Crystal structure refinements of stoichiometric Ni₃Se₂ and NiSe

Abstract

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) Å, Z = 3] and NiSe [hexagonal, space group P63/mmc, a = 3.66147 (10), c = 5.35766 (16) Å, 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 > 4σ(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, θD, 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.

Crystal structures of rhodium-containing erlichmanite–laurite solid solutions (Os1–x–yRuxRhyS2: x = 0.09–0.60, y = 0.07–0.10) with unique compositional dependence

“…Laurite–erlichmanite minerals form at a very high temperature (～1250°C; Brenan and Andrews, 2001). Our synthetic experiments without flux under vacuum conditions (Unoki et al , 2021; Yoshiasa et al , 2021) indicated that RuS 2 and RuSe 2 crystals did not melt nor grow, even at 1300°C.…”

Kvačekite, NiSbSe, a new selenide mineral from Bukov, Czech Republic

“…This is slightly longer than observed Ni-Se and Ni-Sb distances of 2.469(3) and 2.579(3) Å, respectively. Considering Ni-Se distances, slightly longer NiSe separations of 2.503 Å were observed in synthetic NiSe (Unoki et al, 2021), an analogue of sederholmite, which adopts a nickeline-type structure. Ullmanite shows a Ni-Sb distance of 2.563 Å (Foecker and Jeitschko, 2001) which can be compared with the Ni-Sb separations in the kvačekite structure (2.579(3) Å).…”