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

本文的工作是在氮氧化物中寻找新型的层状超导体，氮氧化物是一种混合阴离子的材料。以LiNb 3 O 8为原料，采用氨氮化法合成了六方结构的氮氧化物Li 0. 88 Nb 3. 0（O 0. 13 N 0. 87）4。X射线和中子衍射分析表明，这种氮氧化物由具有不同Li/Nb比的八面体层和棱柱层的交替堆叠组成：大量的Li和Nb原子（Li/Nb = 43/57）共存于八面体层中，而棱柱位置优先被Nb占据（Li/Nb = 3/97）。在约3 K时，电阻率的突然下降伴随着金属行为.此外，在此温度以下观察到大的抗磁性和比热异常，这表明在Li-Nb氮氧化物中出现超导性。

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.