Lecture 20 Nonstoichiometric Defects

Lecture 20 Nonstoichiometric Defects - Non-Stoichimetric...

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Non-Stoichimetric defects Sources: Chemistry of Non-Stoichiometric Compounds, K. Kosuge, Oxford Science, 1994 Web page of Cava Lab, http://www.princeton.edu/~cavalab/tutorials/public/structures/ Waldner and Eriksson, Calphad Vol. 23, No. 2, pp. 189-218, 1999 www.uga.edu/caur/HREMWu.ppt The phase diagram of many oxides is exceedingly complicated.
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What is this due to? We need to step back a little to some inorganic chemistry concepts for oxides. Consider the simple example of SrTiO 3 , a perovskite. A “simple” way of looking at this is a ball and stick model: Here the Ti’s are red, the Oxygen light blue and the Sr dark blue. Unfortunately this is really a bit misleading. The Sr is really Sr 2+ and there are no real (or only very weak) covalent bonds between it and the oxygens, it is just ionic bonds. A slightly better representation would therefore be: Unfortunately this is really not that good. In reality the oxygen atoms are very “large”, almost touching, and what is important in the structure is non-bonded repulsions between them. We can draw this, but it is a bit of a mess:
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on is a polyhedral method. We represent the TiO
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This note was uploaded on 04/13/2010 for the course MAT SCI 404 taught by Professor Matsci during the Winter '10 term at Northwestern.

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Lecture 20 Nonstoichiometric Defects - Non-Stoichimetric...

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