ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 35, Number 4
JKCSEZ 35(4)
August 20, 1991 

We calculated a difference between the YBa2Cu3O7-x superconductor (123 system) of critical temperature, 95 K and the YBa2Cu4O8 superconductors (124 system) of critical temperature, 80 K in Y-system superconductors using Extended Huckel Theory (EHT). The valence electron population (VEP), reduced overlap population (ROP) and net charge for the charged cluster models relating to the layer and the chain in 123 and 124 systems were compared. The VEPs of Cu atom in the layer of 123 and 124 systems populated dz2 orbital more than dx2-y2 orbital, and in the chain of 123 and 124 systems populated dy2-z2 orbital more than dz2 orbital. The ROP of the Cu(1)-O(1) in the layer of 123 system was larger than the value of the Cu(1)-O(2), but the ROP of the Cu(1)-O(2) in the layer of 124 system was larger than the value of the Cu(1)-O(1). The ROP of Cu(2)-O(4) in the chain of 123 and 124 systems were larger than the value of the Cu(2)-O(3). In 123 system the net charge values of the Cu in the layer was larger than the value of the Cu in the chain. However, in 124 system the net charge value of the Cu in the chain was larger than the value in the layer.