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Electronic structure and sodium-ion diffusion in glaserite-type A3−хNa1+х(MoO4)2 (A = Cs, K) studied with first-principles calculations
Solid State Ionics ( IF 3.0 ) Pub Date : 2020-10-19 , DOI: 10.1016/j.ssi.2020.115484
A.V. Serdtsev , D.V. Suetin , S.F. Solodovnikov , O.A. Gulyaeva , N.I. Medvedeva

Here we present an ab initio insight into the electronic structure and sodium diffusion in A3−хNa1+х(MoO4)2 with trigonal (A = Cs) and monoclinic (A = K) glaserite-type structures. Our DFT calculations predict the stability of К3−xNa1+x(МoO4)2 to high sodium content and a significantly smaller homogeneity region for Cs3−xNa1+x(МoO4)2 in accordance with experimental findings. These molybdates are wide-gap insulators with a band gap of 4.2 eV, which is very weakly dependent on the sodium content. The calculated electric field gradients at the Na and A sites were related to the anisotropy of electronic charge distribution and used to predict the quadrupole frequencies of the 133Cs, 39K and 23Na NMR lines in Cs3−хNa1+х(MoO4)2 and K3−хNa1+х(MoO4)2. We examined the possible diffusion paths of Na+ ions and showed that the direct Na−Na migration is unlikely due to a large energy barrier in both molybdates. Instead, the Na+ ions can migrate through the A positions with much lower barriers in A3−xNa1+x(МoO4)2. Therefore, designing stable non-stoichiometric compositions may be a way to reach good sodium-ion diffusion in double molybdates with the glaserite-type structure.



中文翻译:

在芒硝型电子结构和钠离子扩散3- х的Na 1+ х氧化钼(MoO 42 = CS,K)与第一原理计算研究

这里,我们提出一个从头洞察的电子结构和钠扩散3- х的Na 1+ х氧化钼(MoO 42与三角( = Cs)的和单斜( = K)芒硝型结构。我们的DFT计算预测К的稳定性3- X的Na 1+ X(МoO 42至钠含量高和Cs的一个显著较小均匀性区域3- X的Na 1+ X(МoO 42根据实验结果。这些钼酸盐是带隙为4.2 eV的宽带隙绝缘体,其对钠含量的依赖性非常弱。在Na和所计算出的电场梯度位点相关的电子电荷分布的各向异性和用于预测的四极频率133个CS,39 K和23条的Na NMR线Cs的3- х的Na 1+ х(的MoO 42和K 3- х的Na 1+ х氧化钼(MoO 42。我们研究了Na +可能的扩散路径离子,并表明由于两种钼酸盐中的能量垒较大,直接Na-Na迁移不太可能。取而代之的是,钠+离子可通过迁移以低得多的屏障位置3- X的Na 1+ X(МoO 42。因此,设计稳定的非化学计量组成可能是在具有玻璃石型结构的双钼酸盐中达到良好的钠离子扩散的方法。

更新日期:2020-10-30
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