CRYSTAL-STRUCTURE AND SUPERCONDUCTIVITY OF LA2-XBAXCUO4 ESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.24)

High-resolution neutron powder diffraction has been performed to inves tigate the crystal structure of La2-xBaxCuO4 as a function of x (0.03 less-than-or-equal-to x less-than-or-equal-to 0.24). The crystal param eters at 115 K refined by profile analysis show that the Cu-planar O(1 ) bond lengths decrease by 0.008 angstrom when x is increased by 0.1. This result indicates that the overlap of Cu and planar O orbitals, an d thus the charge transfer, increases with x. The length of the Cu-api cal O(2) bonds decreases at a rate of about one half of that for Cu-O( 1), suggesting that the apical oxygens O(2) also play an important rol e in the charge transfer process. The changes of the Cu-O(1) bond leng ths of the compound with x = 0.125 at 15 K are further studied in conn ection with the structural phase transition to the low-temperature tet ragonal (LTT) phase. These results are discussed in terms of their imp lication for the electronic structure and superconductivity of this sy stem.