Microstructure, surface composition and chemical stability of partly ordered LaTiO 2N

Abstract

LaTiO 2N was synthesized in a thermal ammonolysis process of crystalline La 2Ti 2O 7 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 LaTiO 2N prepared from either precursor crystallizes in space group I 1 ¯ 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.