Role of Na+ Interstitials and Dopants in Enhancing the Na+ Conductivity of the Cubic Na3PS4 Superionic Conductor

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• 作者：Zhuoying Zhu ; Iek-Heng Chu ; Zhi Deng ; Shyue Ping Ong
• 刊名：Chemistry of Materials
• 出版年：2015
• 出版时间：December 22, 2015
• 年：2015
• 卷：27
• 期：24
• 页码：8318-8325
• 全文大小：473K
• ISSN：1520-5002

文摘

In this work, we performed a first-principles investigation of the phase stability, dopant formation energy and Na⁺ conductivity of pristine and doped cubic Na₃PS₄ (c-Na₃PS₄). We show that pristine c-Na₃PS₄ is an extremely poor Na ionic conductor, and the introduction of Na⁺ excess is the key to achieving reasonable Na⁺ conductivities. We studied the effect of aliovalent doping of M⁴⁺ for P⁵⁺ in c-Na₃PS₄, yielding Na_3+xM_xP_1鈥?i>xS₄ (M = Si, Ge, and Sn with x = 0.0625; M = Si with x = 0.125). The formation energies in all the doped structures with dopant concentration of x = 0.0625 are found to be relatively low. Using ab initio molecular dynamics simulations, we predict that 6.25% Si-doped c-Na₃PS₄ has a Na⁺ conductivity of 1.66 mS/cm, in excellent agreement with previous experimental results. Remarkably, we find that Sn⁴⁺ doping at the same concentration yields a much higher predicted Na⁺ conductivity of 10.7 mS/cm, though with a higher dopant formation energy. A higher Si⁴⁺ doping concentration of x = 0.125 also yields a significant increase in Na⁺ conductivity with an even higher dopant formation energy. Finally, topological and van Hove correlation function analyses suggest that the channel volume and correlation in Na⁺ motions may play important roles in enhancing Na⁺ conductivity in this structure.