X-ray photoelectron spectroscopy and electrical properties studies of La2O3-doped strontium titanate ceramics prepared by sol-precipitation method

Author： Yang W-D.

Publisher： Springer Publishing Company

ISSN： 0022-2461

Source： Journal of Materials Science, Vol.34, Iss.14, 1999-07, pp. : 3533-3544

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Abstract

X-ray photoelectron spectroscopy has been used to investigate the existence of Ti^3+ on the surface of La_2O_3-doped strontium titanate and to determine its surface characteristics. The surfaces, having Sr/Ti ratios significantly varying from the stoichiometric ratio, revealed the presence of carbon and suggested the presence of hydroxyl groups on the surface, whose concentration largely decreased in the bulk. Ti^3+ species existed as a function of the sintering conditions and were detected on the surface of (La, Sr)TiO_3 sintered in air or in N_2 by natural cooling. These samples had a lower electrical resistivity, especially when sintered in a N_2 atmosphere. The surfaces of air oxidized SrTiO_3 and quenched from high temperature contained no detectable amount of Ti^3+, resulting in higher resistivity. However, the N_2-sintered samples were dark blue in color and exhibited lower resistivity, semiconductivity, and lower valence oxidation state Ti existed when sintered above 1350°C.