Size-dependent phase transformations in nanoscale pure and Y-doped zirconia thin films

Abstract

Phase stability in nanoscale pure zirconia and 9.5 mol.% yttria-doped zirconia (YDZ) thin films was studied by in-situ transmission electron microscopy. Oxygen vacancies are found to play a significant role in determining the microstructure and phase evolution. Pure zirconia thin films of ∼52 nm thickness were stabilized without any dopants at room temperature, whereas they transformed into a tetragonal phase upon heating to 400°C. On the other hand, 9.5% yttria doping enables stabilization of the cubic structure regardless of grain growth. Annealing of amorphous YDZ films in air (oxygen-rich) leads to tetragonal phase formation, whereas ultrahigh vacuum (oxygen-deficient) annealed samples display a cubic phase at high temperature. Detailed discussions on the effects of initial microstructure, oxygen deficiency, aliovalent doping and thickness are presented.

Acknowledgements

SR and MT are grateful to the School of Engineering and Applied Sciences, Harvard University, for financial support. AMM was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contract No. DE-AC02-05CH11231. Additionally, SR acknowledges the NCEM Visiting Scientist Fellowship that supported the microscopy done at NCEM, LBNL.