LAYERED CUPRATES. Kenneth Poeppelmeier, Department of Chemistry and Science and Technology Center for Superconductivity, Northwestern University, Evanston, Illinois 60208

Layered copper-oxide superconductors exhibit the highest critical transition temperatures of any materials. Yet all the known double perovskites A'A"B'B"O₆ containing copper have a random or rock salt distribution of the B cations with the exception of the unique layered arrangement found in La₂CuSnO₆.¹ Only the layered arrangement contains the CuO₂^2- planes which are necessary for high-temperature superconductivity. The occurrence of layered or two-dimensional structures increases markedly when vacancies are introduced on the oxygen sublattice. Similarities among oxygen-deficient structures, especially those with two-dimensional solid-state features, will be discussed.² Combined conductivity and thermopower analysis will be presented to elucidate the unique internal chemistry, defect structure, and conduction parameters associated with the quadruple perovskites La₂Ba₂Cu₂Sn₂O₁₁, La₂Ba₂Cu₂Ti₂O₁₁ and LaYBa₂Cu₂Ti₂O₁₁.^3,4 The similarities of layered Cu-Sn and Cu-Ti perovskites to high-T_c cuprates will be presented.

1. M. T. Anderson, K. R. Poeppelmeier, S. A. Gramsch, and J. K. Burdett, J. Solid State Chem., 102, 164 (1993).

2. M. T. Anderson, J. T. Vaughey, and K. R. Poeppelmeier, Chem. Mater., 5, 151 (1993).

3. P. A. Salvador, L. Shen, T. O. Mason, K. B. Greenwood and K. R. Poeppelmeier, J. Solid State Chem., 119, 80 (1995).

4. K. B. Greenwood, G. M. Sarjeant, K. R. Poeppelmeier, P. A. Salvador, T. O. Mason, B. Dabrowski, K. Rogacki, and Z. Chen, Chem. Mater., 7, 1355 (1995).