Electrical properties of ultrafine-grained yttria-stabilized zirconia ceramics
- PDF / 286,841 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 28 Downloads / 230 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Electrical properties of ultrafine-grained yttria-stabilized zirconia ceramics Shusheng Jiang, Walter A. Schulze, Vasantha R. W. Amarakoon, and Gregory C. Stangle School of Ceramic Engineering and Sciences, New York State College of Ceramics at Alfred University, Alfred, New York 14802 (Received 11 September 1995; accepted 7 February 1997)
Nanoparticles of yttria-doped tetragonal zirconia polycrystalline ceramics (Y-TZP) with an average crystallite size of less than 9 nm were prepared by a combustion synthesis process. Dense and fine-grained (, 200 nm) Y-TZP ceramics were obtained by fast-firing using temperatures lower than 1400 ±C and dwell times of less than 2 min. Impedance spectroscopy was employed to measure conductivities of oxygen vacancies in the grain and the grain boundary of the fine-grained Y-TZP. The relationships between the concentration of the oxygen vacancies in the grain boundary and measurable physical parameters were determined semiquantitatively. The oxygen vacancy concentrations and activation energies for the oxygen-ion conduction in the grain and the grain boundary of the fine-grained Y-TZP were found to be independent of the average grain size in the average grain-size range of 90 –200 nm. These experimental results suggest that, in order to retain the abnormally high oxygen vacancy concentrations of the Y-TZP nanoparticles and thus enhance the oxygen-ion conductivity, it may be necessary to decrease the average grain size to approximately 10 nm.
I. INTRODUCTION
Recently, there has been increasing interest in nanostructured polycrystalline materials. Fine-grained ceramics may exhibit interesting mechanical,1,2 electrical,3–5 and magnetic6,7 properties which are not observed in coarse-grained ceramics. The grain boundaries and the interfaces in ceramic or ceramic-based composite materials may play a more important role in the properties of the material than the grains themselves if the volume fraction of the grain boundaries or the interfaces in fine-grained ceramics is much higher than that in coarse-grained ceramics. For example, fine-grained, yttria-doped tetragonal zirconia polycrystalline ceramics (Y-TZP) are superplastic at elevated temperatures if the grain size is below 1 mm. Higher strain-rates and larger elongations-to-failure can be obtained by decreasing the grain size1,2,8 (or, equivalently, by increasing the volume fraction of the grain boundaries in the material). The mechanism responsible for superplasticity is grain-boundary sliding accompanied by interface-reaction-controlled diffusion.1 Yttria fully stabilized zirconia (FSZ) ceramics are also one of the most important ceramic superionic conductors for oxygen sensors and solid oxide fuel cells, due to their high oxygen-ion conductivity at elevated temperatures. Hence, yttria stabilized zirconia is one of the most thoroughly studied ultrafine-grained ceramics for which nanocrystallite oxide powders are typically used as the starting material.9–15 There have been very few studi
Data Loading...
