High conductivity and diffusion mechanism of oxide-ion in Sillén-Aurivillius phase oxobromide
Abstract
Oxide-ion conductors are applicable in fields such as solid oxide fuel cells (SOFC), oxygen sensors and exchange membranes. A pivotal factor in advancing these applications is the discovery of new classes of oxide-ion conductors. Mixed-anion compounds, with their diverse coordination environments and orbital interactions, offer opportunities to tailor functional properties. In this work, we report Sillén–Aurivillius phase oxyhalides Bi4MO8X (M = Nb5+, Ta5+; X = Cl-, Br-, I-) as a new family of oxide-ion conductors. Among them, Oxobromide Bi4TaO8Br exhibits the highest oxide-ion conductivity, attributed to its expanded lattice and favorable oxygen-vacancy migration pathways. Furthermore, Sr2+ substitution at the Bi3+ sites within the oxide-ion conducting layers significantly enhances ionic transport, with Bi3.9Sr0.1TaO7.95Br achieving a bulk conductivity of 5.3×10-2 S cm-1 at 700 ℃, surpassing commercial SOFC electrolytes such as yttria-stabilized zirconia (YSZ) and La0.8Sr0.2Ga0.83Mg0.17O2.815 (LSGM). This represents the first example of an oxide-ion-conducting oxobromide exhibiting such high oxide-ion conductivity. These findings not only establish a new class of oxide-ion conductors, but also highlight a promising design paradigm for enhancing ionic transport in mixed-anion oxyhalides through halide regulation and targeted doping.
