Synthesis of layered transition-metal oxynitrides: search for novel oxynitride superconductors

目前的工作涉及在氮氧化物（一种混合阴离子的材料族）中寻找新的层状超导体。我们专注于Li-Nb氧氮化物，包含化学上不同的两种金属Li和Nb的层状排列。以LiNb3O8为原料，通过氨氮化反应合成了六方氮氧化物Li0.88Nb3.0(O0.13N0.87)4。x射线和中子衍射分析表明，该氮氧化物由不同Li/Nb比的八面体层和棱柱体层交替叠加而成：在八面体层中存在大量的Li和Nb原子（Li/Nb = 43/57），棱柱体位置优先被Nb占据（Li/Nb = 3/97）。在约3k处，电阻率突然下降。此外，在此温度以下观察到较大的抗磁性和比热异常，表明Li-Nb氧化氮中出现了超导性。

The present work dealt with search for novel layered superconductors among oxynitrides, a material family with mixed anions. We focused on Li-Nb oxynitrides, containing a layered arrangement of chemically distinct two metals of Li and Nb.A hexagonal oxynitride Li0.88Nb3.0(O0.13N0.87)4 was synthesized through ammonia nitridation of LiNb3O8. X-ray and neutron diffraction analyses 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.