Low-temperature fully dense and electrical properties of doped-ZnO varistors by a polymerized complex method

The preparation of homogeneous and submicrometer doped-ZnO ceramic powders by using a metal-organic polymeric method is described. After calcining and granulating, green compacts with a uniform packing powder and a narrow pore size distribution were achieved. Dense ceramic bodies (>99% theoretical) by normal liquid-phase sintering at temperatures of 850–940°C for 1–5 h were fabricated. It is believed that the low pore-coordination-number allowed a uniform filling of the small pores by the formed liquid in the early stages of sintering and, as a consequence, a high shrinkage rate and rapid densification in a short temperature interval (825–850°C) took place. At those sintering temperatures a small grain growth was produced, and the grain size was maintained below 1 μm. Preliminary electrical results obtained on the doped-ZnO ceramics so fabricated showed nonlinearity coefficients α⩾70 and a breakdown voltage Vb (1 mA/cm2)⩾1500 V/mm.