First-principles study of ferroelectric and antiferrodistortive instabilities in tetragonalSrTiO3

Abstract

We carry out first-principles density-functional calculations of the antiferrodistortive ͑AFD͒ and ferroelectric ͑FE͒ soft-mode instabilities in tetragonal SrTiO 3 , with the structural degrees of freedom treated in a classical, zero-temperature framework. In particular, we use frozen-phonon calculations to make a careful study of the anisotropy of the AFD and FE mode frequencies in the tetragonal ground state, in which an R-point AFD soft phonon has condensed. Because of the anharmonic couplings, the presence of this AFD distortion substantially affects both the AFD and FE mode frequencies. The AFD mode is found to be softer for rotations around a perpendicular axis (E g mode͒ than for rotations about the tetragonal axis (A 1g mode͒, in agreement with experimental results. The FE mode, on the other hand, is found to be softer when polarized perpendicular to the tetragonal axis (E u mode͒ than parallel to it (A 2u mode͒. The sign of this frequency splitting is consistent with the experimentally reported anisotropy of the dielectric susceptibility and other evidence. Finally, we present a discussion of the influence of various types of structural distortions on the FE instability and its anisotropy.

Calculations for antiferrodistortive phase of SrTiO3perovskite: hybrid density functional study

“…These calculations considerably overestimate, by a factor of two to three, the rotation angle as well as the ratio c/a (e.g. 1.004 [17]). Simultaneously, these DFT calculations significantly underestimate the bandgap (typically, <2 eV, instead of experimental 3.3 eV) [17][18][19][20][21].…”

“…1.004 [17]). Simultaneously, these DFT calculations significantly underestimate the bandgap (typically, <2 eV, instead of experimental 3.3 eV) [17][18][19][20][21]. Surprisingly, an important question, how octahedral rotation affects the electronic bands and optical properties, has not been discussed so far, except for a single old paper [7].…”

“…These calculations have to be performed at the ab initio level due to small changes in the atomic and electronic structure, as well as relative energy changes. Recently several DFT plane-wave calculations with ultrasoft pseudopotentials [17][18][19][20] were performed. These calculations considerably overestimate, by a factor of two to three, the rotation angle as well as the ratio c/a (e.g.…”

Phase transition and random-field induced domain wall response in quantum ferroelectrics SrTi18O3: review and perspective

“…SrTiO 3 is a typical example of quantum paraelectricity [1][2][3]. Its dielectric constant saturates at a high level, 1 0 < 20000 [1], associated with the softening of a long-wavelength transverse optic phonon mode.…”

“…In this paper, we focus on the role of quantum fluctuation in SrTiO 3 , and discuss theoretical achievements in the evolution of ferroelectricity and the local symmetry of ferroelectric nanodomains as well as offering and a perspective for the future researches and applications.…”