First-Principles Investigation into Hybrid Improper Ferroelectricity in Ruddlesden–Popper Perovskite Chalcogenides Sr₃B₂X₇ (B = Ti, Zr, Hf; X = S, Se)

Abstract

Recently, hybrid improper ferroelectricity in layered perovskites is becoming an effective way to expand the compositional palette to find new ferroelectrics. In the present work, the ground state, electronic structure, optical properties, effective carrier masses, ferroelectric polarization, and polarization switching pathways of the Ruddlesden−Popper perovskite chalcogenides Sr 3 B 2 X 7 (B = Ti, Zr, Hf; X = S, Se) were thoroughly investigated by first-principles calculations. Some new hybrid improper ferroelectrics with the A2 1 am polar ground state, i.e.

Emergence of Rashba-/Dresselhaus effects in Ruddlesden–Popper halide perovskites with octahedral rotations

“…Note that the tilt pattern of Cmc2 1 (a − a − a 0 /a − a − a + ), corresponds to the tilt pattern of the lowenergy Pnma phase of the 3D ABX 3 perovskites, which is, however, not polar. This finding is in line with the observation that Cmc2 1 is a common ground state in perovskite oxides [56,57] and other RP perovskites [58,59]. For the allinorganic RP halide perovskite Cs 3 Sn 2 X 7 (X = I, Br), the ground state was found to be a structure with P4 2 /mnm symmetry.…”

Emerging Chalcohalide Materials for Energy Applications

“…It is different from the standard PV effect where the photogenerated charge carriers at the semiconductor p–n junction are separated by an internal built-in electric field. Notably, the direction of photocurrent in the FE-PV device can also be reversed by changing the spontaneous polarization direction with an external electrical field. , Many well-known ferroelectric materials possess the perovskite structure including halide perovskites − and recently emerging chalcogenide perovskites. − Since the dielectric constant is a measure of the of electric potential energy in the form of induced polarization, this feature increases the promise of such materials considerably . It is assumed that large dielectric constants and low effective masses would promote efficient ionization of defect states and suppress deep trap states within the bandgap .…”

“…Various synthetic methods have been applied for the synthesis of chalcohalide materials, e.g., growth from melt and vapor, self-flux, the Bridgman, chemical and physical vapor transport, sonochemical, microwave, colloidal, and solvo- and hydrothermal methods, etc. − Initially the Bridgeman-Stockbarger melt growth and the vapor growth methods were commonly used by researchers. However, these methods often necessitated a relatively long time at high temperatures as well as several grinding and igniting stages.…”