Na₃[Ti₂P₂O₁₀F]:  A New Oxyfluorinated Titanium Phosphate with an Ionic Conductive Property

Abstract

Titanium phosphate, Na 3 [Ti 2 P 2 O 10 F]· x H 2 O ( 1 ), has been synthesized under hydrothermal conditions and structurally characterized using powder X-ray diffraction, neutron diffraction, and selected area electron diffraction (SAED). 1 crystallizes in the tetragonal space group I 4/ mmm with a = 6.4207(1) Å and c = 10.6762(2) Å and can be described by the stacking of a square-net sheet consisting of alternative linkage of TiFO 5 octahedra and PO 4 tetrahedra. The TiFO 5 octahedron is highly distorted, with a short “titanyl” Ti−O bond and a long Ti−F bond. The “titanyl” oxygen is almost doubly bonded to Ti; the square-net sheets are linked only by sharing common F atoms, which lead to a rather opened framework containing 2D channels in the ab plane. The counter cations Na + and water molecules reside in the channels. At high temperature, the adsorbed water molecules escape from the channels, leading to an anhydrous phase Na 3 [Ti 2 P 2 O 10 F] ( 2 ) with exactly the same structural framework as that of 1 . 2 is stable at high temperature in an Ar atmosphere, but decomposes to other known titanium phosphates and oxide at about 650 °C in air. The Na ions in the compound are exchangeable. In addition, 2 exhibits a Na conductivity comparable to that of the NASICON type titanium phosphates (1.0 × 10 - 4 Ω - 1 cm - 1 at 200 °C).