| Summary: | 碩士 === 國立東華大學 === 應用物理研究所 === 95 === The perovskite oxide of LaNiO3 is commonly used as an electrode for high-temperature oxide fuel cells, catalysts, alcohol detectors etc. The LaNiO3 phase is unstable at high temperatures, as it tends to decompose and disintegrate into La2NiO4 and NiO phases. In order to grow a dense and single phase of LaNiO3 bulk sample, a chemical stabilization method by adding various dopants into LaNiO3 was attempted. In this study, the experiment consists of two parts. The first part is the study of high-temperature stability of B-site doped LaNiO3, prepared by a conventional mixed oxide method with Zr, Ti, Mg, Nb, Cu, Fe, and Mn partially substituting for Ni. It was found that Fe and Mn are the only dopants to have the stable (113) phase at sintering temperature of 1400 oC. In the second part, the A-site/B-site substituted La(Ni,Fe)O3 bulks with Ag, Pb and Nd on the A sites and Mn and Ga on the B sites were prepared by a chemical route. The temperature-dependent electrical resistivity ρ(T) of the resulting compounds was investigated to study the effects of substitution in La(Ni,Fe)O3.
The measurements of ρ(T) show that all the A-site/B-site substituted La(Ni,Fe)O3 have a semiconducting character. The lnρ versus T-1/4 plots show a linear relationship in the temperature rage of 150 to 300 K, indicating that the electrical transport of these compounds is governed by the Mott’s variable range hopping (VRH) mechanism. The activation energies for the charge carriers can be estimated from the slopes of the lnρ vs. T-1/4 plots. The variations of room–temperature resistivity and activation energy of these compounds could be satisfactorily rationalized by considering the tolerance factor in affecting the Ni-O-Ni bonding angle and the resulting change in the energy band structure
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