新型中熵、高熵、低对称性钨酸盐的局域结构特性
Peculiarities of the local structure in new medium- and high-entropy, low-symmetry tungstates
摘要：
合成并表征了新的单斜（$P2$ / $c$）钨酸盐--中熵钨酸盐（Mn，Ni，Cu，Zn）WO $_4$和高熵钨酸盐（Mn，Co，Ni，Cu，Zn）WO $_4$。粉末X射线衍射和拉曼光谱证实了它们的相纯度和固溶体性质。X射线吸收光谱被用来探测金属阳离子周围的局部结构。基于理想固溶体模型的原子结构通过同时分析多个金属吸收边处的扩展X射线吸收精细结构光谱进行优化-（Mn，Ni，Cu，Zn）WO $_4$为五个，（Mn，Co，Ni，Cu，Zn）WO $_4$为六个-通过反向蒙特卡罗模拟。在这两种化合物中，Ni $^{2+}$离子具有最强的倾向，以组织其局部环境，并形成轻微扭曲的[NiO $_6$ ]八面体，而Mn $^{2+}$，Co $^{2+}$和Zn $^{2+}$离子具有强烈扭曲的八面体配位。最有趣的结果是在（Mn，Ni，Cu，Zn）WO $_4$和（Mn，Co，Ni，Cu，Zn）WO $_4$中[CuO $_6$ ]八面体的形状不同于在纯CuWO $_4$中发现的，其中存在强的Jahn-Teller畸变：[CuO $_6$ ]八面体随着稀释度的增加而变得更规则。
英文摘要：
New monoclinic ($P2$/$c$) tungstates - a medium-entropy tungstate, (Mn,Ni,Cu,Zn)WO$_4$, and a high-entropy tungstate, (Mn,Co,Ni,Cu,Zn)WO$_4$ - were synthesized and characterized. Their phase purity and solid solution nature were confirmed by powder X-ray diffraction and Raman spectroscopy. X-ray absorption spectroscopy was used to probe the local structure around metal cations. The atomic structures based on the ideal solid solution model were optimized by a simultaneous analysis of the extended X-ray absorption fine structure spectra at multiple metal absorption edges - five for (Mn,Ni,Cu,Zn)WO$_4$ and six for (Mn,Co,Ni,Cu,Zn)WO$_4$ - by means of reverse Monte Carlo simulations. In both compounds, Ni$^{2+}$ ions have the strongest tendency to organize their local environment and form slightly distorted [NiO$_6$] octahedra, whereas Mn$^{2+}$, Co$^{2+}$, and Zn$^{2+}$ ions have a strongly distorted octahedral coordination. The most intriguing result is that the shape of [CuO$_6$] octahedra in (Mn,Ni,Cu,Zn)WO$_4$ and (Mn,Co,Ni,Cu,Zn)WO$_4$ differs from that found in pure CuWO$_4$, where a strong Jahn-Teller distortion is present: [CuO$_6$] octahedra become more regular with increasing degree of dilution.
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