Band gap engineering in SrTiO3 and related titanate perovskites has long been explored due to the intriguing properties of the materials for photocatalysis and photovoltaic applications. A popular approach in the materials chemistry community is to substitutionally dope aliovalent transition metal ions onto the B site in the lattice to alter the valence band. However, in such a scheme there is limited control over the dopant valence, and compensating defects often form. Here we demonstrate a novel technique to controllably synthesize Fe2+- and Fe3+-doped SrTiO3 thin films without formation of compensating defects by co-doping with La3+ ions on the A site. We stabilize Fe2+-doped films by doping with two La ions for every Fe dopant, and find that the Fe ions exhibit a low-spin electronic configuration, producing optical transitions in the near infrared regime and degenerate doping. The novel electronic states observed here offer a new avenue for band gap engineering in perovskites for photocatalytic and photovoltaic applications.
@article{arxiv.1510.05965,
title = {Infrared Optical Absorption in Low-spin Fe$^{2+}$-doped SrTiO${}_{3}$},
author = {Ryan B. Comes and Tiffany C. Kaspar and Steve M. Heald and Mark E. Bowden and Scott A. Chambers},
journal= {arXiv preprint arXiv:1510.05965},
year = {2016}
}