The impact of calcination temperature on electrical conductivity and phase stability in double-doped (Bi 2 O 3 ) x-y (Er 2 O 3 ) x (Ho 2 O 3 ) y solid electrolytes

In the study, we synthesized the (BiO 1.5 ) 0.88 (ErO 1.5 ) 0.08 (HoO 1.5 ) 0.04 and (BiO 1.5 ) 0.88 (ErO 1.5 ) 0.04 (HoO 1.5 ) 0.08 ternary compositions using the solid-state reactions in an atmosphere of air. All compositions were then heated to 650, 700, 750, and 800 degrees C to observe how the calcination temperature impacts phase stability and conductivity. All XRD patterns suggested that the cubic 6- phase, a high-ion conductor, became stable at room temperature. Depending on the temperature, the DTA curves revealed that some compositions had an endothermic peak at around 600 degrees C, indicating an order-disorder transition wholly related to anion sublattice arrangement without a phase transition. At 700 degrees C, the highest conductivity was found to be 0.482 S/cm for the (BiO 1.5 ) 0.88 (ErO 1.5 ) 0.04 (HoO 1.5 ) 0.08 composition calcined at 800 degrees C, and this conductivity is greater than that of a single-doped (BiO 1.5 ) 0.80 (ErO 1.5 ) 0.20 system. The FE-SEM images indicated that calcination at 650 degrees C and 700 degrees C, which are below the phase transition temperature (729 degrees C) from alpha - phase to cubic 6- phase, results in atom aggregation and porosity on the surface. Besides, the calcination temperature was shown to significantly impact grain sizes, with compositions produced with a calcination at 800 degrees C exhibiting bigger grains than lower ones.