Supertetragonal Phases of Perovskite Oxides: Insights from Electronic Structure Calculations

Abstract

We review some of the insights that electronicstructure calculations has brought about the properties of the materials with the largest electric polarization knownsupertetragonal perovskite oxides. These are materials whose structure corresponds to a perovskite that has been substantially strechted along one of its pseudocubic axes. They grow in different forms: bulk crystals (such as BiCoO 3), epitaxial films (such as BiFeO 3), nanowires whose inside is under negative pressure (such as PbTiO 3), and others. Electronic structure calculations based on density-functional theory have revealed that supertetragonality potentially exist for many perovskite oxides under the right conditions, and they have helped explain why some of those conditions are easy to reach for some of the materials of the family, but not for others.

Epitaxial ferroelectric interfacial devices

“…Two particular reports are striking, namely, for supertetragonal PbTiO 3 and BiFeO 3 , where ferroelectric polarizations of 236 µC/cm 2 and 130 µC/cm 2 , respectively, have been reported, 240,439 consistent with first principles calculations. 234,440,441 In addition to modifying the ferroelectric polarization, epitaxial strain also affects the ferroelectric critical temperature by hindering the transition to the higher symmetry paraelectric phase, while the order of the phase transition may change from first to second order as a consequence of the reduced electrostrictive coupling in strained ferroelectric films; [442][443][444] intuitively speaking, epitaxial prevents the system to lower the crystal symmetry to cubic Epitaxial ferroelectric interfacial devices Reproduced with permission from Phys. Rev.…”

Comparative density functional studies of BiMO3 polymorphs (M = Al, Ga, In) based on LDA, GGA, and meta-GGA functionals

“…Such structures are called supertetragonal. 29 In the case of BiInO 3 , there are only two phases within the range of 100 meV f.u. −1 of the orthorhombic Pna 2 1 ground state.…”

“…27 The theoretical description of oxides by means of density functional theory is a complex and challenging issue. [28][29][30] The results often depend on the choice of exchange-correlation (XC) functionals. 9,[30][31][32] In general, the XC functionals form a hierarchy of approximations.…”

On the origin of supertetragonality in BaTiO$_3$

“…The origin of these supertetragonal phases remains poorly understood, with many authors suggesting the breaking of the bond along the tetragonal axis [39,45,46], albeit ill-defined what is meant. In case of a true broken bond along the c-axis of the long Ti−O bond, the coordination number of Ti would reduce to 5, giving rise to a layered structure.…”