Anion-order driven polar interfaces at LaTiO$_2$N surfaces

TL;DR

This study uses density functional theory to explore how different anion arrangements at LaTiO$_2$N surfaces influence interface polarity and electronic properties, with implications for photocatalytic water splitting.

Contribution

It reveals how anion order influences polar interfaces in LaTiO$_2$N, showing potential for engineering interfaces with desirable electronic properties.

Findings

Ti-terminated surfaces adopt trans layers improving oxygen evolution

Interfaces between cis and trans anion orders can induce electronic reconstructions

Engineered anion order interfaces mimic phenomena seen in oxide heterostructures

Abstract

Perovskite oxynitrides have recently attracted attention for their ability to photocatalytically split water. Compared to oxides the arrangement of anions in the material represents a further structural degree of freedom. The bulk oxynitride LaTiO$_2$N prefers a bonding-dominated \textit{cis} nitrogen arrangement, while we have previously shown that the (001) surface prefers a non-polar \textit{trans} order to compensate polarity. Here we consider, using density functional theory calculations, the polar/non-polar interface that would necessarily be present between the two anion orders. We show that the Ti-terminated surface will adopt up to two \textit{trans} ordered surface layers, which has a beneficial effect on the oxygen evolution efficiency. We then consider the hypothetical case of a polar \textit{cis} ordered surface layer atop a non-polar \textit{trans} bulk and show that similar electronic reconstructions as in the LaAlO$_3$/SrTiO$_3$ interface can be expected when interfaces between different anion orders are engineered in one and the same oxynitride material.