Temperature dependence of the hole density in high-TC superconductors Bi2−yPbySr2CaCu2O8+δ

► We have done x-ray absorption spectra on the CuL3 edge of Bi(Pb)-2212 cuprates. ► We have measured the hole density nH in the CuO2 plane of Bi(Pb)-2212 cuprates. ► The measurements were performed from 10 K to 300 K. ► Gor'kov and Teitel'baums formula of nH consists of a linear and an exponential term. ► We have extended the Gor'kov and Teitel baum formula by a T3/2 term.