Synthesis of new brownmillerite-type systems A₂(M,M')₂O₅ (A = Ba, Sr; M = Zn; M'= Zr, Ce, Ti, Hf, Sn)

抄録

  Oxide ion conductor has been desired for application to solid oxide fule cells (SOFCs), which can be operated at temperatures below 873K. In order to obtain a new oxide-ion conductor, di-(M) and tetra-(M') valent cations were co-doped to the In-site of Ba₂In₂O₅ which is known to be high oxide-ion conductor at high temperature above 1203K. The A₂(M,M')₂O₅ systems (A＝Ba, Sr; M=Zn, ; M'=Zr, Ce, Ti. Hf, Sn) having a brownmillerite-type compositions were prepared by solid state reaction. X-ray diffraction analyses confirmed that only the combinations of (Ba-Zn-Zr), (Ba-Zr-Ce), (Ba-Zn-Hf), (Sr-Zn-Zr), (Sr-Zn-Ti) and (Sr-Zn-Hf) for the A-M-M' in the present systems showed single phases of cubic or orthorhombic perovskite-type structures at room temperature. It was found that the electrical comductivities of the new phases increased with increasing the unit cell free volume.