Methods of formation of Niobium Tin Oxide compound and some related applications رسالة ماجستير

Abstract

In this thesis, we have prepared SnNb:O compounds by three methods. Namely, by the laser welding (LW( technique under Na atmosphere, by solid state reaction )SSR) technique and by thermal evaporation (TE) technique. The produced samples are studied by means of X-ray diffraction, impedance spectroscopy and optical spectrophotometry techniques. The preparation method by SSR technique included sintering process at various temperatures in the range of 1000-1300°C for sintering times in the ranges of 2- 6 hrs. The XRD analysis for the samples has shown that; samples prepared by LW and SSR techniques are of polycrystalline nature. On the other hand, deposited Glass/Nb2Os/SnOa thin films displayed amorphous structure. In general, SnNb:0 samples display multiphase structure. The dominant structural phase depends on the preparation technique and/or sintering temperature. It is also observed that, the structural parameters including the crystallite sizes, the microstains, the stacking faults and defect densities are highly influenced by the preparation method. Samples of the largest crystallite size, least strain and least defect density are obtained by the SSR technique at sintering temperature 1300°C for 3 hrs. Single phase of the orthorhombic SnNb2Ox is achieved by the same method at 1300°C being sintered for 3 hrs. On the other hand, the impedance spectroscopy measurements have shown that samples prepared by LW technique display the highest impedance in the frequency domain of 10-1800 MHz. Negative conductivity is observed for samples prepared by the SSR and LW techniques near 1500 MHz. While the capacitance spectrum of the sample prepared by

laser welding technique show resonance — antiresonance phenomena in the microwave frequency domain. These prepared by SSR and TE techniques showed the same phenomena in the radiowave range of frequency. Modeling of the capacitance and conductivity spectra indicated the domination of quantum mechanical tunneling and correlated barrier hopping conduction in the samples. The optical measurements which were possible for samples prepared by TE technique indicated the existence of two energy band gaps being dominant above and below 3.0 e٧V, respectively. In addition, the Drude — Lorentz modeling of the conductivity spectra of the samples prepared by TE technique have shown that the drift mobility of thin film samples increased upon stacking of Glass/Nb:Os with SnO2. The stacked layers of the films display

plasmon frequency values that suits for microwave resonators.