Partial nitrogen loss in SrTaO2N and LaTiO2N oxynitride perovskites

•Thermal behavior was studied on SrTaO2N and LaTiO2N oxynitrides in helium flow.•Partially nitrogen lost perovskites were found during their decomposition.•Crystal structure and electrical property were studied on the SrTaO2N0.7 intermediate.•Cis-configuration was found in the TiO4N2 octahedron of LaTiO2N.

SrTaO2N heated in a helium atmosphere began to release nitrogen of approximately 30 at% at 950 °C while maintaining the perovskite structure and its color changed from orange to dark green. Then it decomposed above 1200 °C to a black mixture of Sr1.4Ta0.6O2.73, Ta2N, and Sr5Ta4O15. The second decomposition was not clearly observed when SrTaO2N was heated in a nitrogen atmosphere below 1550 °C. After heating at 1500 °C for 3 h under a 0.2 MPa nitrogen atmosphere, the perovskite product became dark green and conductive. Structure refinement results suggested that the product was a mixture of tetragonal and cubic perovskites with a decreased ordering of N3−/O2−. The sintered body was changed to an n-type semiconductor after a partial loss of nitrogen to be reduced from the originally insulating SrTaO2N perovskite lattice. LaTiO2N was confirmed to have a similar cis-configuration of the TiO4N2 octahedron as that of TaO4N2 in SrTaO2N. It also released some of its nitrogen at 800 °C changing its color from brown to black and then decomposed to a mixture of LaTiO3, La2O3, and TiN at 1100 °C. These temperatures are lower than those in SrTaO2N.

Graphical abstractOrange SrTaO2N and dark green SrTaO2N0.7 powder samples.Figure optionsDownload full-size imageDownload as PowerPoint slide