STRUCTURAL STUDIES OF THE DESTRUCTION OF CU-O CHAINS IN PRBA2CU3O7 BYGA-DOPING

Structural changes of the PrBa2Cu3O7 compound as Cu are partially repl aced by Ga or Zn are studied by using high resolution neutron diffract ion measurements. Rietveld method is followed in refining the diffract ion patterns. Ga atom is found to enter the Cu site in the CuO-chain l ayers, that also causes the O in that layer to become disorder with eq ual probability to occupy the sites along the a and along the b axis d irections. This effectively destroys the Cu-O chain ordering observed in the undoped system, and results in (Cu/Ga)-O chains run in both the a and b axis directions. Tetragonal symmetry for the Ga-doped compoun d is resulted. Zn atom, on the other hand, replaces the Cu in the CuO2 -plane layer, which make no significant effect on the basic structure except a small oxygen disorder in the chain layers. The bond lengths o f Pr and the O in the CuO2-plane layers increase slightly in the Ga-do ped system, whereas that in the Zn-doped system remains basically unaf fected.