A New Ferroelectric Phase of YMnO3 Induced by Oxygen-Vacancy Ordering. - Zhang, Qinghua; Guo, Sandong; Ge, Binghui; Chen, Peng; Yao, Yuan; Wang, Lijuan; Gu, Lin; Wang, Yanguo; Duan, Xiaofeng; Jin, Changqing; Liu, Banggui; Yu, Richeng; et al. (Journal of the American Ceramic Society, 2014)