3x/2 solid solution(Taylor & Francis Ltd, 2012) Qasrawı, Atef Fayez Hasan; Nazzal, E. M.; Mergen, A.; Department of Electrical & Electronics EngineeringThe effects of Ni content on the structural, optical, dielectric and electrical properties of Bi1.5Zn0.92Nb1.5O6.92 pyrochlore ceramics have been investigated. Nickel atoms were inserted into pure samples in accordance to the composition Bi1.5Zn0.92Nb1.5-xNixO6.92-3x/2, with x varying from 0.07 to 0.40. The structural analysis revealed that a single phase of the pyrochlore compound can be obtained for x values of 0.07 and 0.10 only. Further increase in Ni caused the appearance of multiple phases. The optical energy band gaps are determined as 3.30, 3.35 and 3.52 eV for Ni content of 0.00, 0.07 and 0.10 respectively. The temperature dependent electrical resistivity and the frequency dependent capacitance are observed to increase with increasing Ni content. The resonance frequency, which was determined from the capacitance-frequency dependence, was observed to shift from 12.14 to 10.47 kHz as the x values increase from 0.00 to 0.10 respectively.Article Citation Count: 18Synthesis and characterization of Bi1.5Zn0.92Nb1.5-xSnxO6.92-x/2 pyrochlore ceramics(Elsevier Sci Ltd, 2012) Qasrawı, Atef Fayez Hasan; Kmail, Bayan H.; Mergen, A.; Department of Electrical & Electronics EngineeringThe morphological, compositional, structural, dielectric and electrical properties of Bi1.5Zn0.92Nb1.5-xSnxO6.92-x/2 ceramics have been investigated by means of scanning electron microscopy (SEM), X-ray energy dispersion spectroscopy (EDS), X-ray diffraction (XRD), temperature and frequency dependent dielectric constant and temperature dependent conductivity measurements for Sn-contents in the range of 0.00 <= x <= 0.60. It was shown that single phase of the pyrochlore ceramics can only be obtained for x <= 0.25. Above this value a ZnO phase appeared in the XRD patterns and SEM micrographs as well. An increase in the lattice constant and in the temperature coefficient of dielectric constant and a decrease in the dielectric constant values with increasing Sn content was observed for the ceramics which exhibited a single phase formation. A temperature dependent but frequency invariant dielectric constant was observed for this type of ceramics. The lowest electrical conductivity and highest dielectric constant was observed for the sample which contains 0.06 Sn. The Bi1.5Zn0.92Nb1.5-xSnxO6.92-x/2 pyrochlore ceramic conductivities are thermally active above 395 K. For temperatures greater than 395 K, the conductivity activation energy which was found to be 0.415 eV for the pure sample increased to 1.371 eV when sample was doped with 0.06 Sn. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Article Citation Count: 1Tungsten doped Bi1.5Zn0.92Nb1.5O6.92 ceramics designed as radio/microwave band pass/reject filters(Wiley, 2021) Qasrawı, Atef Fayez Hasan; Abdalghafour, Mays A.; Mergen, A.; Department of Electrical & Electronics EngineeringHerein, radiowave/microwave bandpass/reject filters are fabricated from the tungsten doped Bi1.5Zn0.92Nb1.5-6x/5WxO6.92 (W-BZN) pyrochlore ceramics. The W-BZN band filters are prepared by the solid state reaction technique and subjected to X-ray diffraction (XRD) and impedance spectroscopy analyses. It was shown that the W-BZN filters can display negative capacitance effects accompanied with resonance-antiresonance oscillations. The calculations of the reflection coefficient parameter (S-11), the return loss (L-r) and the voltage standing wave ratios (VSWR) in the frequency domain of 0.01 to 1.80 GHz, has shown that the W-BZN device can perform as microwave cavities at two notch frequency values of 0.44 and 1.53 GHz. W-BZN devices can also be nominated as noise reducers and radiowave/microwave signal receivers suitable for telecommunication technology.