On the origin of supertetragonality in BaTiO$_3$

Abstract

Understanding ferroelectricity is of both fundamental and technological importance to further stimulate the development of new materials designs and manipulations. Here, we perform an indepth first-principle study on the well-known ferroelectric barium titanate BaTiO 3 under a hydrostatic negative pressure, showing an isosymmetric phase transition to a supertetragonal phase with high c/a ratio of ∼ 1.3. The microscopic origin and driving mechanisms of this phase transition are identified as a drastic change of the covalently π-bonded electrons. These findings provide guidance in the search for new supertetragonal phases, with great opportunities for novel multiferroic materials; and can be generalized in the understanding of other isosymmetric phase transitions.