The effect of cation non-stoichiometry in LaNbO₄ materials

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• 作者：Guttorm E. Syvertsen^a ; Anna Magras&oacute ; ^b ; Reidar Haugsrud^b ; Mari-Ann Einarsrud^a ; Tor Grande^a ; ^{tor.grande@material.ntnu.no}
• 关键词：LaNbO4 ; Proton conductivity ; Phase purity ; Solid solubility
• 刊名：International Journal of Hydrogen Energy
• 出版年：2012
• 期刊代码：42_03603199
• 类别：ch
• 出版时间：May, 2012
• 卷：37
• 期：9
• 页码：8017-8026
• 文件大小：1801 K

摘要

The effect of cation non-stoichiometry in LaNbO₄ was investigated by impregnating nano-crystalline LaNbO₄ with small amounts of La³⁺, Nb⁵⁺ and Ca²⁺ oxide precursors. The sintering properties of the modified LaNbO₄ powders were investigated by dilatometry, and the microstructure and phase composition were studied by electron microscopy and X-ray diffraction. The electrical properties of the materials were studied by 4-point DC-conductivity and 2-point 4-wire AC-conductivity at elevated temperatures in controlled atmosphere. Minor variations in the cation stoichiometry were shown to have a pronounced effect on both the sintering properties as well as the electrical conductivity. Addition of CaO, which introduced secondary phases above 0.25 mol%CaO, increased the sintering temperature and improved the conductivity of the materials. La₂O₃- and Nb₂O₅-excess materials did not show large variation in the electrical conductivity relative to pure LaNbO₄, while the sintering properties were strongly affected by the nominal La/Nb ratio in LaNbO₄. The present findings demonstrate the sensitivity of cation non-stoichiometry in materials with limited solid solubility.