First Principal calculations on measuring the internal electric field or inter-layer potential over B-type cation octahedra in Ruddlesden-popper (RP) type layered perovskites

Abstract

The Ruddlesden–Popper (RP) type layered perovskite structure is of great importance due to its inherent multilevel cation ordering that can tune the redox couples of B site cations resulting in special electronic and electrocatalytic properties of the materials. The cation ordering introduces a type of charge ordering, that results in an internal electric field perpendicular to the layers and results in the alteration of the B-site cation redox couple in the lattice. DFT simulations were performed on RP-type NaYTiO4 in orthorhombic Pbcm lattice to understand the nature and magnitude of the internal electric field or interlayer potential generated on B site cations in 2D layered Ruddleson-Popper structure. Charge distribution studies show that transitional metals have a noticeable decrease in static Bader distribution (33 % for Y3+ & 50 % for Ti4+ atoms) while the Born effective charges increase (about 20 % for each atom) due to the effect of mobility. The charge distribution changes upon relaxation as shown by the Bader and Born charge studies, suggesting the constructive contribution of interlayer potential or internal field on net polarization. The individual altering layers, before relaxation, show a significant z component (0 0 1) of the polarization that cancels out in the superstructure. The calculated internal electric field or interlayer potential from the un-relaxed polarization value is ±0.364 eV on the TiO6 octahedra due to alternating Na2O2 and Y2O2 layer. Our findings provide the first-time estimation of structural optimization and measure of inherently present internal field or inter-layer potential generated on B-site cation polyhedron sheet that can be effectively utilized to tune the redox energies of B-site cations to alter the electronic properties and electrocatalytic activities of the compounds. © 2024 Elsevier B.V.