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The State of Trace Elements (In, Cu, Ag) in Sphalerite Studied by X-Ray Absorption Spectroscopy of Synthetic Minerals
Minerals ( IF 2.5 ) Pub Date : 2020-07-20 , DOI: 10.3390/min10070640
Nikolay D. Trofimov , Alexander L. Trigub , Boris R. Tagirov , Olga N. Filimonova , Polina V. Evstigneeva , Dmitriy A. Chareev , Kristina O. Kvashnina , Maximilian S. Nickolsky

The oxidation state and local atomic environment of admixtures of In, Cu, and Ag in synthetic sphalerite crystals were determined by X-ray absorption spectroscopy (XAS). The sphalerite crystals doped with In, Cu, Ag, In–Cu, and In–Ag were synthesized utilizing gas transport, salt flux, and dry synthesis techniques. Oxidation states of dopants were determined using X-ray absorption near edge structure (XANES) technique. The local atomic structure was studied by X-ray absorption fine structure spectroscopy (EXAFS). The spectra were recorded at Zn, In, Ag, and Cu K-edges. In all studied samples, In was in the 3+ oxidation state and replaced Zn in the structure of sphalerite, which occurs with the expansion of the nearest coordination shells due to the large In ionic radius. In the presence of In, the oxidation state of Cu and Ag is 1+, and both metals can form an isomorphous solid solution where they substitute for Zn according to the coupled substitution scheme 2Zn2+ ↔ Me+ + In3+. Moreover, Ag K-edges EXAFS spectra fitting, combined with the results obtained for In- and Au-bearing sphalerite shows that the Me-S distances in the first coordination shell in the solid solution state are correlated with the ionic radii and increase in the order of Cu < Ag < Au. The distortion of the atomic structure increases in the same order. The distant (second and third) coordination shells of Cu and Ag in sphalerite are split into two subshells, and the splitting is more pronounced for Ag. Analysis of the EXAFS spectra, coupled with the results of DFT (Density Function Theory) simulations, showed that the In–In and Me+–In3+ clustering is absent when the metals are present in the sphalerite solid solution. Therefore, all studied admixtures (In, Cu, Ag), as well as Au, are randomly distributed in the matrix of sphalerite, where the concentration of the elements in the “invisible” form can reach a few tens wt.%.

中文翻译:

用合成矿物的X射线吸收光谱研究方铅矿中微量元素(In,Cu,Ag)的状态

通过X射线吸收光谱法(XAS)测定了合成闪锌矿晶体中In,Cu和Ag的混合物的氧化态和局部原子环境。掺杂有In,Cu,Ag,In-Cu和In-Ag的闪锌矿晶体是利用气体传输,盐通量和干法合成技术合成的。使用X射线吸收近边缘结构(XANES)技术确定掺杂剂的氧化态。通过X射线吸收精细结构光谱学(EXAFS)研究了局部原子结构。光谱记录在Zn,In,Ag和Cu K处-边缘。在所有研究的样品中,In处于3+氧化态,并在闪锌矿结构中替代了Zn,这是由于In离子半径大而导致最近的配位壳膨胀而引起的。在In的存在下,Cu和Ag的氧化态为1+,并且两种金属都可以形成同晶型固溶体,并根据偶合取代方案2Zn 2+ + Me + + In 3+取代Zn 。此外,Ag K边缘EXAFS光谱拟合,再结合含In和Au的闪锌矿的结果,表明固溶态第一配位壳中的Me-S距离与离子半径相关,并按Cu <银<金 原子结构的变形以相同的顺序增加。闪锌矿中较远的(第二和第三)配位壳和Cu和Ag被分成两个子壳,而Ag的分裂更为明显。对EXAFS光谱的分析以及DFT(密度函数理论)模拟的结果表明,In-In和Me + -In 3+当闪锌矿固溶体中存在金属时,不会出现团簇。因此,所有研究的混合物(In,Cu,Ag)以及Au都随机分布在闪锌矿的基质中,其中“不可见”形式的元素浓度可达到几十重量%。
更新日期:2020-07-20
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