Spectroscopic Study of xSr(Mg1/3Ta2/3)O3-(1-x)Ba(Mg1/3Ta2/3)O3 Microwave Materials

• Main Authors: I-Hao Chang, 張益豪
• Other Authors: Chih-Ta Chia
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/43504665674179745866

碩士 === 國立臺灣師範大學 === 物理學系 === 97 === X-ray diffraction (XRD), extend x-ray absorption fine structure (EXAFS), Raman scattering, and infrared reflection spectroscopy were adopted to analyze the correlation of microwave properties with the microstructural parameters of xSr(Mg1/3Ta2/3)O3-(1-x)Ba(Mg1/3Ta2/3)O3 perovskite ceramics (xSMT-(1-x)BMT) with x = 0.0 to 1.0. We found the XRD peak (-2 6 0) of monoclinic phase near 2θ = 42°~44.5° appeared when x = 0.25, so the phase transition does occure, but it does not clearly find when it happens by XRD pattern. By EXAFS results, we found a three-stage variation in the χ(R) spectra for the Ta core or the Sr core, and this confirms the minor change of crystal symmetry through the slight displacement of atomic rearrangement as x increases. In Raman scattering experiments, the dominant scattering peaks of monoclinic phase appeared when x ≥ 0.625, and we think it transfers from trigonal symmetry to monoclinic phase for x ≥ 0.625. The shape of peak is not easy to recognize the phase transformation in infrared reflection spectrum, but we can find the at x ≥ 0.625 phase transformation from analyzing shift of phonon peaks. The strong correlation of ordering parameter of B site (Mg and Ta) is obtained by XRD and microwave quality factor such correlation also exists between widths of two Raman A1g(O) phonons and microwave quality factor. After the phase transformation (x ≥ 0.65), the BO6 oxygen octahedra dominate the trend of microwave dielectric constant, so we predict that A site effect on the microwave dielectric properties is remarkable when x ≤ 0.5. The anomaly of the infrared active phonon modes may be connected with microwave dielectric properties, but we need more information from first-principles calculations to get the precise picture of the phase transition by the IR measurements.