Electronic Structure of Perovskite Solid Solutions (SrTiO$_{3})_{\mathrm{1-x}}$(LaTiO$_{2}$N)$_{\mathrm{x}}$

Band gap engineering of oxide perovskite materials is of great interest for electronics and photocatalysis. In this study we demonstrate that the band gap of SrTiO$_{3}$ is narrowed by mixing it with the oxinitride LaTiO$_{2}$N. Using hybrid density functional calculations, we study the electronic structure of LaTiO$_{2}$N and (SrTiO$_{3})_{\mathrm{1-x}}$(LaTiO$_{2}$N)$_{\mathrm{x}}$ solid solutions. We show that the valence-band maximum (VBM) of (SrTiO$_{3})_{\mathrm{1-x}}$(LaTiO$_{2}$N)$_{\mathrm{x}}$ is raised as the LaTiO$_{2}$N concentration increases, while the conduction-band minimum (CBM) remains almost unchanged. This is explained by the atomic orbitals that composed the VBM and CBM in the two parent compounds: in LaTiO$_{2}$N the VBM is derived from N 2p states, which are higher in energy than the O 2p that composed the VBM in SrTiO$_{3}$. The band gap of (SrTiO$_{3})_{\mathrm{1-x}}$(LaTiO$_{2}$N)$_{\mathrm{x}}$ is quantified and discussed in terms of the valence- and conduction-band offsets of SrTiO$_{3}$/LaTiO$_{2}$N.