Effect of double doping on crystal structure and electrical conductivity of CaO and WO3-doped Bi2O3

The atomic arrangement of WO3-doped Bi2O3 was found similar to that of the fluorite structure. However, the electrical conductivity of WO3-doped Bi2O3 is significantly lower than that of commonly used Y2O3-doped Bi2O3. The structure and electrical conductivity of samples formulated as (CaxW0.15Bi0.85−x)2O3.45−x (x = 0, 0.1, 0.2 and 0.3) were investigated. The as-sintered (W0.15Bi0.85)2O3.45 and (Ca0.1W0.15Bi0.75)2O3.35 exhibit similar single tetragonal structure that is isostructural with 7Bi2O3·2WO3. Therefore, (W0.15Bi0.85)2O3.45 and (Ca0.1W0.15Bi0.75)2O3.35 formed a superstructure consisting of 10 enlarged cubic fluorite subcells. However, the as-sintered samples consist of a tetragonal structure and tetragonal CaWO4 for x = 0.2 and 0.3 because the oxygen vacancy concentration increases. The conductivities of (CaxW0.15Bi0.85−x)2O3.45−x (x = 0, 0.1, 0.2 and 0.3) did not exhibit linear dependence with x value. The best conductivity is 2.35 × 10−2 S cm−1 at 700 °C for x = 0.1 that is higher than that of Ca-free (W0.15Bi0.85)2O3.45. The higher conductivity of (Ca0.1W0.15Bi0.75)2O3.35 than (W0.15Bi0.85)2O3.45 may result from the higher anion vacancy concentration and more symmetrical structure.