Properties of Ba5Nb4O15 microwave dielectric material by solid-state reaction
| Autor: | Yi-Sheng Li, 李易昇 |
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| Rok vydání: | 2016 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 104 The purpose of this study is to investigate the instability in the solid state sintering process of Ba5Nb4O15 microwave dielectric material quality factor. Ba5Nb4O15 material systems has a high quality factor (Q), high dielectric constant (K), and low temperature coefficient at resonant frequency(τf), which is widely used in research on microwave dielectric materials. However, most papers focus on the relationships between micro-wave properties and extrinsic parameters, few published papers investigates the phe-nomena between sintering temperature and dielectric properties. To prepare Ba5Nb4O15 microwave dielectric material with high quality factor, the study focused on three variants that influenced the quality factor.For most of the ce-ramic material system the sample gets densified with increase in sintering temperature. So, we took temperature as the first variant with temperature values 1190 oC, 1259 oC, 1345 oC, and 1520 oC. There may be a little error in aspect ratio while taking into ac-count for the commercial mass- production, so in order to realize whether the propor-tion of deviation affects the electrical properties, the second variant is the Ba/Nb molar ratio and values are 4.95: 4,5: 4,5.05: 4, The Nb2O5 powder provided by the vendor were of different phase, so the sample prepared from these powder will have different properties. Therefore, third variants is to use different phase of Nb2O5 viz. m-phase Nb2O5, o-phase Nb2O5 and (m + o) phase Nb2O5. This study is divided into three parts, the first part is to study the relation between the sintering temperature and electrical properties of the samples group together by keeping the same molar ratio and varying the phase of the Nb2O5 starting powder. Ab-normal grain growth was observed above 1345 oC temperature, resulting into low den-sified sample and in turn reduced quality factor. Sample sintered at 1259 oC showed better electrical properties.The second part is to investigate using different phase Nb2O5 keeping the molar ratio constant and sintering at 1259 oC. Ba5Nb4O15 samples with m-phase Nb2O5 showed better electrical properties. This can be attributed to the similarity in the structure of Nb2O5 and Ba5Nb4O15 which will ease the atomic diffu-sion and form a complete crystal. The third part is to investigate the prepared samples sintered at 1259 oC using the same m-Nb2O5 powder and varying the molar ratio. Molar ratio with 4.95 showed better electrical properties. So we can know from above three parts that m-phase Nb2O5 is the main reason affecting the quality factor, when we pre-pare using m-phase Nb2O5 at molar ratio 4.95 (Nb rich), we can get better microwave dielectric properties, quality factor (Qf ): 22370, dielectric constant (K): 36.3 |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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