LiTa2PO8: a fast lithium-ion conductor with new framework structure

Abstract

A new lithium-ion conducting oxide, LiTa₂PO₈, with a three-dimensional (3D) framework structure was synthesized. The complementary use of synchrotron XRD and neutron diffraction revealed that LiTa₂PO₈ crystallized into a monoclinic system (space group C2/c) with lattice parameters a ≈ 9.716 Å, b ≈ 11.536 Å, c ≈ 10.697 Å, and β = 90.04°. In this structure, the TaO₆ octahedra and PO₄ tetrahedra are connected via corner-sharing to form an unprecedented anionic framework, [(TaO_6/2)₂(PO_4/2)]⁻, providing a 3D pathway for lithium-ion conduction. The sintered LiTa₂PO₈ pellets exhibited excellent lithium-ion conductivities: bulk conductivity of 1.6 × 10⁻³ S cm⁻¹ and total conductivity of 2.5 × 10⁻⁴ S cm⁻¹ at 25 °C.