Tungsten doping effects on the properties of Bi1.5Zn0.92Nb1.5O6.92 (BZN) ceramics رسالة ماجستير

Abstract

In this thesis, the tungsten doping effects on the morphological, structural, compositional, electrical and optical properties of the bismuth zinc niobium oxide pyrochlore ceramics in accordance with the chemical formula Bi1.5Zn0.92Nb1.5-6x/5WxO6.92 are investigated. The tungsten content is varied in the range of 0.10-0.18. While the structural properties were investigated by means of X-ray diffraction where a new minor phase has appeared indicating the solubility limit at x= 0.18, the morphology and energy dispersive X-ray analysis confirms this result. The temperature dependent XRD analysis was employed to determine the temperature effects on the lattice constant, grain size, micro strain, dislocation density and degree of orientation. In addition, the room temperature impedance spectra are recorded in the frequency range from 0.01 to 1.8 GHz. The physical parameters of capacitance, conductance, reflection coefficient, return loss and voltage standing wave ratio that are needed to show the ability of using the W-BZN as an active resonator in telecommunication technology were investigated. The effect of W content on the electrical resistivity is evaluated by dc measurements in the temperature range of 298-487 K. The activation energy is less than half of the energy band gap indicating the extrinsic nature of conduction. The energy band gap is found to be of direct allowed type.