Tunable band structures in digital oxides with layered crystal habits

Abstract

We use density functional calculations to show heterovalent cation-order sequences enable control over band gap variations up to several electron-volts and band gap closure in the bulk band insulator LaSrAlO4. The band gap control originates from the internal electric fields induced by the digital chemical order, which induces picoscale band bending; the electric-field magnitude is mainly governed by the inequivalent charged monoxide layers afforded by the layered crystal habit. Charge transfer and ionic relaxations across these layers play secondary roles. This understanding is used to construct and validate a descriptor that captures the layer-charge variation and to predict changes in the electronic gap in layered oxides exhibiting antisite defects and in other chemistries.

Informatics-Based Learning of Oxygen Vacancy Ordering Principles in Oxygen-Deficient Perovskites

“…The reasoning behind this assumption is based on the electrostatic potential profile induced by cation ordering of the inequivalent charge states from the A and A′ cations. 120 The Cu + layer has nominal charge of +1 (unit of e/a pc 2 ), and the neighboring atomic layers is AO with a charge of 0 (neutral) if the A cation is an alkaline-earth metal, +1 if the A cation is a lanthanide, and +0.5 if the two A-cations are mixed. The internal electric field is obtained by integrating the layer charge densities, so the successive positively charged layers (which includes negative charge-dominant octahedral regions in the structure) would form an extremely high internal electric field.…”

“…The internal electric field is obtained by integrating the layer charge densities, so the successive positively charged layers (which includes negative charge-dominant octahedral regions in the structure) would form an extremely high internal electric field. 120 Thus, having lanthanides near the Cu + layer would not be a feasible solution.…”

“…Before discussing whether these cations possess suitable ionic radii, we assume the structure will adopt a A / A ′ cation order, as depicted in Figure . The reasoning behind this assumption is based on the electrostatic potential profile induced by cation ordering of the inequivalent charge states from the A and A ′ cations . The Cu + layer has nominal charge of +1 (unit of e / a pc 2 ), and the neighboring atomic layers is A O with a charge of 0 (neutral) if the A cation is an alkaline-earth metal, +1 if the A cation is a lanthanide, and +0.5 if the two A -cations are mixed.…”

“…The Cu + layer has nominal charge of +1 (unit of e / a pc 2 ), and the neighboring atomic layers is A O with a charge of 0 (neutral) if the A cation is an alkaline-earth metal, +1 if the A cation is a lanthanide, and +0.5 if the two A -cations are mixed. The internal electric field is obtained by integrating the layer charge densities, so the successive positively charged layers (which includes negative charge-dominant octahedral regions in the structure) would form an extremely high internal electric field . Thus, having lanthanides near the Cu + layer would not be a feasible solution.…”