Exploring the stability and protonic conductivity in W- and Mo-substituted LaNbO4 under a reducing atmosphere

Abstract

LaNb_0.84W_0.16O_4+δ (LNW16) and LaNb_0.84Mo_0.16O_4+δ (LNM16) have been synthesized via a solid-state reaction route. Both samples underwent 5%-H₂ treatments at 800 °C to investigate their stability under a reducing atmosphere. The crystal structures, compositions, and oxidation states were studied before and after treatment showing excellent structural, compositional and redox stability of LaNb_0.84W_0.16O_4+δ, while LaNb_0.84Mo_0.16O_4+δ is reduced significantly. Therefore, the electrochemical performance of LaNb_0.84W_0.16O_4+δ under reducing atmospheres was further investigated. Higher conductivity was observed for the LNW16 samples measured under reducing atmospheres. However, the larger conductivity enhancement in the low temperature range (400 °C to 600 °C) compared with the high temperature range (600 °C to 800 °C) deviated from the conventional electronic conductivity emerging from reduction. DC polarization measurements further proved the predominant protonic conductivity in LaNb_0.84W_0.16O_4+δ under reducing atmospheres.