The simulation of a possible change in a structural phase of superconducting compound YBa₂Cu_3-yPb_yO_6.5+d was done for the samples prepared by solid-state reaction represented by (y=0-0.5). Theoretically, the probability structural phase was derived from a pure structure YBa₂Cu₃O_6.5+d, which had an orthorhombic phase with lattice constants (a=3.8203, b=3.8855, and c= 11.6835 Å) and space group Pmmm. There is a partial variation in the orthorhombic unit cell from the pure phase through the substitution of Pb. There is a structural phase transition from orthorhombic to tetragonal phase at (y=0.2, 0.3). The limited variation in the lattice constant is around the theoretical values with the orthorhombic phase. The valency (+2) of Pb-ions took place in the position of Cu⁺²-ion in the composition YBa₂Cu_3-yPb_yO_6.5+d. There is a sharp increase in the lattice constants (b, c) at y=0.4 with the remaining orthorhombic phase and space group Pmmm. The simulation exhibited the position of atoms within the unit cell, which was a function of the bond's nature between different atoms and their effect on the conductivity behavior with Pb substitution. The results predicted a linear relation between the c-axis and oxygen excess (δ).

Keywords: Orthorhombic phase, Resistivity measurements, Lattice constants, Anisotropy, Oxygen excess