Preparation and thermal stability of oxynitride perovskite solid solution Sr1-xLaxTa1-xTixO2N

The thermal stability of oxynitride perovskites is very important for the fabrication of their dense ceramics. In this study, a solid solution of the oxynitride perovskite Sr1-xLaxTa1-xTixO2N was prepared via the ammonia nitridation of oxide precursors. The oxynitrides products obtained at x <= 0.2 and x >= 0.7 had tetragonal and triclinic perovskite-type structures, respectively. A neutron diffraction study on the oxynitride product obtained at x = 0.2 indicated that this tetragonal perovskite had a cis-type anion distribution similarly to SrTaO2N. The tetragonal perovskite released a part of nitrogen at approximately 1000 degrees C in a nitrogen atmosphere while maintaining the perovskite structure at least to 1450 degrees C. The oxynitride perovskites at x >= 0.5 gradually decomposed to a mixture of LaTiO2N, LaTiO3, La(OH)(3), La2O3, TiN and TaO above 1100 degrees C.