Magneli-type phases

Magneli-type TiH02H 1 phases should have been formed (Berger et al., 2001 Naumann et al., 2003). However, brookite formation may be the result of a thermodynamic process akin to Oswald s rule of steps, whereby the steep temperature gradient attained during plasma spraying will cause the formation of metastable phases. 

Kue] Kuehlewein, H., The Iron-Nickel-Cobalt Alloys (in German), Physikal. Z., 31, 626-640 (1930) (Experimental, Magn. Prop., Meehan. Prop., Phase Diagram, Phase Relations, 59) [193 IMas] Masumoto, H., On the Thermal Expansion of the Alloys of Iron, Nickel and Cobalt, and the Cause of the Small Expansibility of Alloys of the Invar Type , Sci. Rep. Tohoku Imp. Univ., 20, 101-123 (1931) (Experimental, Thermodyn., 27)... 

There are few oxides that - considering a given type - have ideal geometric structure. Besides, many oxide phases show deviation from the stoichiometry, or metal ions are in different oxidation states, e.g. in ordered phases (Magneli phases). A distortion of coordination polyhedra occurs in these oxides and as a result M-O bond lengths are differentiated. Hence, the volume of an unit cell is well defined, however, it is much more difficult to determine "real" ion positions and distances between them Besides, unit cells of oxides differing by structure and compxjsition contain different numbers of molecules, making the comparison of their volumes impossible. 

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