Massive band gap variation in layered oxides through cation ordering

Abstract

The electronic band gap is a fundamental material parameter requiring control for light harvesting, conversion and transport technologies, including photovoltaics, lasers and sensors. Although traditional methods to tune band gaps rely on chemical alloying, quantum size effects, lattice mismatch or superlattice formation, the spectral variation is often limited to o1 eV, unless marked changes to composition or structure occur. Here we report large band gap changes of up to 200% or B2 eV without modifying chemical composition or use of epitaxial strain in the LaSrAlO 4 Ruddlesden-Popper oxide. First-principles calculations show that ordering electrically charged [LaO] 1 þ and neutral [SrO] 0 monoxide planes imposes internal electric fields in the layered oxides. These fields drive local atomic displacements and bond distortions that control the energy levels at the valence and conduction band edges, providing a path towards electronic structure engineering in complex oxides.

Spatially Confined Spin Polarization and magnetic sublattice control in (La,Sr)MnO3−δ Thin Films by Oxygen Vacancy Ordering

“…As shown in Table 2, the data with deviating Mn oct -O int -Mn tet angle and R value for ABO 2.67 points towards a symmetry induced rotation difference. Still, the longer Mn oct -O int bond length can reduce the coupling between octahedral and tetrahedral layers 1 , and thus enable different magnetic sublattices in these layers.…”

“…The ABO 3 perovskite structure is prone to changes in stoichiometry, and recently there has been considerable interest in layered perovskite-derived structures like the Ruddlesden-Popper, Aurivillius and Dion-Jacobsen families with cation ordering 1–3 . Layering enforces anisotropic properties in the materials by decoupling the octahedral building blocks, and enabling functional properties such as ferroelectricity 3 , ferromagnetism 4 , and superconductivity 5 , making them interesting for novel device applications such as tunable microwave filters and optoelectronic components 1, 6 .…”

“…Layering enforces anisotropic properties in the materials by decoupling the octahedral building blocks, and enabling functional properties such as ferroelectricity 3 , ferromagnetism 4 , and superconductivity 5 , making them interesting for novel device applications such as tunable microwave filters and optoelectronic components 1, 6 . Interfaces between, or superlattices of, perovskites has also been used to confine electrons into 2 dimensions resulting in a 2-dimensional electron gas, where the most studied system is the LaAlO 3 /SrTiO 3 (LAO/STO) interface 7–9 .…”

Tunable band structures in digital oxides with layered crystal habits

“…22 A total of 8 A-cation sites may be occupied by an equal number of La and Sr to give 70 total variants (including redundant structures), which are reduced down to 13 unique variants by symmetry, including 3 structures studied in Ref. 20. Fig.…”

“…Recently up to 2 eV changes in electronic band gaps were predicted in LaSrAlO 4 by changes in the A cation arrangement in the n = 1 Ruddlesden-Popper (RP) structure. 20 The A 2 BO 4 RP structure consists of alternating perovskite/rock salt components, (ABO 3 )/(AO), stacked along the [001] direction. This layered crystal habit affords stacking of [AO] and [BO 2 ] layers, which can be utilized to direct the internal electric fields by sequencing of the charged layers: [LaO] 1+ , [SrO] 0 , and [AlO 2 ] 1− .…”