IMF2017

A common method to enhance electrostrain effect of ferroelectric materials is to place the composition to a ferroelectric-ferroelectric phase boundary (often called morphotropic phase boundary). Naturally it would be a surprise if appreciable electrostrain enhancement effect can appear in a single phase, i.e., without a phase boundary. In this talk we report such an unexpected phenomenon. We found electrostrain enhancement appears in a single rhombohedral phase region of (1-x%)Ba(Ti_0.8Hf_0.2)O₃-x%(Ba_0.7Ca_0.3)TiO₃ system. The property enhancement occurs at an “invisible boundary” in the single rhombohedral phase region in the phase diagram, which starts from the quadruple point of the system. Unlike morphotropic phase boundary or polymorphic phase boundary, there is no composition-induced or temperature-induced phase transitions associated with the “invisible boundary”. Other property anomalies are also detected at the “invisible boundary”, including maximum coercive field. The electrostrain at the “invisible boundary” exhibits better temperature stability as compared with that at a real phase boundary in the same system. The electrostrain enhancement at “invisible boundary” is discussed from Landau model and tricriticality at quadruple point. The “invisible boundary” may provide a new way to enhance electrostrain effect with better temperature stability.