Crystallization And Grain Growth Behavior Of La2O3-doped Yttria-stabilized Zirconia

¹Department of Mechanical Engineering, Harran University, 63300, Sanliurfa, Turkey

²Metallurgical and Materials Engineering Department, Gazi University, Ankara, Turkey

³Faculty of Engineering and Architecture, Mehmet Akif Ersoy University, Burdur, Turkey

Adv. Mater. Lett., 2014, 5 (5), pp 260-264

DOI: 10.5185/amlett.2014.amwc1011

Publication Date (Web): Mar 09, 2014

Copyright © IAAM-VBRI Press

E-mail: baktas@harran.edu.tr

Abstract

The effect of La₂O₃ addition on the microstructure and grain growth behavior of yttria-stabilized zirconia (8YSZ) was investigated. To this end, 8YSZ was doped with 1–15 wt% La₂O₃ by means of colloidal processing, and then sintered at 1550 °C for 1 h. XRD results identified a dissolution limit of 5 wt% La₂O₃ in 8YSZ, the insoluble La2O3 at higher concentrations reacting with ZrO₂ during sintering to form a secondary La₂Zr₂O₇ phase. Both undoped and La₂O₃-doped 8YSZ specimens were annealed at 1400, 1500, and 1600 °C for 10, 50, and 100 h to induce grain growth. Grain growth measurement results showed that an increase in annealing temperature and holding time caused to grain growth in all specimens. Excessive grain growth was observed in the case of the undoped, and 1-5 wt% La₂O₃-doped 8YSZ specimens; however, the grain growth in 10 and 15 wt% La₂O₃-doped 8YSZ was inhibited by the formation of a pyrochloric La₂Zr₂O₇ secondary phase around the grains and grain boundaries of 8YSZ. Grain growth exponent (n) and activation energy (Q) values for grain growth of undoped 8YSZ were obtained as 3, and 358 kJ/mol, respectively, while 15 wt% La₂O₃ containing specimens had a grain growth exponent of 3, and activation energy of 413 kJ/mol. These results indicate that grain growth rate can be controlled by the addition of 10 or 15 wt% La₂O₃.

Keywords

Yttria-stabilized zirconia (8YSZ), pyrochloric La₂Zr₂O_7, grain growth, solid oxide fuel cell (SOFC).