Microstructure, surface composition and chemical stability of partly ordered LaTiO2N

LaTiO2N was synthesized in a thermal ammonolysis process of crystalline La2Ti2O7 prepared by conventional solid state reaction or by ammonolysis of a homogeneous amorphous precursor obtained from a soft-chemistry approach. At room temperature slowly cooled LaTiO2N prepared from either precursor crystallizes in space group I (1) over bar and shows a partially ordered anionic arrangement in contrast to a quenched reference sample. The material possesses a complex microstructure represented by twin domains of different types and orientations, as well as incommensurately modulated fragments. The presence of minor C- and N-containing phases such as carbonates, cyanides and nitrates as well as a small amount of a reoxidation intermediate was detected by infrared and Raman spectroscopy. These small amounts of secondary phases can generally influence the results of the O/N content determination of oxynitride compounds when using thermal analysis methods. The formation of such unwanted secondary phases can be avoided by quenching the oxynitride sample or by cooling in inert atmosphere. (C) 2009 Elsevier Masson SAS. All rights reserved.