A new lithium-containing phosphate, LiMg 3 (PO 4 )P 2 O 7 , was prepared by a solid-state reaction, and it was characterized by an ab initio structure determination method on the basis of synchrotron powder X-ray diffraction data. LiMg 3 (PO 4 )P 2 O 7 was found to be orthorhombic (space group Pnma) with lattice parameters a = 9.0387(1) Å, b = 10.6072 (1) Å, c = 8.3065(1) Å, and V = 796.39(1) Å 3 . The structure features infinite [Mg 3 O 10 ] ∞ layers that are parallel to the bc plane and that are interconnected along the a axis by PO 4 and P 2 O 7 groups. The [Mg 3 O 10 ] ∞ layer contains Mg 3 O 14 trimers that are formed by three edge-shared MgO 6 octahedra. The PO 4 and P 2 O 7 groups are located alternatingly between [Mg 3 O 10 ] ∞ layers. This gives rise to a three-dimensional framework that contains large tunnels along the directions [100] and [010]; the Li + ions are stabilized in these tunnels. AC impedance spectroscopy shows that LiMg 3 (PO 4 )P 2 O 7 has an ionic conductivity of 3.40 × 10 −5 S cm -1 at 769 K, with an activation energy of 1.17 eV.

Crystal Structure and Ion Conductivity of a New Mixed-Anion Phosphate LiMg 3(PO4)P2O7. -LiMg3(PO4)P2O7 is prepared by solid-state reaction of a 1:3:3 molar mixture of Li 2CO3, MgO, and (NH4)2HPO4 (1. 773 K, 8 h, 2. 973 K, 12 h). The material crystallizes in the orthorhombic space group Pnma (Z = 4, synchrotron powder XRD) and features infinite  2 [Mg3O10] layers which are interconnected by PO4 and P2O7 groups. The layers contain Mg 3O14 trimers formed by 3 edge-sharing MgO6 octahedra. Tunnels are formed along [100] and [010] which are stabilized by Li + ions. AC impedance spectroscopy shows an ionic conductivity of 3.40 x 10 -5 S/cm at 769 K with an activation energy of 1.17 eV. -(KIM, S.-C.; LEE, M.-S.; KANG, J.; KIM, Y.-I.; KIM*, S.-J.; J. Solid State Chem. 225 (2015) 335-339, http://dx.