Synthesis, Structure, Solid‐State NMR Spectroscopy, and Electronic Structures of the Phosphidotrielates Li(3)AlP(2) and Li(3)GaP(2)

The lithium phosphidoaluminate Li(9)AlP(4) represents a promising new compound with a high lithium ion mobility. This triggered the search for new members in the family of lithium phosphidotrielates, and the novel compounds Li(3)AlP(2) and Li(3)GaP(2), obtained directly from the elements via ball milling and subsequent annealing, are reported here. It was unexpectedly found through band structure calculations that Li(3)AlP(2) and Li(3)GaP(2) are direct band gap semiconductors with band gaps of 3.1 and 2.8 eV, respectively. Rietveld analyses reveal that both compounds crystallize isotypically in the orthorhombic space group Cmce (no. 64) with lattice parameters of a=11.5138(2), b=11.7634(2) and c=5.8202(1) Å for Li(3)AlP(2), and a=11.5839(2), b=11.7809(2) and c=5.8129(2) Å for Li(3)GaP(2). The crystal structures feature TrP(4) (Tr=Al, Ga) corner‐ and edge‐sharing tetrahedra, forming two‐dimensional [Formula: see text] layers. The lithium atoms are located between and inside these layers. The crystal structures were confirmed by MAS‐NMR spectroscopy.