Origin of supertetragonality in BaTiO3

Understanding ferroelectricity is of both fundamental and technological importance to further stimulate the development of new materials designs and manipulations. In this respect, supertetragonal (ST) phases with high c/a ratio of similar to 1.3 have recently resulted in outstanding ferroelectric polarization values, which urges for a microscopic origin of these novel structural phases. Here, we perform an in-depth first-principle study on the well-known ferroelectric barium titanate BaTiO3 under a hydrostatic negative pressure, showing an isosymmetric phase transition to such a ST phase. The chemical origin and driving mechanisms of this phase transition are identified as a drastic change of the covalently pi-bonded electrons. These findings provide guidance in the search for new ST phases, with great opportunities for novel multiferroic materials, and can be generalized in the understanding of other isosymmetric phase transitions.

Automated summary

Understanding ferroelectricity is important for the development of new materials and manipulations. The recent discovery of supertetragonal (ST) phases with high c/a ratio and outstanding ferroelectric polarization values has led to a need for studying the microscopic origin of these phases. A first-principle study on barium titanate under hydrostatic negative pressure reveals an isosymmetric phase transition to an ST phase, driven by a drastic change in the covalently pi-bonded electrons. These findings provide guidance for finding new ST phases and developing novel multiferroic materials, and can be applied to understanding other isosymmetric phase transitions.