Densification and grain growth of Al-doped ZnO
- PDF / 526,560 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 58 Downloads / 214 Views
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 inhibited the grain growth of ZnO and increased the grain growth exponent from 3 for pure ZnO to 4–6 for Al-doped ZnO. The grain growth activation energy was also changed from approximately 200 kJ/mol for pure ZnO to approximately 480 kJ/mol for Al-doped ZnO. The results of x-ray diffraction, scanning electron microscopy, and transmission electron microscopy showed that a ZnAl2O4 spinel phase existed as a second phase at the ZnO grain boundaries in Al-doped ZnO specimens. The spinel particles exerted an effective drag (pinning) on the migration of ZnO grain boundaries. The analyses of the Al doping effect on the densification rate provided evidence that the driving force for densification was reduced by the second-phase particles. A mechanism of pore surface drag (pinning) on densification equivalent to the observed drag (pinning) of grain boundaries on grain growth was proposed. I. INTRODUCTION
A large number of papers1–12 on the sintering of pure and doped ZnO ceramics have been reported. The wide interest in the sintering of ZnO arises from two main reasons. On the one hand, ZnO-based materials have been developed for various technological applications, such as varistors,13 gas sensors,14 and optoelectronic devices,15 due to their electrical and optical properties. On the other hand, ZnO is an excellent model material to investigate the sintering process. It has a simple structure; ZnO powder compacts can usually reach high density after being sintered at relatively low temperature (艋1300 °C); and no phase transformation occurs during sintering. Therefore, the studies on the sintering of ZnO are important both practically and theoretically. Many studies have been conducted on the sintering of several doped ZnO systems, such as Sb-doped ZnO,1–3 Bi-doped ZnO,4 Ba-doped ZnO,5 Mn-doped ZnO,6 and Al-doped ZnO.7–10 The first researchers to study the effect of Al on the sintering of ZnO were Komatsu et al.7 They studied the isothermal shrinkage of ZnO doped with 1.2 mol% Al at temperatures of 800, 900, and 1000 °C. The grain growth of ZnO doped with 1, 2, and 10 mol% Al was investigated by Quadir and Readey8 for sintering in hydrogen between 950 and 1200 °C. They calculated the grain growth exponent and the activation energy. The grain growth of ZnO–6 wt% Bi2O3 with Al2O3 additions from 0.10 to 0.80 wt% during liquidphase sintering was investigated by Nunes and Bradt.9 They also calculated the grain growth exponent and the activation energy. However, systematic studies on the J. Mater. Res., Vol. 16, No. 2, Feb 2001
http://journals.cambridge.org
Downloaded: 02 Nov 2014
sintering of Al-doped ZnO are still lacking. In a previous work,10 nonisothermal sintering of Al-doped ZnO was studied using constant-heating-rate sintering method. The present work investigates the effects of Al dopant from 0.08 to 1.2 mol% on the densification and grain gro
Data Loading...
