Synthesis, Crystal Structure and Optical Properties of LaNbON2

LaNbON2 was synthesized by thermal ammonolysis of crystalline LaNbO4 prepared by a soft chemistry approach. LaNbON2 crystallizes in a distorted GdFeO3-like perovskite structure with space group Pnma and a = 5.5720(2), b = 7.8656(4), c = 5.6066(3) angstrom and a random anionic arrangement as revealed by neutron diffraction. Elongated displacement ellipsoids found by neutron diffraction and a considerable deuce of residual bond strain as revealed by the bond valence calculations suggest a local positional disorder of the niobium ions. The material exhibits good chemical stability at ambient conditions and a considerable thermal stability upon heating in synthetic air (up to T = 500 K) as well as a small optical band gap of similar to 1.7 eV.