Structural Optical and Microwave Dielectric Properties of Some Tungstates and Molybdates

Abstract

Metal tungstates and molybdates having the general formula of ABO4 (A=Ba, newlineSr, Ca, Zn, Mg, Cu and B= W, Mo) have been widely investigated for their newlinemultifunctional applications. They are commonly used in phosphors, scintillation newlinedetectors, photonics, microwaves, optoelectronics, laser materials, and optical newlinemodulation devices. Based on the ionic radius of the cation in A2+ newlinesites, this family of newlinethe compound can crystallize in either scheelite or wolframite structure. The main newlineobjective of the present thesis was the systematic investigation of structural, optical, newlineand microwave dielectric properties of ABO4 tungstates and molybdates ceramics. The newlinesolid-state reaction method was taken into account to synthesize different tungstates newlineand molybdates ceramics, followed by controlled high-temperature sintering for newlineachieving high relative density. These ceramics were structurally characterized by newlineXRD, Raman spectroscopy, FTIR and XAS, spectroscopy. Investigation of newlinemicrostructural analysis was done by SEM. Calculation of optical band gap was done newlineusing UV-Vis spectrophotometer in diffuse reflection mode. PL measurement was newlineperformed through a fluorescence luminescence spectrophotometer in which a xenon newlinelamp is used as an excitation source. The dielectric properties were analyzed by the newlineHakki-Coleman technique. All electronic and absorption properties investigations for newlineABO4 ceramics were performed by employing density functional theory (DFT). The newlineproposed structural models were built based on the Rietveld refinement of XRD data. newlineOptimization and post properties calculations were carried out by using the Vienna Ab newlineInitio Simulation Package (VASP) code. The core-valence interaction was described newlineby a projector augmented wave (PAW) approach. Generalized Gradient Approximation newline(GGA) with Perdew-Burke-Ernzerhof (PBE) functional were used for the exchange and newlinecorrelation effect of the electrons. All peaks in diffraction patterns in ABO4 are newlinecorresponding to the monophasic nature of ceramics. In the XRD