We demonstrate that (NH₄)₂Si_0.5Ti_0.5P₄O₁₃ is an excellent proton conductor. The crystallographic information concerning the hydrogen positions is unraveled from neutron-powder-diffraction (NPD) data for the first time. This study shows that all the hydrogen atoms are connected though H bonds, establishing a two-dimensional path between the [(Si_0.5Ti_0.5)P₄O₁₃^2–]_n layers for proton diffusion across the crystal structure by breaking and reconstructing intermediate H–O═P bonds. This transient species probably reduces the potential energy of the H jump from an ammonium unit to the next neighboring NH₄⁺ unit. Both theoretical and experimental results support an interstitial-proton-conduction mechanism. The proton conductivities of (NH₄)₂Si_0.5Ti_0.5P₄O₁₃ reach 0.0061 and 0.024 S cm^–1 in humid air at 125 and 250 °C, respectively. This finding demonstrates that (NH₄)₂Si_0.5Ti_0.5P₄O₁₃ is a promising electrolyte material operating at 150–250 °C. This work opens up a new avenue for designing and fabricating high-performance inorganic electrolytes.

中文翻译：

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质子在（NH ₄）₂ Si _0.5 Ti _0.5 P ₄ O _13中作为中温燃料电池的电解质的扩散途径的可视化

我们证明（NH ₄）₂ Si _0.5 Ti _0.5 P ₄ O ₁₃是一种优良的质子导体。首次从中子粉末衍射（NPD）数据中解开了有关氢位置的晶体学信息。这项研究表明，所有氢原子都通过H键相连，从而在[（Si _0.5 Ti _0.5）P ₄ O ₁₃ ^2– ] _n之间建立了二维路径。通过破坏和重建中间的H–O═P键，使质子在整个晶体结构中扩散。这种瞬态物质可能会降低H从铵单元跃迁至下一个相邻NH ₄ ⁺单元的势能。理论和实验结果均支持间隙质子传导机制。（NH ₄）₂ Si _0.5 Ti _0.5 P ₄ O ₁₃在125°C和250°C的潮湿空气中的质子电导率_分别达到0.0061和0.024 S cm ^–1。该发现表明（NH ₄）₂ Si _0.5 Ti _0.5 P₄ O ₁₃是一种有前途的电解质材料，可在150–250°C的温度下运行。这项工作为设计和制造高性能无机电解质开辟了一条新途径。