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

With the doping of Al in ZnO for the preparation of a bulk transparent conductor target, deteriorations were observed in sinterability and uniformity. The doping of 3 wt% Al resulted in the predominance of open pores after sintering at 1300 °C. Less open pores were observed in the ZnO with 2 wt% Al, but the porosity between the inner and outer regions was not uniform due to the preferential evaporation near the surface. To improve both the sinterability and uniformity, mild (<2 MPa) pressure was applied during the preliminary heat treatment at 900 °C, before pressureless final sintering. The pressed specimens showed increased density and uniformity after the final sintering, which were higher than those of the unpressed specimens. The improvements were particularly noticeable in the 3 wt% Al and at 1250 °C, wherein the conventional densification was not successful.