Journal
PHYSICAL REVIEW B
Volume 86, Issue 9, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.86.094112
Keywords
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Funding
- DOE-BES [DE-SCOO02334]
- DGI-Spain [MAT2010-18113, CSD2007-00041]
- European Commission [EC-FP7, NMP3-SL-2009-228989]
- Francqui Foundation
- ICREA Funding Source: Custom
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We study the interplay of structural and polar distortions in hexagonal YMnO3 and short-period PbTiO3/SrTiO3 (PTO/STO) superlattices by means of first-principles calculations at constrained electric displacement field D. We find that in YMnO3 the tilts of the oxygen polyhedra produce a robustly polar ground state, which persists at any choice of the electrical boundary conditions. Conversely, in PTO/STO the antiferrodistortive instabilities alone do not break inversion symmetry, and open-circuit boundary conditions restore a nonpolar state. We suggest that this qualitative difference naturally provides a route to rationalizing the concept of improper ferroelectricity from the point of view of first-principles theory. We discuss the implications of our arguments for the design of novel multiferroic materials with enhanced functionalities and for the symmetry analysis of the phase transitions.
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