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Role of Ca off-centering in tuning the ferroelectric phase transitions in Ba(Zr,Ti)O3 system

We here report the substitution effects of the smaller Ca for the bulky Ba in (Ba1-xCax)(Ti1-yZry)O3 perovskite oxides for two systems (Ba1-xCax)TiO3 with y=0 and (Ba1-xCax)(Ti0.9Zr0.1)O3 with y=0.1. Ca off-centering was found to play a critical role in stabilizing the ferroelectric phase and tuning the polarization states in both systems. It was demonstrated that the atomic displacement due to Ca off-centering in the bulky Ba-site in the perovskite structure provides an effective approach to compensate the reduction of ferroelectricity due to the chemical pressure, which allows to keep the Curie point nearly constant in the (Ba1-xCax)TiO3 system and increase the Curie point in the (Ba1-xCax)(Ti0.9Zr0.1)O3 system. It was commonly observed that the Ca off-centering effects lead to the shift of the R-O and O-T phase transitions toward lower temperatures and the ferroelectric stability of the T-phase, resulting in the occurrence of quantum phase transitions with interesting physics phenomena at low temperatures in the (Ba1-xCax)TiO3 system and the great enhancement of electromechanical coupling effects around room temperature in the (Ba1-xCax)(Ti0.9Zr0.1)O3 system over a wide composition range of the Ca-concentration. These finding may be of great interest for the design of the green piezoelectric materials.