Densification of Al-doped ZnO via preliminary heat treatment under external pressure

► By applying the mild (<2 MPa) pressure during preliminary heat treatment, the final sintering temperature required to achieve same density was reduced in Al doped ZnO. ► With the decrease of the final sintering temperature, porous layer disappeared from the outer region resulting in the improved uniformity of whole specimen. ► The improvements of density were pronounced at 3 wt% of Al and at 1250 °C of final sintering temperature, where the conventional densification was not effective.