Phases, stabilities, and oxide ion conductions of multiple lanthanide and tungsten co–doped δ-Bi2O3-based materials: From low to high configuration entropy

Abstract

In this work, a series of multiple lanthanide and tungsten co-doped fluorite structured (Bi2O3)0.95-x(Ho0.4Er0.4Tm0.4Yb0.4Lu0.4O3)x(WO3)0.05 (x = 0.1, 0.2, 0.3, 0.4) and (Bi2O3)0.26(Ho0.5Er0.5Tm0.5Yb0.5O3)0.48(WO3)0.26 materials were prepared by traditional solid-state reaction method. The phases, stabilities, and electrical properties of these materials were thoroughly studied. The results revealed that under high oxygen partial pressure, CO2, or inert atmospheres, all these samples had excellent long term thermal stability and chemical stability, and the samples of (Bi2O3)0.95-x(Ho0.4Er0.4Tm0.4Yb0.4Lu0.4O3)x(WO3)0.05 (x = 0.1, 0.2, 0.3, 0.4) with low or mediate configuration entropies showed pure and high oxide ion conductivities, e.g. ∼2.6 × 10−2 S/cm at 600 °C for the sample x = 0.2. Whereas, for the (Bi2O3)0.26(Ho0.5Er0.5Tm0.5Yb0.5O3)0.48(WO3)0.26 sample with high configuration entropy, pure ionic conduction occurred only within a narrow temperature range (700−750 °C) under the N2 atmosphere. Under strong reducing condition, only the high-entropy sample (Bi2O3)0.26(Ho0.5Er0.5Tm0.5Yb0.5O3)0.48(WO3)0.26 showed high phase and chemical stabilities, but would introduce strong electronic conduction rise from the reduction of the high content W6+. While for (Bi2O3)0.95-x(Ho0.4Er0.4Tm0.4Yb0.4Lu0.4O3)x(WO3)0.05 with low or mediate configuration, phase decompositions with impurities of Bi metal and HoH2 were observed under strong reducing atmosphere, accompany with obviously decreased conductivities. Therefore, we provided here a comprehensive understanding for the multiple components doped Bi2O3-based materials with configuration entropy from low to high on their phases, stabilities, and electrical properties, and suggested a new strategy for designing and stabilizing bismuth-oxide-based materials.