The stability of the CuO2 plane and its influence on superconductivity in the doped YBa2Cu3O7-δ system

It is discovered in seven codoped Y-123 systems, Y1-xCaxBa2-xLaxCu3Oz, Y1-xCaxBa2Cu3-xAlxOz, YBa2-xLaxCu3-xAlxOz, Y1-xCaxBa2Cu3-xNixOz, YBa2-xLaxCu3-xNixOz, Y1-xCaxBa2Cu3-xZnxOz, and YBa2-xLaxCu3-xZnxOz, that the neighboring atoms, Cu(2), O(2) and O(3), form a steady 'fixed triangle' local structure in the CuO2 plane. The reason for the existence of this steady structure is briefly discussed. For each system, the rate of decrease of T-c with doping is closely related to the triangle's stability, which is defined as the average fluctuation of the three bond lengths involved in the triangle. The results imply an underlying correlation between the stability of the Cu(2)-O(2)-O(3) triangle and the high T-c superconductivity.