Solid solution and defect behavior in high Tc oxides

By combining phase composition (X-ray diffraction, electron probe microanalysis-EPMA) studies with high temperature electrical property (conductivity, Seebeck coefficient, Hall effect) measurements, insight can be gained concerning the underlying defect/charge transport mechanisms. In general, competition between electronic and anionic compensation of aliovalent dopants governs the defect structure. Systems considered include Ba-doped La2CuO4, Ce-doped Nd2CuO4, La-doped LaBa2Cu3Oy, and the compound with approximate stoichiometry Bi2Sr2CaCu2Oy. In the last instance, extensive EPMA studies had to be initially performed to establish the cation solubility limits. The La-doped LaBa2Cu3Oy system is of particular interest, given the large variability in both oxygen content and cation nonstoichiometry. In spite of the significant differences from system to system in the prevailing carrier generation mechanisms, there is a striking similarity in all of these systems in terms of carrier contents and mobilities