2 PHASE COEXISTENCE IN YBA2(CU1-XCOX)(3)O-7-DELTA SUPERCONDUCTOR WITHX=0.03

Co-doped impurity-free YBa2(Cu1-xCox)(3)O-7-delta(123Co(x)) with x = 0 .03 superconducting samples have been synthesized using conventional s olid state reaction techniques. A Rietveld analysis of X-ray diffracti on data for these specimens reveals that two structures (one tetragona l represented by T-YBCO, and the other orthorhombic represented by O-Y BCO) co-exist at this composition of the cuprate. The use of a single tetragonal or single orthorhombic structure as the model for the refin ements does not produce acceptable fits to the X-ray diffraction patte rn. The refinements show that the T-YBCO phase at 298 K has tetragonal symmetry (P4/mmm) with a = 0.387879(4) nm, c = 1.17314(1) nm, and tha t the O-YBCO phase has at 298 K an orthorhombic symmetry (Pmmm) with a = 0.387555(4) nm, b = 0.389400(4)nm, c = 1.17363(1) nm, respectively.