Effect of microwave processes on the energy-storage properties of barium strontium titanate glass ceramics
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Barium strontium titanate (BST) glass-ceramics were fabricated via controlled crystallization with different crystallization routes. Effects of the microwave crystallization and microwave treatment on the microstructure and energy storage properties of the glass-ceramics were systematically investigated. Results showed that microwave crystallization can increase the dielectric constant. In addition, it was found that the microwave process had little impact on the crystallinity (about 90 wt%), but preferred the crystallization of SrAl4O7. Most importantly, the dielectric breakdown strength (BDS) of the glass ceramics was significantly improved from 561.3 to 791.4 kV/cm by the microwave crystallization. And it can be further enhanced to 900.0 kV/cm by conventional crystallization combined with microwave treatment. The corresponding energy densities of samples derived from the microwave processes were increased to 1.05 and 1.13 J/cm3, respectively, compared with the sample fabricated by the conventional crystallization route (0.47 J/cm3).
I. INTRODUCTION
BaTiO3-based ferroelectric glass ceramic systems have been attracting an increasingly fundamental and practical interest because of their low porosity, high dielectric constant, and high dielectric breakdown strengths (BDS). The applications cover the pulse power systems, high-power microwave systems, hybrid vehicles, electric ships, etc. Actually, to achieve high stored electric energy per unit volume is up to now still a challenging task in glass ceramic systems. Dielectric constant and BDS are two important parameters, wherein the BDS is playing an important role in determining the energy storage capability of materials. The BDS of glass ceramics was affected by several factors, such as degree of crystallinity, accumulation of bulk charge, and interfacial area.1 In contrast to the conventional powder-processed ferroelectric ceramics, glass-ceramics possess a uniformity of microstructure and an almost zero porosity, which provide unique attributes for high-energy density capacitor applications.2 To date, within the BaTiO3-based ferroelectric glass ceramic systems available, barium strontium titanate glass ceramic is one of the most widely exploited and extensively studied materials, because of the well-controlled Curie point of BST glass-ceramics by adjusting Ba/Sr ratio, so that the materials with the paraelectric state can maintain good reproductivity at high electric fields.3 Now, various processing techniques have been utilized to modify the properties of BST glass ceramics, such as internal nucleation of glass monoliths,4 sintering and crystallization of Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.386 J. Mater. Res., Vol. 29, No. 2, Jan 28, 2014
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II. EXPERIMENTAL PROCEDURE
BST-based glass samples used in this study were prepared with the composition of 14.8BaCO3, 22.2SrCO3, 29TiO2, 12Al2O3, and 22SiO2 (mol%). A powder containing appropriate constituents was ball milled for 20 h in
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