Abstract. The results of x-ray diffraction, electrical resistance, DC and AC magnetization studies on two specimens of compositions Y2.1Ba3.9Cu6O14−δ and Y1.8Ba4.2Cu6O14−δ are presented. Our studies confirm that La3Ba3Cu6O14 type orthorhombic phase is responsible for superconductivity in the 90 K range. The heat treatment that yields high quality samples with sharp transition in electrical resistance as well as in AC magnetic susceptibility measurements is described. Magnetic response just belowTc is found to be sensitive to the measuring field.
