Partial nitrogen loss in SrTaO2N and LaTiO2N oxynitride perovskites

SrTaO2N heated in a helium atmosphere began to release nitrogen of approximately 30 at% at 950 degrees C while maintaining the perovskite structure and its color changed from orange to dark green. Then it decomposed above 1200 degrees 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 degrees C. After heating at 1500 degrees 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 degrees C changing its color from brown to black and then decomposed to a mixture of LaTiO3, La2O3, and TiN at 1100 degrees C. These temperatures are lower than those in SrTaO2N. (C) 2015 Elsevier Masson SAS. All rights reserved.