Comprehensive Investigation of Anion Species in Crystalline Li⁺ ion Conductor Li_27−x[P₄O_7+xN_9−x]O₃ (x≈1.9(3))

Abstract The Li + ion conductor Li 27− x [P 4 O 7+ x N 9− x ]O 3 ( x ≈1.9) has been synthesized from P 3 N 5 , Li 3 N and Li 2 O in a Ta ampoule at 800 °C under Ar atmosphere. The cubic compound crystallizes in space group with a =12.0106(14) Å and Z=4. It contains both non‐condensed [PO 2 N 2 ] 5− and [PO 3 N] 4− tetrahedra as well as O 2− ions, surrounded by Li + ions. Charge neutrality is achieved by partial occupancy of Li positions, which was refined with neutron powder diffraction data. Measurements of the partial ionic and electronic conductivity show a total ionic conductivity of 6.6×10 −8 S cm −1 with an activation energy of 0.46±0.02 eV and a bulk ionic conductivity of 4×10 −6 S cm −1 at 25 °C, which is close to the ionic conductivity of amorphous lithium nitridophosphate. This makes Li 27− x [P 4 O 7+ x N 9− x ]O 3 an interesting candidate for investigation of structural factors affecting ionic conductivity in lithium oxonitridophosphates.