  A hexagonal oxynitride (Li0.88_0.12)Nb3.0(O0.13N0.87)4 was synthesized
through ammonia nitridation of LiNb3O8. The structural analysis revealed that
this oxynitride consists of alternate stacking of octahedral and prismatic
layers with different Li/Nb ratios: significant amounts of Li and Nb atoms
(Li/Nb = 43/57) coexist in the octahedral layer, while the prismatic site is
preferentially occupied by Nb (Li/Nb = 3/97). A metallic behavior was
accompanied by an abrupt drop of electrical resistivity at about 3 K.
Furthermore, large diamagnetism and specific-heat anomaly were observed below
this temperature, suggesting the appearance of superconductivity in the Li-Nb
oxynitride.
