Possible origins of superconductivity in PrBa2Cu3Ox compound viewed from results of single crystal structure study

Structural differences of the superconducting PrBa2Cu3Ox crystals grown by the TSFZ method and the semiconducting flux grown crystals were investigated using X-ray diffraction method. The TSFZ grown crystals tend to have a longer c-axis length than the flux grown crystals, in both of the as-grown and oxygen-annealed crystals. Precise structure refinement revealed that the longer c-axis length in the as-grown tetragonal TSFZ crystals is attributed to the expansion of distance between the two CuO2 planes. The Pr-O(2) bond length, however, does not show elongation. The most significant differences between the structures of the TSFZ and the flux crystals are found to be the occupancy parameter of the Cu(1) site and the thermal displacement parameter of the apical O(4) atom, implying a close relation of these structural parameters to the different electronic properties of the two crystals. (orig.)