LiTa2PO8: a fast lithium-ion conductor with new framework structure†
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, [(TaO6/2)2(PO4/2)]−, 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.