High - Temperature Transport and Defect Studies of Quadruple

High temperature electrical conductivity and Seebeck coefficient measurements were performed on the quadruple perovskites La2Ba,Cu,Sn201i, Eu2Ba2Cu,Ti,011, and La2Ba2Cu2Ti,0,, . A transition from nto p-type semiconductivity is observed for La2Ba2Cu2Sn2011 as a function of oxygen partial pressure. However, both electrons and holes contribute to the electrical properties over the entire range of experimental conditions. Both Eu2Ba2Cu2Ti,0n and La2Ba2Cu2Ti20n display p-type extrinsic semiconductivity at high oxygen partial pressures and low temperatures. A transition to lightly doped p-type, intrinsic semiconductivity occurs at low oxygen partial pressures and high temperatures. Combined conductivity and thermopower (Jonker) analysis was employed to elucidate the defect structure and the conduction parameters in these compounds. The similarity of these materials to high-Tc cuprates is discussed. D 19% Academic