Comprehensive Investigation of Anion Species in Crystalline Li + ion Conductor Li 27-x [P 4 O 7+x N 9-x ]O 3 (x≈1.9(3)).

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 I 4 ‾ 3 d ${I\overline 4 3d}$ 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.
(© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)