Niwa Ken, Terabe Toshiki, Kato Daiki, Takayama Shin, Kato Masahiko, Soda Kazuo, Hasegawa Masashi
Department of Crystalline Materials Science, ‡Department of Quantum Engineering, Graduate School of Engineering, and §Nagoya Synchrotron Radiation Center, Nagoya University , Nagoya, Japan.
Inorg Chem. 2017 Jun 5;56(11):6410-6418. doi: 10.1021/acs.inorgchem.7b00516. Epub 2017 May 16.
Highly coordinated iron and cobalt nitrides were successfully synthesized via direct chemical reaction between a transition metal and molecular nitrogen at pressures above approximately 30 GPa using a laser-heated diamond anvil cell. The synthesized novel transition metal nitrides were found to crystallize into the NiAs-type or marcasite-type structure. NiAs-type FeN could be quenched at ambient pressure, although it was gradually converted to the ZnS-type structure after the pressure was released. On the other hand, CoN was recovered with ZnS-type structure through a phase transition from NiAs-type structure at approximately a few gigapascals during decompression. Marcasite-type CoN was also synthesized at pressures above approximately 30 GPa. High-pressure in situ X-ray diffraction measurement showed that the zero-pressure bulk modulus of marcasite-type CoN is 216(18) GPa, which is comparable to that of RhN. This indicates that the interatomic distance of the N-N dimer in marcasite-type CoN is short because of weak orbital interaction between cobalt and nitrogen atoms, as in RhN. Surprisingly, a first-principles electronic band calculation suggests that the NiAs-type FeN and CoN and marcasite-type CoN exhibit metallic characteristics with magnetic moments of 3.4, 0.6, and 1.2 μ, respectively. The ferromagnetic NiAs-type structure originates from the anisotropic arrangement of transition atoms stacked along the c axis.
利用激光加热金刚石对顶砧，通过过渡金属与分子氮在约30 GPa以上压力下的直接化学反应，成功合成了高度配位的铁和钴氮化物。发现合成的新型过渡金属氮化物结晶为NiAs型或白铁矿型结构。NiAs型FeN在常压下可以淬火，尽管在压力释放后它会逐渐转变为ZnS型结构。另一方面，CoN在减压过程中大约几个吉帕斯卡时通过从NiAs型结构的相变恢复为ZnS型结构。白铁矿型CoN也在约30 GPa以上的压力下合成。高压原位X射线衍射测量表明，白铁矿型CoN的零压体积模量为216(18) GPa，与RhN相当。这表明白铁矿型CoN中N-N二聚体的原子间距离较短，这是由于钴和氮原子之间的轨道相互作用较弱，与RhN情况相同。令人惊讶的是，第一性原理电子能带计算表明，NiAs型FeN和CoN以及白铁矿型CoN分别表现出具有3.4、0.6和1.2 μ磁矩的金属特性。铁磁性NiAs型结构源于沿c轴堆叠的过渡原子的各向异性排列。
