Valence band electronic structure of the Tl_2-x-zBa₂Ca_2+xCu₃O_10-y system

Single phase bulk Tl2223 samples were prepared in the Tl_{2-x z ̄}Ba₂Ca_2+xCu₃O_10-y system with x=0.0 to 0.4. Wet chemical analysis shows that all samples are both Tl and O deficient. The T_c is found to increase with increasing hole concentration. Ultraviolet photoemission spectroscopic (UVPES) studies of the "as synthesized" Tl_2-x-zBa₂Ca_2+x Cu₃O_10-y system have been carried out. No shifts in binding energy of valence band features are observed. Instead, doping of Ca at the Tl site creates new electronic states near the Fermi level. Tl 4f core level X-ray photoelectron spectroscopic (XPS) studies show a systematic decrease in BE with x. Systematic changes in the Cu 2p core level spectra are also observed. Possible changes in the valence band structure are suggested.