Synthesis, structure and electrical properties of N-doped Li3VO4

Abstract

N-doped Li₃VO₄ of general formula Li_3+xVO_4−xN_x was prepared by solid state reaction of Li₃N, V₂O₅ and either Li₂CO₃ or LiOH·H₂O. A solid solution based on the low temperature β polymorph of Li₃VO₄ was obtained with composition 0 ≤ x ≤ 0.2. Structural studies by X-ray and neutron powder diffraction confirmed the partial replacement of oxygen on the O(1) sites by N together with creation of an equal number of Li⁺ ions which are located off-centre in adjacent octahedral Li(3) sites. Electrical property measurements on sintered pellets using impedance spectroscopy showed that the solid solutions are modest conductors of Li⁺ ions, consistent with the partial occupancy of Li⁺ ions in the interstitial octahedral sites. The activation energy for conduction of samples prepared using LiOH·H₂O, ∼1.91 eV, is much greater than for samples prepared at higher temperature, using Li₂CO₃, ∼0.78 eV; it is speculated that this is due to ion trapping in Li_i˙/N₀′ defect clusters. This study represents a relatively new method for doping Li⁺ ions into a structure by aliovalent anion doping: partial replacement of O by N is compensated by creation of interstitial Li⁺ ions.