Phosphide-based materials have been investigated as promising candidates for solid electrolytes, among which the recently reported Li9AlP4 displays an ionic conductivity of 3 mS∙cm−1. While the phases Li-Al-P and Li-Ga-P...

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Recently, ternary lithium phosphides have been studied intensively owing to their high lithium ion conductivities. Much less is known about the corresponding sodium-containing compounds, and during investigations aiming for sodium phosphidotrielates, two new compounds have been obtained. The sodium phosphidoaluminumtantalate Na 10 AlTaP 6 , at first obtained as a by-product from the reaction with the container material, crystallizes in the monoclinic space group P2 1 /n (no. 14) with lattice parameters of a = 8.0790(3) Å, b = 7.3489(2) Å, c = 13.2054(4) Å, and β = 90.773(2)°. The crystal structure contains dimers of edge-sharing [(Al 0.5 Ta 0.5 )P 4 ] tetrahedra with a mixed Al/Ta site. DFT calculations support the presence of this type of arrangement instead of homonuclear Al 2 P 6 or Ta 2 P 6 dimers. The 31 P and 23 Na MAS NMR as well as the Raman spectra confirm the structure model. The assignment of the chemical shifts is confirmed applying the DFT-PBE method on the basis of the ordered structural model with mixed AlTaP 6 dimers. The sodium phosphidogallate Na 3 GaP 2 crystallizes in the orthorhombic space group Ibam (no. 72) with lattice parameters of a = 13.081(3) Å, b = 6.728(1) Å, and c = 6.211(1) Å and is isotypic to Na 3 AlP 2 . Na 3 GaP 2 exhibits linear chains of edge-sharing 1 1 [GaP 4/2 ] tetrahedra. For both compounds band structure calculations predict indirect band gaps of 2.9 eV.

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