Mechanochemical synthesis of nano-sized Bi 2 V 0.9 Cu 0.1 O 5.35 powders
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Nano-sized Bi2V0.9Cu0.1O5.35 powders were synthesized via a mechanochemical route from the component oxide mixture. However, a ball-milling duration of over 30 h was needed to ensure a high phase purity. Otherwise, the milled samples had poor sinterability and low sintered density since expansion occurred during sintering.
I. INTRODUCTION
The group of compounds designated as BiMexV1−xO5.5−␦ (Me ⳱ Cu, Ni, Co, Ti, etc.), is very attractive since they have higher ion conductivities, as compared to typical electrolyte systems (e.g., CeO2 and ZrO2).1 Although their applications in solid oxide fuel cells (SOFC) have been ruled out due to easy reduction in reducing atmosphere, BiMexV1−xO5.5−␦ materials are promising candidates for use involving fairly high oxygen pressure, such as oxygen pumps.2,3 Among these compounds, copper-substituted bismuth vanadate with a typical composition of Bi2V0.9Cu0.1O5.35, known as BICUVOX, possesses the highest oxygen ion conductivities at low temperatures.1 BiMexV1−xO5.5−␦ materials have been reported to be difficult to densify because they tend to undergo unusual grain growth during the sintering process.4 It is evident that the conventional solid-state reaction is not a good way to synthesize BiMexV1−xO5.5−␦ powders since this method requires high calcination temperatures, which leads to a larger grain size and hard particle agglomerates of the powders, and hence poor microstructure and properties.5 Unfortunately, however, wet chemical routes also do not seem suitable for obtaining nano-sized BiMexV1−xO5.5−␦ powders. Simner et al.6 reported the phase purity of the material could not be established until calcining temperatures approach 800 °C. Moreover, wet chemical routes usually use expensive and environmentsensitive chemicals, making the preparation process difficult to handle. Therefore, developing new preparation process for synthesizing nano-sized BiMexV1−xO5.5−␦ powders is of academic and practical significance. Recently, a novel high-energy mechanochemical process has been successfully used to prepare a wide range of nano-sized ceramic powders, such as Fe2O3,7 YBCO,8 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0036 J. Mater. Res., Vol. 21, No. 1, Jan 2006
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and ferroelectrics.9,10 The intrinsic characteristic of this technique is to activate the solid-state reaction via mechanical energy instead of heat energy (high temperature). As a result, nano-sized ceramic powders with weak particle agglomerates could be prepared at room temperature. In this paper, we report the synthesis of nanosized BICUVOX powder via a mechanochemical method and its sintering characteristics. II. EXPERIMENTAL
High-purity Bi2O3, V2O5, and CuO (>99.9% purity; Aldrich) were used as starting materials. Before the application of high-energy ball milling, the oxide mixture containing component oxides was thoroughly mixed via a conventional ball milling process, with polypropylene vials and yttria-stabili
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