The Effect of Ga and Mo Doping on the Phase and Mobility of Interstitial Oxygen in K2ZnV2O7

The K 2 ZnV 2 O 7 material, as reported in our previous work, undergoes a phase transition from melilite-related structure to typical melilite structure upon Ga doping on the Zn site, with interstitial oxygen introduced and accompanied by an approximately two orders of magnitude ionic conductivity improvement (≈1.01 × 10 −1 S cm −1 at 600 °C for K 2 Zn 0.7 Ga 0.3 V 2 O 7.15 ). Herein, in order to further enhance the oxide-ion conduction by introducing more interstitial oxygen into the structure, a series of Ga and Mo codoped K 2 Zn 1- x Ga x V 2- y Mo y O 7+0.5 x +0.5 y (0 ≤ x ≤ 0.2, y = 0.1 and 0.2) materials are designed and synthesized via the traditional solid-state reaction method, with their phases and electrical properties being systematically studied. The results reveal that the Ga and Mo codoped materials retain the melilite-related structure and show a much lower conductivity, e.g., only ≈1.49 × 10 −2 S cm −1 at 600 °C for the composition of K 2 Zn 0.8 Ga 0.2 V 1.8 Mo 0.2 O 7.2 , despite its higher interstitial oxygen concentration compared to the single Ga-doped K 2 ZnV 2 O 7 (e.g., K 2 Zn 0.7 Ga 0.3 V 2 O 7.15 ). Therefore, the introduction of Mo into the structure appears to suppress the phase transition and decrease the mobility of interstitial oxygen for the K 2 ZnV 2 O 7 -based materials. These findings provide a more comprehensive perspective on the oxide-ion conduction optimization of melilite or melilite-related materials.