Oxygen-vacancy ordering in multiferroic Bi1−xCaxFeO3−x/2 (0.1 ⩽ x ⩽ 0.5)G. L. Cao, C. Ma, Z. Chen, H. X. Yang, H. F. Tian and J. Q. LiEPL, 102 2 (2013) 27002DOI: https://doi.org/10.1209/0295-5075/102/27002