Abstract
Substitution mechanism have great effects on superconducting properties of HTSC. In this research a method is proposed to calculate the electrostatic energy for the high temperature superconductor in case of single and double ion simultaneous substitution with different oxidation state and studying the effect of changes in this energy by this substitution. For YBCO the substitution of Ca ion (+2e) instead Y ion (+3e ) decreases the electrostatic energy, and this effect increases with increasing concentration of Ca. Whereas the substitution of Pr ion (+4e) instead Y ion (+3e ) increases the electrostatic energy, and this effect increases with increasing concentration of Pr. The simultaneous substitution of the ion Pr (+4e) for concentration ( 0,05, 0.1,0.15 and 0.2 ) with increasing the concentration of Ca from (0 to 0.1) for each Pr concentration shows increase in the electrostatic energy, but shows decrease with increasing Ca.The decrease of the electrostatic energy is due is due to increase the free hole which leads to increase the transition temperature Tc whereas the increase of the electrostatic energy is due to decrease in the free hole which leads to decrease Tc .