Ferroelectricity and structure in the YMnO₃ family

The 1963 discovery of ferroelectricity in YMnO₃ was accompanied by an experimental Curie temperature (T_c) reported as 913 K; this value was revised to 1270 K in the following decade. Subsequently, YInO₃ was shown to be isostructural with YMnO₃ and later demonstrated to satisfy the structural criteria for ferroelectricity; recent unpublished measurements give T_c (YInO₃) = 835 (15) K. The experimental T_c value of 913 K for YMnO₃ is in satisfactory agreement with the calculated 1220 (100) K value as derived from a very recent structural refinement, the experimental T_c of 835 (15) K for YInO₃ with the calculated 760 (120) K. The full YMnO₃ family includes the AMnO₃ subfamily with A = Y, Ho, Er, Tm, Yb, Lu, Sc, In; the AInO₃ subfamily with A = Y, Gd, Dy, Ho, Tb; and the AGaO₃ subfamily with A = Y, Ho, Er. The T_c values of six family members with known structure, in addition to YMnO₃ and YInO₃, have been structurally derived as 1310 (110) K for ErMnO₃, 1290 (165) K for LuMnO₃, 1270 (110) K for YbMnO₃, 1220 (105) K for ScMnO₃, 540 (375) K for InMnO₃ and 1020 (100) K for YGaO₃. The agreement between predicted and experimental T_c values for ErMnO₃, LuMnO₃ and YbMnO₃, in addition to that for YMnO₃ and YInO₃, leads to the confident prediction that ScMnO₃, InMnO₃ and YGaO₃ are new ferroelectrics. The remaining six members of the full YMnO₃ family are also expected to be new ferroelectrics.