First Ternary Sodium Phosphidotantalate

First Ternary Sodium Phosphidotantalate


Phosphide-based lithium-ion conductors with potential uses in batteries have been well studied. In contrast, little is known about the corresponding sodium phosphide compounds and their sodium-ion conductivity.

Thomas F. Fässler, Technical University of Munich, Garching, Germany, and colleagues have synthesized the first ternary Na–Ta–P compound, the sodium phosphidotantalate Na7TaP4. The team originally wanted to prepare a sodium analogue of the lithium-ion conductor Li9AlP4 by reacting the elements Na, Al, and P in tantalum ampules. Instead, they obtained Na7TaP4. They then developed a more efficient synthesis of this new compound, where Na7TaP4 is prepared from the elements via ball milling and subsequent annealing at up to up to 973 K (ca. 700 °C).

Na7TaP4 was characterized using X-ray diffraction. The compound crystallizes in a new structure type in the monoclinic space group P21/c. The structure (pictured) contains isolated [TaP4]7– tetrahedra—a rarely found structural motif—surrounded by sodium atoms.



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