Effect of double doping on crystal structure and electrical conductivity of CaO and WO_3-doped Bi_2O_3

摘要

The atomic arrangement of WO_3-doped Bi_2O_3 was found similar to that of the fluorite structure. However, the electrical conductivity of WO_3-doped Bi_2O_3 is significantly lower than that of commonly used Y_2O_3 -doped Bi_2O_3. The structure and electrical conductivity of samples formulated as (Ca_x_(0.15)Bi_(0.85-x))_2O_(3.45-x) (x=0, 0.1, 0.2 and 0.3) were investigated. The as-sintered (W_(0.15)Bi_(0.85))_2O_(3.45) and (Ca_(0.1)W_(0.15)Bi_(0.75))_2O_(3.35) exhibit similar single tetragonal structure that is isostructural with 7Bi_2O_3-2WO_3. Therefore, (W_(0.15)Bi_(0.85))_2O_(3.45) and (Ca_(0.1)W_(0.15)Bi_(0.75))_2O_(3.35) formed a superstructure consisting of 10 enlarged cubic fluorite subcells. However, the as-sintered samples consist of a tetragonal structure and tetragonal CaWO_4 forx = 0.2 and 0.3 because the oxygen vacancy concentration increases. The conductivities of (Ca_xW_(0.15)Bi_(0.85-x))_2O_(3.45-x)) , 0 = 0, 0.1, 0.2 and 0.3) did not exhibit linear dependence with x value. The best conductivity is 2.35 x 10~(-2) S cm~(-1)at 700 °C for x=0.1 that is higher than that of Ca-free (W_(0.15)Bi_(0.85))_2O_(3.45). The higher conductivity of (Ca_(0.1)W_(0.15)Bi_(0.75))_2O_(3.35) than (W_(0.15)Bi_(0.85))_2O_(3.45) may result from the higher anion vacancy concentration and more symmetrical structure.