STRUCTURE AND SUPERCONDUCTING PROPERTIES OF YBA2-XLNXCU3O7+/-DELTA (LN = LA,ND OR GD) AND (LN,LN') 3-XBA3+XCU6O14+DELTA

In YBa//2// minus //xLn//xCu//3O//7// plus or minus // delta (Ln equals La, Nd or Gd), the structure becomes tetragonal with increase in x and the T//c of the orthorhombic phase decreases with x. Membranes of (Ln,Ln')//3// minus //xBa//3// plus //xCu//6O//1//4// plus // delta (Ln equals N Gd) are generally tetragonal and nonsuperconducting. Ln//3Ba//3Cu//6O//1//4// plus // delta and LnBa//2Cu//3 O//7// plus or minus // delta (Ln equals Nd or Gd) prepared by low-temperature decomposition of nitrates are also tetragonal and nonsuperconducting. Random occupation of Ba in LnBa//2Cu//3O//7// plus or minus // delta or La//3Ba//3Cu//6O//1//4// plus // delta appears to favor the tetragonal structure. Furthermore oxygen is less labile when La partly substitutes Ba in these oxides.