Correlation of coincidence-site lattice grain boundaries and conductivity for polycrystalline strontium titanate

• Main Authors: Tsai-ling Sun, 孫采翎
• Other Authors: Shao-ju Shih
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/59716848895628620623

碩士 === 國立臺灣科技大學 === 材料科學與工程系 === 102 === Strontium titanate (SrTiO3), has been reported as the candidate of solid-oxide-fuel-cell anode materials to substitute the conventional materials of Ni-doped yttria-stabilized zirconia (YSZ) cermets because of its high chemical and thermal stability. However, the ionic conductivity of SrTiO3 is low comparing to YSZ. In general, space charge of grain boundaries (GBs) trapped oxygen ion to result low ionic conductivity. Based on previous studies, there is no evidence of space charge layers in low energy coincidence-site lattice ?? GBs which do not impede the transport of charge. So far, the reasons of low ?? GBs are abnormal grain growth (losing of low energy GBs) and difficult to orientate because ceramic is too brittle. This study attempts to increase the population of ?? GBs in polycrystalline SrTiO3 for high ionic conductivities. The strategy is to form more (111) faces (?? GB plane) on the surface starting powder by chosen suitable precursor additives. Four types of SrTiO3 powders have been synthesized using spray pyrolysis with strontium nitrate, titanium isopropoxide and additives of nitric acid (HNO3) and the mixtures of HNO3 and hydrogen peroxide (H2O2) with different concentrations. The crystalline structures of SrTiO3 particles were characterized by X-ray diffractometer and Raman spectra. The morphology and size of SrTiO3 particles were observed by using scanning electron microscope (SEM) and transmission electron microscope. And, the microstructures of sintered SrTiO3 bulks were observed by using SEM. The GB orientations were characterized by electron back-scattered diffraction (EBSD). The conductivities were measured by electrochemical impedance spectroscopy and DC method. The microstructural results suggest that the SrTiO3 particles prepared from the additive mixture of HNO3 and H2O2 have a rough surface which contains more (111) surfaces than that of the SrTiO3 particles prepared from HNO3 only. In addition, EBSD and DC measurements show that the SrTiO3 from HNO3 and H2O2 (highest population of ?? GBs) exhibit highest conductivity, which supports our microstructural observations.