SEMIEMPIRICAL STUDY ON THE VALENCES OF CU AND BOND COVALENCY IN Y1-XCAXBA2CU3O6+Y

The valences of Cu and bond covalencies in Y1-xCaxBa2Cu3O6+y, have bee n investigated using complex chemical bond theory, This theory is the generalization of Phillips, Van Vechten, Levine, and Tanaka's scheme. The results indicate that the valences of Cu(1) and Cu(2) in our calcu lation agree well with those obtained by the bond valence sum method. The valences of Cu(1) and Cu(2) in our calculation also suggest that t he holes introduced by Ca substitution only reside in CuO2 planes and there is a competing mechanism for the hole density in CuO2 planes bet ween,Ca doping and oxygen depletion. These conclusions are in satisfac tory agreement with experiments. The calculated ordering of covalencie s is )-O(4)>Cu(1)-O(1)>Cu(2)-O(2,3)>Cu(2)-O(1)>Ca-O>Y-O similar to Ba- O, regardless of the Ca doping level and oxygen content. [S0163-1829(9 8)03325-6].