Browsing by Author "Hennings, D"

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Effects of A/B cation ratio on the microstructure and lifetime of (Ba1-xCax)(z)(Ti0.99-y ZryMn0.01)O-3 (BCTZM) sintered in reducing atmosphere
(2000-03-01)
Lee, WH
;
Tseng, TY
;
Hennings, D
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Microstructure and dielectric properties of (Ba1-xCax)(z)(Ti0.99-yZry Mn-0.01)O-3 (BCTZM) with various cation ratios (A/B) sintered in reducing atmosphere and then annealed to reoxidize the ceramic bodies were investigated. With decreasing A/B cation ratio, concurrent with the grain size reduction, the insulation resistance and lifetime of the BCTZM are both increased. The degradation of insulation resistance is closely related to oxygen partial pressure used during annealing and the resulting microstructure of the ceramics. Within the same volume, the specimen with fine grain size provides more grain boundaries, in comparison to large grain size specimens, which helps in providing an efficient diffusion pathway for oxygen during annealing. The result of oxidation of the Mn, that is, a change in the valence state of Mn from Mn+2 to Mn+3 is confirmed from thermogravimetric analysis and electron paramagnetic resonance analysis.
Effects of ceramic processing parameters on the microstructure and dielectric properties of (Ba1-xCax)(Ti0.99-y, ZryMn0.01)O-3 sintered in a reducing atmosphere
(2001-02-01)
Lee, WH
;
Tseng, TY
;
Hennings, D
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The effect of A/B ratio, sintering temperature, and oxygen partial pressure on microstructure and ceramic dielectric properties of 1 mol % MnO2 doped (Ba,Ca)(Ti,Zr,)O-3 sintered in a reducing atmosphere were investigated. Microstructure is found to be closely related to processing parameters. With decreasing A/B ratio, decreasing oxygen partial pressure and increasing sintering temperature, grain growth is enhanced. Concurrent with the grain size reduction, the crystal structure transformed from tetragonal to pseudocubic at room temperature and the dielectric constant, the dissipation factor and Curie point all decreased. However, the effects of grain size give a marked discrepancy on breakdown. The effect of A/B ratio and sintering temperature both suggest that breakdown voltage is decreased with increasing grain size. However, the breakdown voltage in relation to grain size by changing the oxygen partial pressure seems to show no significant difference. (C) 2001 Kluwer Academic Publishers.
Surface modification of Dy2O3-Nb2O5 dope mix for dielectric materials in aqueous dispersion
(2000-06-01)
Lee, WH
;
Tseng, TY
;
Hennings, D
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The electrokinetic mismatch between the basic dielectric compound (Ba,Ca)(Ti,Zr)O-3 (BCTZ) and Dy2O3-Nb2O5 dope mix in aqueous suspensions has been improved by a pre-firing and milling treatment of the dope mix. Pre-fired dope mix showed a much higher zeta potential which resulted in a drastic improvement of the particle dispersion in aqueous slurries. By use of surface-modified dope mix the homogeneity of the micro structure of multilayer ceramic capacitors is improved and the break-down voltage of thin (7 mu m) dielectric layers increased. The results observed indicate the critical influence of the micro structural homogeneity on the breakdown voltage of MLCCs. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.