Structural transitions in hybrid improper ferroelectric Ca${}_3$Ti${}_2$O${}_7$ tuned by site-selective iso-valent substitutions: a first-principles study

Abstract

Ca${}_3$Ti${}_2$O${}_7$ is an experimentally confirmed hybrid improper ferroelectric material, in which the electric polarization is induced by a combination of the coherent TiO${}_6$ octahedral rotation and tilting. In this work, we investigate the tuning of ferroelectricity of Ca${}_3$Ti${}_2$O${}_7$ using iso-valent substitutions on Ca-sites. Due to the size mismatch, larger/smaller alkaline earths prefer $A$'/$A$ sites respectively, allowing the possibility for site-selective substitutions. Without extra carriers, such site-selected iso-valent substitutions can significantly tune the TiO${}_6$ 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, Sr+Mg) show divergent physical behaviors. In particular, (CaTiO${}_3$)${}_2$SrO becomes non-polar, which can reasonably explain the suppression of polarization upon Sr substitution observed in experiment. In contrast, the polarization in (MgTiO${}_3$)${}_2$CaO is almost doubled upon substitutions, while the estimated coercivity for ferroelectric switching does not change. The (MgTiO${}_3$)${}_2$SrO 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 $A_3$Ti${}_2$O${}_7$ family and suggests one more practical route to tune hybrid improper ferroelectricity, in addition to the strain effect.

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Cited by in corpus (6)

• Suppressing The Ferroelectric Switching Barrier in Hybrid Improper Ferroelectrics
• Structural transitions in hybrid improper ferroelectric Ca${}_3$Ti${}_2$O${}_7$ tuned by site-selective iso-valent substitutions: a first-principles study
• A new symmetry-based framework for discovering minimum energy pathways
• Mapping the structural transitions controlled by the trilinear coupling in Ca3-xSrxTi2O7
• Stabilization of layered perovskite structures via strontium substitution in Ca${}_3$Ti${}_2$O${}_7$ revealed via elemental mapping
• Charged domain boundaries stabilized by translational symmetry breaking in the hybrid improper ferroelectric Ca${}_{3-x}$Sr${}_x$Ti${}_2$O${}_7$