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首页> 外文OA文献 >A new formula and crystal structure for nickelskutterudite, (Ni,Co,Fe)As-3, and occupancy of the icosahedral cation site in the skutterudite group
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A new formula and crystal structure for nickelskutterudite, (Ni,Co,Fe)As-3, and occupancy of the icosahedral cation site in the skutterudite group

机译：镍方钴矿（Ni，Co，Fe）As-3的新分子式和晶体结构以及方钴矿群中二十面体阳离子位点的占有率

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摘要

We propose a new formula for the mineral nickelskutterudite, based on our observation that either (or both) Co or Fe3+ are essential structure constituents. The crystal structure of nickelskutterudite, (Ni,Co,Fe) As-3, cubic, Im (3) over bar, Z = 8: a = 8.2653(6) angstrom, V = 564.65(7) angstrom, has been refined to R-1 = 1.4% for 225 unique reflections I > 2 sigma(1) collected on a Bruker X8 four-circle diffractometer equipped with fine-focus, sealed tube MoKa radiation and an APEX-II CCD detector. This is the first report of the crystal structure of nickelskutterudite. Nickelskutterudite, a member of the skutterudite group of isostructural minerals, adopts a distorted perovskite structure with notably tilted octahedra and an unoccupied to partially occupied icosahedral metal site. In the structure of nickelskutterudite, there is one metal (B) site occupied by Ni, Co, or Fe in octahedral coordination with six As atoms. Procrystal electron density analysis shows each As anion is bonded to two cations and two As anions, resulting in a four-membered ring of bonded As with edges 2.547 and 2.475 angstrom. The extreme tilting of BAs6 octahedra is likely a consequence of the As-As bonding. The nickelskutterudite structure differs from the ideal perovskite structure (A(4)B(4)X(12)) in that As4 anion rings occupy three of the four icosahedral cages centered on the A sites. There are reported synthetic phases isomorphous with skutterudite with the other A site completely occupied by a cation (AB(4)X(12)). Electron microprobe analyses of nickelskutterudite gave an empirical chemical formula of (Ni0.62Co0.28Fe0.12)(Sigma 1.02)(AS(2.95)S(0.05))(Sigma 3.00) normalized to three anions. Pure NiAs3 nickelskutterudite, natural or synthesized, has not been reported. In nature, nickelskutterudite is always observed with significant Co and Fe, reportedly because all non-bonded valence electrons must be spin-paired. This suggests that nickelskutterudite must contain Co3+ and Fe2+, consistent with previous models since Ni4+ cannot spin-pair its seven non-bonded electrons, Co3+ and Fe2+, which can spin-pair all non-bonded electrons, are required to stabilize the structure. No anion deficiencies were found in the course of this study so, including the structurally necessary Co and Fe, the chemical formula of nickelskutterudite (currently given as NiAs3-x, by the IMA) should be considered (Ni,Co,Fe)As-3.
机译：根据我们的观察结果，我们提出了一种新的矿物镍方钴矿配方，其中Co（或Fe3 +）是（或两者都是）必不可少的结构成分。镍方钴矿（Ni，Co，Fe）As-3，立方，Im（3）在棒上的晶体结构，Z = 8：a = 8.2653（6）埃，V = 564.65（7）埃R-1 = 1.4％，用于在配备精细聚焦，密封管MoKa辐射和APEX-II CCD检测器的Bruker X8四圆衍射仪上收集的225个I> 2 sigma（1）的独特反射。这是镍方钴矿晶体结构的首次报道。镍skutterudite是同质结构矿物的skutterudite组的成员，采用畸变的钙钛矿结构，具有明显倾斜的八面体和未被占用的部分占据的二十面体金属位置。在镍方钴矿的结构中，有一个金属（B）位置被Ni，Co或Fe占据，并与六个As原子进行八面体配位。原晶电子密度分析显示，每个As阴离子均键合到两个阳离子和两个As阴离子上，从而形成键合As的四元环，其边缘为2.547和2.475埃。 BAs6八面体的极端倾斜可能是As-As键合的结果。镍方钴矿结构不同于理想的钙钛矿结构（A（4）B（4）X（12）），因为As4阴离子环占据了以A位点为中心的四个二十面体笼中的三个。据报道，合成相与方钴矿同构，另一个A位完全被阳离子（AB（4）X（12））占据。镍方钴矿的电子微探针分析给出了归一化为三个阴离子的（Ni0.62Co0.28Fe0.12）（Sigma 1.02）（AS（2.95）S（0.05））（Sigma 3.00）的经验化学式。天然或合成的纯NiAs3镍方钴矿尚未见报道。在自然界中，总是观察到镍方钴矿含大量的钴和铁，因为所有未键合的价电子必须成对配对。这表明镍方钴矿必须包含Co3 +和Fe2 +，这与以前的模型一致，因为Ni4 +无法对其七个非键合电子进行自旋配对，而Co3 +和Fe2 +可以使所有非键合电子自旋配对，这是稳定结构所必需的。在此研究过程中未发现任何阴离子缺陷，因此应考虑包括结构上必要的Co和Fe，镍方钴矿的化学分子式（IMA当前指定为NiAs3-x）（Ni，Co，Fe）As- 3。

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