High electrical conductivity in Ba2In2O5 brownmillerite based materials induced by design of a Frenkel defect structure†
To improve the electrical conductivity in the Ba2In2O5 (BIO) system without a large volume change from room temperature to 1273 K, BIO materials dually doped with Zr4+ and Zn2+ samples were prepared by using a soft chemical method. Ba2(In0.7,(Zn0.5,Zr0.5)0.3)2O5 (BIZZO-0.3) consists of an orthorhombic phase from room temperature to 1273 K. While phase transformation with a large volume change was not observed for BIZZO-0.3 in the aforementioned temperature region, the electrical conductivity observed for BIZZO-0.3 was higher than the disordered state of BIO when the measurement temperature of conductivity was more than 923 K. The effect of multiple doping on the enhancement of electrical conductivity was characterized by using the transmission electron microscopy (TEM) analysis. Also, the aforementioned effect was discussed in relation to the atomistic simulation result to explain the TEM observation results. The combination of XRD phase analysis, TEM observation and atomistic simulation indicates that a Frenkel defect cluster (i.e. ) was formed in the ordered state of the BIO lattice. It is concluded that the formation of the Frenkel defect cluster in the BIO lattice contributes to the promotion of local disordering of oxygen vacancies at the microscopic scale and maximization of electrical conductivity in the BIO system.