Effect of aliovalent doping on the transport properties of lanthanum cuprates

Cuprates with perovskite-related structure and the general formula La(1-x)A(x)Cu(1-y)B(y)O(2.5+/-delta) (A=Ca, Ba, Sr; B=Li; x=0.1, 0.2, 0.3; y=0, 0.1) were prepared by the citrate route. Their structures were studied by X-ray powder diffraction and their electrical conductivities (as a function of temperature) by four-point DC measurements on sintered bars. The highest values of electrical conductivity were observed for the x=0.3 Sr-doped cuprate, which showed a metallike temperature dependence. Ba-doped cuprates showed a transition from semi-conducting to metallic temperature dependence of conductivity. The extent of A-site deficiency is small and had the effect of slightly decreasing the conductivity and thermal expansion coefficient. Li solubility was also found to be small, but it reduced conductivity drastically, due in part to the disruption of the copper-oxygen conductive network. Reactions between cuprates and a typical manganite fuel cell cathode, and Pt and Pd contacts were observed at 1,000 degrees C.