Solubility of lanthanum in strontium titanate in oxygen-rich atmospheres

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Moos, Ralf ; Bischoff, Tilman ; Menesklou, Wolfgang ; Härdtl, Karl Heinz:
Solubility of lanthanum in strontium titanate in oxygen-rich atmospheres.
In: Journal of Materials Science. Bd. 32 (1997) Heft 16 . - S. 4247-4252.
ISSN 1573-4803
DOI: https://doi.org/10.1023/A:1018647117607

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Abstract

Perovskite (ABO3)-type lanthanum substituted strontium titanate ceramics (lanthanum content x), which had been sintered in pure oxygen at 1400 °C, were investigated from x = 0 up to x = 0.6 by light optical and scanning electron microscopic means in conjunction with X-ray analysis, X-ray diffraction, and pyconometry in order to determine the mechanism being responsible for the compensation of the electronic excess charge resulting from the "donor" lanthanum. A pure strontium vacancy compensation mechanism was observed for lanthanum contents up to x = 0.3. Above x = 0.4 titanium vacancies occur additionally but their concentration remains negligible compared to the predominating strontium vacancies. No indication of a solubility limit of lanthanum at x = 0.4, as stated in former works was observed. At x = 0.5 and 0.6 the lattice structure was found to be slightly distorted, tetragonally and orthorhombically, respectively. The lattice parameter obeys Vegard’s law up to the end member La2/3□1/3TiO3 (□: vacant site). These results were completely confirmed by pycnometry data.