Crystal structure refinements of stoichiometric Ni3Se2 and NiSe
Crystal structure refinements of stoichiometric Ni3Se2 and NiSe
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DOI：
10.1107/s2053229621002187
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发表时间：
2021-04-01
影响因子：
0.8
通讯作者：
Nakatsuka, Akihiko
中科院分区：
文献类型：
--
作者：
Unoki, Kohei;Yoshiasa, Akira;Nakatsuka, Akihiko
具有化学计量化学成分的 Ni3Se2（二硒化三镍）和 NiSe（硒化镍）单晶在真空石英玻璃管中生长。通过扫描电子显微镜和能量色散X射线光谱（SEM/EDS）测定了Ni3Se2和NiSe单晶的化学成分。 Ni3Se2 [菱面体，空间群 R32，a = 6.02813 (13)，c = 7.24883 (16) 埃，Z = 3] 和 NiSe [六方晶系，空间群 P6(3)/mmc，a = 3.66147 (10)，c = 5.35766 (16) 埃，Z = [2] 通过单晶 X 射线衍射进行分析，并精炼得到 117 次和 85 次独特反射的 R 值分别为 0.020 和 0.018，且 F-o > 4 sigma(F-o)。 R32是可以存在对映体结构的Sohncke型空间群；通过Flack参数-0.05(2)确认细化获得的单域结构是正确的。除了 Ni-Se 键之外，两种化合物中还存在 Ni-Ni 键。 NiSe中各原子的原子位移参数（均方位移）值比Ni3Se2大。 NiSe 中原子的较大振幅对应于 NiSe 中比 Ni3Se2 中更长的 Ni-Se 和 Ni-Ni 键长。根据 Ni3Se2 中 Ni 和 Se 的观测均方位移估计的德拜温度 θ(D) 分别为 322 和 298 K，而 NiSe 中 Ni 和 Se 的德拜温度分别为 246 和 241 K。结构中大空腔的存在和弱结合力可能是造成 NiSe 晶体脆性和软性的原因。
Single crystals of Ni3Se2 (trinickel diselenide) and NiSe (nickel selenide) with stoichiometric chemical compositions were grown in evacuated silica-glass tubes. The chemical compositions of the single crystals of Ni3Se2 and NiSe were determined by scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS). The crystal structures of Ni3Se2 [rhombohedral, space group R32, a = 6.02813 (13), c = 7.24883 (16) angstrom, Z = 3] and NiSe [hexagonal, space group P6(3)/mmc, a = 3.66147 (10), c = 5.35766 (16) angstrom, Z = 2] were analyzed by single-crystal X-ray diffraction and refined to yield R values of 0.020 and 0.018 for 117 and 85 unique reflections, respectively, with F-o > 4 sigma(F-o). R32 is a Sohncke type of space group where enantiomeric structures can exist; the single-domain structure obtained by the refinement was confirmed to be correct by a Flack parameter of -0.05 (2). The existence of Ni-Ni bonds was confirmed in both compounds, in addition to the Ni-Se bonds. The value of the atomic displacement parameter (mean-square displacement) of each atom in NiSe was larger than that in Ni3Se2. The larger amplitude of the atoms in NiSe corresponds to longer Ni-Se and Ni-Ni bond lengths in NiSe than in Ni3Se2. The Debye temperatures, theta(D), estimated from observed mean-square displacements for Ni and Se in Ni3Se2, were 322 and 298 K, respectively, while those for Ni and Se in NiSe were 246 and 241 K, respectively. The existence of large cavities in the structure and the weak bonding force are likely responsible for the brittle and soft nature of the NiSe crystal.