Phase evolution, electrical properties, and conductivity mechanism in LiNbWO6

Abstract

The tetragonal LiNbWO 6 (α−LiNbWO 6 ) with a trirutile structure was previously reported to have good lithium ion conductivity. However, the electrical properties of the hexagonal LiNbWO 6 (β−LiNbWO 6 hereafter) polymorph have not been reported yet mainly due to the difficulty to obtain single-phase. Herein, by quenching the sample from high temperature to room temperature at ambient air condition, a series of pure-phase β−LiNb 1- x Ta x WO 6 ( x = 0, 0.05, 0.1) materials were successfully prepared. The phase evolutions and conductivities of these materials were investigated by variable temperature X-ray diffraction and alternating current impedance spectroscopy techniques, respectively. The results revealed that lithium ion conduction also dominated in this hexagonal polymorph of LiNbWO 6 and an interesting great ionic conduction enhancement behavior was observed at a temperature region of 660-800 ºC due to the minor phase transition from hexagonal to tetragonal. In addition, the possible ionic conducting mechanisms in both the tetragonal and hexagonal LiNbWO 6 materials were studied by the bond-valence-based method for the first time. The results disclosed two-dimensional and three-dimensional lithium ion migration pathways for the tetragonal and hexagonal LiNbWO 6 , respectively. • Hexagonal LiNb 1-x Ta x WO 6 (0≤x≤0.1) was prepared through solid-state reaction. • Lithium ion conduction was identified in hexagonal LiNb 1-x Ta x WO 6 . • Phase evolutions of LiNb 1-x Ta x WO 6 were investigated by variable temperature XRD. • Great conduction increase at 650-800 ºC was due to a composite electrolyte effect. • Conducting mechanisms for both the tetragonal and hexagonal LiNbWO 6 was studied.