Ordered tructure of Ba(Mg1/3Ta2/3)O3 and Its Measurement on Microwave Dielectric Properties

• Main Author: 田來成
• Other Authors: 蔡大翔
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/15923389347169304121

碩士 === 國立臺灣科技大學 === 化學工程技術研究所 === 86 === 　　The ordering of Ba(Mg1/3Ta2/3)O3 can be altered by substituting La3+ in A-site or Sn4+ in B-site. The superstructure transformation is identified as a variation from 1 : 2 to 1 : 1 ordering. The ordering structure is analyzed, using X-ray diffraction, electron microscopy, Raman spectroscopy, and high resolution electron microscopy. 　　X-ray diffraction results indicate that 1 : 2 ordering in (LaxBa1-x) (Mg1+x/3Ta2-x/3)03 (BLMT) decreases with composition parameter x. The peak intensities of 1 : 2 ordering vanish at x=0.12(2hr) and 0.20(≧24hr). 　　The 1 : 1 ordering appears as x≧0.04, and increases with x. On the other hand, the ordering of (1-x)Ba(Mg1/3Ta2/3)O3-xBaSnOs (BSMT) monotonically decreases with x. 　　Electron diffraction and high resolution electron microscopy show the coexistence of 1 : 2 and 1 : 1 ordering in BLMT(x=0.04-0.08, 2hr sintering ; or x=0.04-0.12, ≧24hr sintering) and BSMT(x=0.05). The micrographs of BLMT indicate that its microdomain size is around 15-30nm at x=O.OO. The domain size does not change very much between x=0.00 to 0.04. The domain size of BLMT x=0.04 is about 10-30nm. The size of coexisting 1 : 1 domain of BLMT x=0.04 is small, around 5-1Onm. The size of 1 : 1 domain increases with x, become 20-30nm at x=0.12. The domain size of BSMT x=0.05 (2hr sintering ) is also 5-10nm. 　　Raman spectra of BLMT specimen show that intensities of three peaks located at 380.9, 427.4, 796.0cm-1 decrease, and their width broaden as x increases. But these three peaks of BLMT x=0.02 become sharp again. Raman peaks of BSMT at 379.2, 426.3, 794.4 also decrease and broaden as x increases. 　　The quality factor of BLMT increases with x and reaches a maximum value of 45000 (at 10 Ghz ) at x=0.04. Quality factor of BLMT decrease with further increasing La content. The dielectric constant of BLMT increases with x. The above results point out that a close relation between ordering structure and dielectric properties of BLMT. A small amount of 1:1 ordering , remaing most of the existing 1:2 ordering, seems to benefit the quality factor and dielectric constant Excessive 1:1 ordering reduces quality factor and slightly enhances the dielectric contant.