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 por e size distribution were achieved. Dense ceramic bodies ( > 99% theoretical ) by normal liquid-phase sintering at temperatures of 850-940 degreesC for 1-5 It were fabricated. It is believed that the low pore-coordination-numbe r 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 degreesC) took place. At those sintering temperatures a small grain growth was produced, and the grain size was maintained below I mum. Preliminary electrical resul ts obtained on the doped-ZnO ceramics so fabricated showed nonlinearity coe fficients alpha greater than or equal to 70 and a breakdown voltage V-b (1 mA/cm(2)) greater than or equal to 1500 V/mm. (C) 2001 Elsevier Science Ltd . All rights reserved.