“…Many transition metal ions with lower valence states occupy the B site when doped in BaTiO 3 , for example, Mn 2+ [7,8]. Similar to these dopants, Mg 2+ was also considered to be substituted for the B site as an acceptor because 6-CN Mg 2+ is closer to Ti 4+ in ionic size, and the defect notation was written as MgTi′′ according to the defect notation proposed by Kröger and Vink [9]. Considering the electroneutrality, MgTi′′ was usually compensated by one oxygen vacancy (VO••) and MgTi′′−VO•• pairs were supposed to exist in BaTiO 3 [10,11,12,13].…”