| Summary: | 碩士 === 國立臺灣師範大學 === 物理學系 === 96 === The conventional-grown (A’1/3A”2/3)1/2Ti1/2O2 Rutile ceramics (with A’: Mg, Ni, Zn; A”: Nb, Ta) were examined by Raman spectroscopy and extended x-ray absorption find structure (EXAFS) to correlate the microstructure with the microwave dielectric properties. The microwave dielectric properties of (A’1/3A”2/3)1/2Ti1/2O2, such as Qxf value and dielectric constant, are mainly due to the A'and A" atom substitution.
The EXAFS analysis found that the Ti-O bond lengths are the crucial factor for the dielectric constant. The Ti-O bond lengths distances between scattering center and its neighboring atoms are measured, and the shorter the bond length. By comparing the Raman spectra of our samples with the ones of bulk-rutile and nanocrystallien-rutile which are report in literatures, the samples’ Raman experiment data are found closed to nanocrystallien-rutile, we can conclude these samples have nano structure characteristic. Besides, oxygen-octahedral Raman vibration phonon modes are shifted to lower frequencies with the increasing atomic weight of A’ site. The observed phonon shifts are agreed with the calculation that based on the results of EXAFS analyzing. The dielectric constant decreases with the tightening oxygen-octahedral structure. Moreover, the phonon FWHM is strongly correlated with the microwave Qxf value, which indicates the propagation of the microwave EM wave is assisted by the “closed packed” octahedron structure.
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