ELECTRONIC STRUCTURE OF Hg_0.8Pb_0.2Ba₂Ca₂Cu₃O_8+\delta: THE ROLE OF Pb DOPING, OXYGEN DOPING AND HIGH PRESSURE

The effects of Pb doping, oxygen doping (\delta= 0.1,0.2,0.4 and 0.5) and high pressate (4, 8, 15 and 20GPa) on the electronic structure of Hg_0.8Pb_0.2Ba₂Ca₂Cu₃O_8+\delta have been examined by the recursion method. Our calculations show that Pb doping only decreases the hole concentration slightly and oxygen doping increases the hole concentration monotonically and significantly as \delta varies from 0 to 0.5, with each excess oxygen atom contributing about 1.7 holes to the CuO₂ layers. The optimal \delta is estimated to be around 0.4, The hole conceatration increases initially with pres-sure but decreases as P > 8GPa (i.e., dn/dP does change sign at ～ 8GPa). The suppressed T_c(P) by Pb substitution has to be described in the modified Neumeier's model.