Anion-order driven polar interfaces at LaTiO2N surfaces

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 LaTiO₂N prefers a bonding-dominated cis nitrogen arrangement, while we have previously shown that the (001) surface prefers a non-polar 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 trans ordered surface layers, which has a beneficial effect on the oxygen evolution efficiency. We then consider the hypothetical case of a polar cis ordered surface layer atop a non-polar trans bulk and show that similar electronic reconstructions as in the LaAlO₃/SrTiO₃ interface can be expected when interfaces between different anion orders are engineered in one and the same oxynitride material.