Thesis (M.Sc.)--Chulalongkorn University, 2007

Doped with Pr and La ions at the A site and Mg, Ni, Zn, and Cu ions at the B site, Ba[subscript 0.5]Sr[subscript 0.5]Co[subscript 0.8]Fe[subscript 0.2]O[subscript 3-δ] (BSCF5582) perovskites were synthesized by the modified citrate method. As the results, characterized by XRD and SEM, the Pr, La, Zn, and Cu specimens showed homogeneous and single phase with cubic perovskite structure, except Cu–doped BSCF5582 by replacing 0.1 mol Fe. O[subscript 2]–TPD results demonstrated that the oxygen vacancies can be improved by doping A site and/or B site with metal ions. The electrical conductivity of BSCF5582 doped with metal ions at A site gradually increased with the amount of the metal ions (Pr and La). However, metal doping at the B site ions decreased the electrical conductivity. Also, the oxygen vacancies and electrical conductivity of BSCF5582 doped with metals at both A and B site were less than that of only A site. Doping with 0.2 mol La at the A site of BSCF5582 gave the material with the highest electrical conductivity (419.6 S/cm at 450℃), which was about 8 times higher than that of BSCF5582 (53.7 S/cm at 500℃). At high temperature, the thermal expansions coefficient of Pr or La specimens increased with the enhancement of Pr or La contents, due to the loss of lattice oxygen that caused the formation of oxygen vacancies in the perovskite structure.