TY: THES T1 - Sintering and electrical properties of Mn-doped and Al-doped ZnO ceramics A1 - Jiaping Han N2 - ZnO based materials have attracted much attention both in science and in technology, due to their rich properties and wide applications. The study of the sintering and electrical properties of ZnO based materials is important for their applications, such as the varistor application. The present work is concerned with the study of the sintering and electrical properties of Mn-doped and Aldoped ZnO ceramics, since these dopants play important roles in ZnO varistors. In this work, samples of undoped, Mn-doped, and Al-doped ZnO ceramics were prepared via conventional ceramic processes, and the dopants were incorporated using ethanol solutions of Mn(NO3)2.4H2O and Al(NO3)3.9H2O. The solid solution and second phases in Al-doped and Mn-doped ZnO ceramics were investigated by XRD, SEM with EDS, and TEM with EDS techniques, in order to understand their effects on the sintering and electrical properties of ZnO. The results showed that, for Al-doped ZnO, a second phase of spinel ZnAl2O4 forms at ~800?C and is stable at higher temperatures. The solid solubility of Al in ZnO was determined to be around 600 atomic ppm at 1200?C. For Mn-doped ZnO, a second phase of cubic ZnMnO3 is formed at temperatures ? 450?C and transforms into another second phase of tetragonal ZnMn2O4 at ~1100?C. The second phases gradually dissolve into the ZnO phase and are no longer detected at 1200?C in the samples with Mn contents ? 1.2 mol%. The densification and grain growth of ZnO doped with Al from 0.08 to 1.2 mol% were investigated during isothermal sintering between 1100? and 1400?C. The Al dopant significantly inhibits the grain growth of ZnO and increases the grain growth exponent from 3, for undoped ZnO, to 4 ? 6, for Aldoped ZnO. The grain growth activation energy is also changed from ~200 kJ/mol, for undoped ZnO, to ~480 kJ/mol, for Al-doped ZnO. The microstructural analysis showed that a ZnAl2O4 spinel phase exists as a second phase and that the spinel particles exert an effective drag (pinning) on the migration of ZnO grain boundaries. The analysis of the Al doping effect on the densification rate provides evidence that the driving force for densification is reduced by the second phase particles, too. A mechanism of pore-surface drag (pinning) on densification equivalent to the observed grain-boundary drag (pinning) on grain growth was proposed. [...] UR - https://ria.ua.pt/handle/10773/24986 Y1 - 2001 PB - No publisher defined