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

In this work, a series of multiple lanthanide and tungsten co-doped fluorite structured (Bi 2 O 3 ) 0.95- x (Ho 0.4 Er 0.4 Tm 0.4 Yb 0.4 Lu 0.4 O 3 ) x (WO 3 ) 0.05 ( x  = 0.1, 0.2, 0.3, 0.4) and (Bi 2 O 3 ) 0.26 (Ho 0.5 Er 0.5 Tm 0.5 Yb 0.5 O 3 ) 0.48 (WO 3 ) 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, CO 2 , or inert atmospheres, all these samples had excellent long term thermal stability and chemical stability, and the samples of (Bi 2 O 3 ) 0.95- x (Ho 0.4 Er 0.4 Tm 0.4 Yb 0.4 Lu 0.4 O 3 ) x (WO 3 ) 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 (Bi 2 O 3 ) 0.26 (Ho 0.5 Er 0.5 Tm 0.5 Yb 0.5 O 3 ) 0.48 (WO 3 ) 0.26 sample with high configuration entropy, pure ionic conduction occurred only within a narrow temperature range (700−750 °C) under the N 2 atmosphere. Under strong reducing condition, only the high-entropy sample (Bi 2 O 3 ) 0.26 (Ho 0.5 Er 0.5 Tm 0.5 Yb 0.5 O 3 ) 0.48 (WO 3 ) 0.26 showed high phase and chemical stabilities, but would introduce strong electronic conduction rise from the reduction of the high content W 6+ . While for (Bi 2 O 3 ) 0.95- x (Ho 0.4 Er 0.4 Tm 0.4 Yb 0.4 Lu 0.4 O 3 ) x (WO 3 ) 0.05 with low or mediate configuration, phase decompositions with impurities of Bi metal and HoH 2 were observed under strong reducing atmosphere, accompany with obviously decreased conductivities. Therefore, we provided here a comprehensive understanding for the multiple components doped Bi 2 O 3 -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.