(b) shows the binding state of O 1s spectra for the pure and 3 mol% Al-doped ZnO ceramics. The O 1s spectra can be resolved into three Gaussian components by XPSPEAK41 soft, which centered around 530.05 eV, 530.8 eV and 532.16 eV for pure ZnO sample, and 529.8 eV, 530.6 eV and 531.85 eV for 3 mol% Al doped sample, respectively.