SrxBa1-x-Nb2O6 Glass-Ceramics

Autor: Cheng-Jung Wang, 王振榮
Rok vydání: 1999
Druh dokumentu: 學位論文 ; thesis
Popis: 87
In this thesis, glass-ceramics containing tungsten bronze phase SrxBa1-xNb2O6（SBN）were prepared. Glass formation region, crystal morphology, crystallization behavior, crystal-growth kinetics, and dielectric properties of the glass-ceramics were discussed. The glass crystallization temperature and softening temperature were determined by DTA and TMA, respectively. Qualitative and quantitative analysis of the SBN phase were conducted by XRD. SEM observed the microstructure of the glass-ceramics. The composition of the SBN phase was determined by EPMA. An LCR meter measured the dielectric properties of the glass-ceramics. The parent glasses were prepared by melting powder mixtures of SrCO3、BaCO3、Nb2O5 and SiO2, then pouring on the copper plate. Transparent glasses can be obtained in some SrO-BaO-Nb2O5-SiO2 compositions. Among them, some compositions revealed SBN as the primary crystalline phase after proper crystallization heat-treatment. The SBN phase showed both surface and bulk crystallization. For the samples heated at low temperature for long period of time (e.g., 825℃/24 h, 850℃/6-9 h, and 865℃/6 h) or at high temperatures for a short period of time (e.g., 880 - 925℃/≦2h), the layer thickness of the surface-nucleated secondary phase(s) was about 40 µm. When the heating temperature/time was further increased, the secondary phase(s) grew into the inner region of the samples by crystallization of the residual glass. The SBN crystal showed a three-dimensional dendritic morphology. When the heating temperature was increased, the size and the growth rate of the SBN crystal were obviously increased. The dielectric constants of the crystallized samples were obviously higher than that of the parent glass. The dielectric constant increased with the increase in the SBN content in the glass-ceramics.
Databáze: Networked Digital Library of Theses & Dissertations
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