Abstract
is an experimentally confirmed hybrid improper ferroelectric material, in which the electric polarization is induced by a combination of the coherent octahedral rotation and tilting. In this work, we investigate the tuning of ferroelectricity of using isovalent substitutions on Ca sites. Due to the size mismatch, larger/smaller alkaline earths prefer sites, respectively, allowing the possibility for site-selective substitutions. Without extra carriers, such site-selected isovalent substitutions can significantly tune the octahedral rotation and tilting, and thus change the structure and polarization. Using the first-principles calculations, our study reveals that three substituted cases (Sr, Mg, and Sr+Mg) show divergent physical behaviors. In particular, becomes nonpolar, which can reasonably explain the suppression of polarization upon Sr substitution observed in experiment. In contrast, the polarization in is almost doubled upon substitutions, while the estimated coercivity for ferroelectric switching does not change. The remains polar but its structural space group changes, with moderate increased polarization and possible different ferroelectric switching paths. Our study reveals the subtle ferroelectricity in the family and suggests one more practical route to tune hybrid improper ferroelectricity, in addition to the strain effect.
- Received 23 January 2018
- Revised 11 April 2018
DOI:https://doi.org/10.1103/PhysRevB.97.184105
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