Topotaxial formation of titanium-rich barium titanates during solid state reactions on (110) TiO2 (rutile) and (001) BaTiO3 single crystals |
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Authors: | A. Lotnyk A. Graff S. Senz N.D. Zakharov D. Hesse |
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Affiliation: | aMax Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle, Germany;bFraunhofer Institute for Mechanics of Materials IWM, Heideallee 19, 06120 Halle, Germany |
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Abstract: | The orientation relationships of Ti-rich barium titanate phases formed by solid state reactions at high temperatures were studied using (110) TiO2 (rutile) and (001) BaTiO3 single-crystal substrates. Well-oriented Ba6Ti17O40 islands were observed after a vapor–solid reaction of a BaO quantity equivalent to a nominal BaO film thickness of 1 nm with the TiO2 substrate, whereas a thin film consisting of well-oriented BaTiO3 and Ba6Ti17O40 grains was formed after vapor–solid reaction of a BaO quantity equivalent to a nominal BaO film thickness of 50 nm with the rutile substrate. A topotaxial orientation relationship between Ba6Ti17O40 and TiO2 was found. Topotaxy is facilitated by a certain similarity in the oxygen sublattices of TiO2 and Ba6Ti17O40. The mechanism of the reaction occurring between BaO vapor and the TiO2 surface at high temperature is discussed. On the other hand, several well-oriented Ba4Ti13O30, Ba6Ti17O40 and Ba2Ti5O12 phases were observed to be embedded in the mainly forming Ba2TiSi2O8 phase after a solid–solid reaction of amorphous SiO2 thin films with (001) BaTiO3 substrates at temperatures above 1000 °C. They were formed by a topotaxial reaction involving the transformation of (111) planes of BaTiO3 into (001) planes of the Ti-rich phases by removal of BaO and insertion of TiO2. Cross-sections of the interfaces between the substrates and the various reaction products are studied by (high-resolution) transmission electron microscopy. |
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Keywords: | Ba6Ti17O40 Ba2Ti5O12 BaTiO3 TiO2 Solid state reactions Interfaces TEM Topotaxy |
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