Structural, vibrational, and dielectric properties of Ruddlesden-PopperBa2ZrO4from first principles

Abstract

Using first-principles computational techniques, we have investigated the structural, vibrational, and dielectric properties of a Ruddlesden-Popper-type layered oxide ${\mathrm{Ba}}_{2}{\mathrm{ZrO}}_{4}$ subjected to a wide range of biaxial strains emulating epitaxial thin-film environment. Under compressive strains, this compound experiences an incommensurate distortion characterized by planar displacements of individual perovskite slabs away from their high symmetry positions. On the other hand, under increasing epitaxial tension, the original centrosymmetric structure becomes unstable---first, with respect to antiferrodistortive oxygen cage rotations and then also with respect to in-plane polar distortions. Both the incommensurate-to-commensurate and the nonpolar-to-polar phase transformations are accompanied by anomalies of the static dielectric response, however, only in the latter case a divergence of the in-plane dielectric constant is observed. Remarkably, even after the transition into the ferroelectric state (with polarization of up to 0.12 ${\mathrm{C}/\mathrm{m}}^{2}$ at 3.5% tension) dielectric permittivity of ${\mathrm{Ba}}_{2}{\mathrm{ZrO}}_{4}$ remains unusually high, which is explained by an emergence of a Goldstone-like excitation in the system manifested through an in-plane libration of the polarization vector. Since ${\mathrm{Ba}}_{2}{\mathrm{ZrO}}_{4}$ displays a yet poorly understood tendency to absorb small molecules, such as water and ${\mathrm{CO}}_{2}$, acquiring better insights into the physical underpinnings of its behavior can produce more efficient functional materials for applications in advanced technologies for carbon sequestration.