Search for Novel Phases in Y-Ba-Cu-O Family.

In order to search for possible residual minor phases in the Y-Ba-Cu-O family, powdered mixtures of Y₂O₃ + BaCO₃ + CuO and, independently, superconducting compound YBa₂Cu₃O_7−x have been treated in evacuated cells and elevated temperatures. YBa₂Cu₃O_7−x was reduced to YBa₂Cu₃O₅ by use of the special home-designed Taconis–Knudsen vacuum device. Subsequent doping by oxygen converts produced insulator YBa₂Cu₃O₅ to semiconductor or metal YBa₂Cu₃O_5+x (0 < x < 0.3). In addition to YBa₂Cu₃O₅, 0.05 volume percent of the minor delafossite phase Y₂Cu₂O₄ was spotted in the powder mixture 1/2 Y₂O₃ + 2BaCO₃ + 6Cu₂O, heated up to 818 °C in an inert gas atmosphere. An attempt to prepare the insulating bulk delafossite samples was successful, and subsequent doping by oxygen produced novel metallic phases. [ABSTRACT FROM AUTHOR]