Fujii Susumu, Gao Shenghan, Tassel Cédric, Zhu Tong, Broux Thibault, Okada Koji, Miyahara Yuto, Kuwabara Akihide, Kageyama Hiroshi
Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587, Japan.
Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan.
J Am Chem Soc. 2021 Jul 21;143(28):10668-10675. doi: 10.1021/jacs.1c04260. Epub 2021 Jul 6.
To improve ionic conductivity, solid-state electrolytes with polarizable anions that weakly interact with mobile ions have received much attention, a recent example being lithium/sodium-rich antiperovskite MHCh (M = Li, Na; Ch = S, Se, Te). Herein, in order to clarify the role of anions in antiperovskites, the MFCh family, in which the polarizable H anion at the octahedral center is replaced by the ionic F anion, is investigated theoretically and experimentally. We unexpectedly found that the stronger attractive interaction between F and M ions does not slow down the M ion diffusion, with the calculated energy barrier being as low as that of MHCh. This fact suggests that the low-frequency rotational phonon modes of the octahedron of cubic MFCh (and MHCh) are intrinsic to facilitate the fast ionic diffusion. A systematic analysis further reveals a correlation between the tolerance factor and the ionic transport: as decreases within the cubic phase, the rotational mode becomes softer, resulting in the reduction of the migration energy. The cubic iodine-doped LiFSe has a room-temperature ionic conductivity of 5 × 10 S/cm with a bulk activation energy of 0.18 eV.
为了提高离子电导率，具有与移动离子弱相互作用的可极化阴离子的固态电解质受到了广泛关注，最近的一个例子是富锂/钠反钙钛矿MHCh（M = Li，Na；Ch = S，Se，Te）。在此，为了阐明阴离子在反钙钛矿中的作用，理论和实验研究了MFCh家族，其中八面体中心的可极化H阴离子被离子性F阴离子取代。我们意外地发现，F与M离子之间更强的吸引相互作用并没有减缓M离子的扩散，计算出的能垒与MHCh一样低。这一事实表明，立方MFCh（和MHCh）八面体的低频旋转声子模式是促进快速离子扩散的内在因素。系统分析进一步揭示了容忍因子与离子传输之间的相关性：随着立方相内容忍因子的降低，旋转模式变得更软，导致迁移能降低。立方碘掺杂的LiFSe在室温下的离子电导率为5×10 S/cm，体活化能为0.18 eV。
