Band gap evolution in Ruddlesden-Popper phases

Abstract

We investigate the variation of the band gap across the Ruddlesden-Popper (RP) series (An+1BnX3n+1) in model chalcogenide, oxide, and halide materials to understand the factors influencing band gap evolution. In contrast to the oxides and halides, we find the band gap of the chalcogenides evolve differently with the thickness of the perovskite blocks in these natural superlattices. We show that octahedral rotations (i.e. deviation of the B-X-B bond angles from 180 • ) and quantum confinement effects compete to decide the band gap evolution of RP phases. The insights gained here will allow us to rationally design layered perovskite phases for electronics and optoelectronics.arXiv:1905.02598v1 [cond-mat.mtrl-sci]

Discovery of highly polarizable semiconductors BaZrS3 and Ba3Zr2SFilippone1, Zhao2, Niu3 et al. 2020Phys. Rev. MaterialsSelf Cite231181View full textAdd to dashboardCite

“…The electronic contribution to the dielectric response ε elec is similar for BaZrS 3 and Ba 3 Zr 2 S 7 , although slightly larger for perovskite. This is consistent with our understanding that the electronic structures of the two phases are similar, consisting of filled sulfide 3p states at the valence band edge and unoccupied Zr 4d states at the conduction band edge [5]. This leads to similar changes in orbital hybridization (and covalency) under applied electric fields.…”

Suppressing the ferroelectric switching barrier in hybrid improper ferroelectrics

“…This shift also breaks the connectivity of the oxygen octahedra, and the AO double layer is held together by mostly ionic bonds between the A-site cations and O anions. The resulting dimensional reduction has important consequences on the electronic structure and lattice response (for example, refs [25][26][27][28] ). Apart from the dimensional effects, the different periodicity of the Ruddlesden-Popper phases along the layering direction (c-axis, or the [001] direction) leads to a smaller Brillouin zone than ABO 3 perovskites.…”

Unraveling the Suppression of Oxygen Octahedra Rotations in A3B2O7 Ruddlesden-Popper Compounds: Engineering Multiferroicity and Beyond

“…In addition, such competition may be essential for understanding recent experimental observations. First, it naturally explains the Pnmaða − a − c þ Þ → P4 2 =mnmða − b 0 c 0 =b 0 a − c 0 Þ → I4=mmmða 0 a 0 c 0 Þ transitions of Ba nþ1 Zr n S 3nþ1 as n decreases [23]. Additionally, the suppression of a 0 a 0 c þ rotations increases the bandwidth of d xy orbitals and is responsible for the decreased band gap with n ¼ 1 and 2 [23].…”

“…They can nowadays be grown with good atomic control [13,14] and recently have attracted a growing interest for accessing functional properties inaccessible in the parent ABO 3 perovskites [15][16][17][18][19][20]. Intriguingly, experiments focusing on different compounds seem to suggest a common feature: the rotations of BO 6 octahedra appearing in ABO 3 perovskites are often partly or completely suppressed in related RP structures [19][20][21][22][23]. Moreover, decreasing the tolerance factor, which typically enhances the rotations in ABO 3 perovskites, seems inefficient to recover the full rotation patterns in RP systems like SrR 2 Fe 2 O 7 (R ¼ rare-earth ion) [20].…”

“…On the one hand, suppression of the typical rotation patterns (i.e., a − a − c þ in Glazer's notations) [24] required for producing hybrid improper ferroelectricity (HIF) [15,25] limits in practice the realization of multiferroic RP compounds [20][21][22]. On the other hand, the suppression of rotations in Ba nþ1 Zr n S 3nþ1 with n ¼ 1 and 2 directly decreases the band gap to about 1.3 eV [23]. Also, negative thermal expansion (NTE) in Ca 3 Mn 2 O 7 is demonstrated to happen only in the RP phase with suppressed rotations, while it does not appear in its ABO 3 phase [19].…”