While lithium phosphides have been investigated intensively, very little is known about the corresponding sodium-based phosphides. Here, we report on the first ternary Na–Ta–P compound Na₇TaP₄, which is easily accessible via ball milling of the elements and subsequent annealing. The single crystal X-ray structure determination [monoclinic symmetry; space group P2₁/c; and lattice parameters a = 11.5604(4), b = 8.1530(3), c = 11.5450(5) Å, and β = 101.602(3)°] reveals [TaP₄]^7– tetrahedra, which are surrounded by Na⁺ counterions. Na₇TaP₄ crystallizes in a new structure type. The structure can be described as a strongly distorted hexagonal close packing of P atoms, in which the Ta atoms are located in tetrahedral voids, and Na atoms occupy all octahedral voids and additionally 3/8 of the tetrahedral voids. The possibility to increase the ion conductivity by changing the number of charge carriers through aliovalent substitution in compounds containing [SiP₄]^8– and [AlP₄]^9– is considered. The ³¹P and ²³Na MAS NMR as well as the Raman spectra are in accordance with the structure model, and band structure calculations predict a direct band gap of 2.9 eV.

中文翻译：

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Na ₇ TaP ₄：含有[TaP ₄ ] ^7–四面体的三膦磷酸钠

尽管已对磷化锂进行了深入研究，但对相应的钠基磷化物知之甚少。在这里，我们报告了第一个三元Na-Ta-P化合物Na ₇ TaP ₄，可以通过元素的球磨和随后的退火轻松地获得。单晶X射线结构测定[单斜对称；空间群P 2 ₁ / c ; 晶格参数a = 11.5604（4），b = 8.1530（3），c = 11.5450（5）Å和β= 101.602（3）°]揭示了[TaP ₄ ] ^7–四面体，被Na ⁺抗衡离子包围。钠₇TaP ₄结晶成新的结构类型。该结构可以描述为P原子的高度扭曲的六角形紧密堆积，其中Ta原子位于四面体空隙中，而Na原子占据所有八面体空隙，并占据了所有四面体空隙的3/8。考虑了通过包含[SiP ₄ ] ^8–和[AlP ₄ ] ^9–的化合物通过异价取代来改变电荷载流子数量来增加离子电导率的可能性。的³¹ P和²³的Na MAS NMR以及拉曼光谱是根据结构模型，和带结构的计算预测为2.9eV的直接带隙。