High-entropy oxide ceramics for detecting the ionic conductivity component in electron conductors

• A novel high-entropy oxide (La0.2Gd0.2Tm0.2Lu0.2Y0.2)3.12Ti0.88O6.44 was synthesized to isolate the ionic conductivity component in a predominantly hole-conducting Tb-based titanate. • The high-entropy analogue exhibited proton conductivity of ~7 × 10−6 S/cm at 600°C, confirmed by an isotope effect with D2O showing lower conductivity than H2O. • The parent Tb3.12Ti0.88O6.44 showed maximum hole conductivity of ~22 S/cm at 600°C, highlighting the challenge of separating ionic contributions in mixed conductors. • This work provides a strategy for detecting and quantifying ionic conductivity in electronic conductors, relevant for SOFC/SOEC materials development.