Reversible Control of the Mn Oxidation State in SrTiO3 Bulk Powders

• Published in: Frontiers in chemistry Vol. 7; p. 353
• Main Authors: Mansoor, Haneen, Harrigan, William L., Lehuta, Keith A., Kittilstved, Kevin R.
• Format: Journal Article
• Language: English
• Published: Frontiers Media S.A 22.05.2019
• Subjects: Chemistry; electron paramagnetic resonance; inorganic materials; manganese; oxidation state; strontium titanate
• ISSN: 2296-2646; 2296-2646
• DOI: 10.3389/fchem.2019.00353

We demonstrate a low-temperature reduction method for exhibiting fine control over the oxidation state of substitutional Mn ions in strontium titanate (SrTiO 3 ) bulk powder. We employ NaBH 4 as the chemical reductant that causes significant changes in the oxidation state and oxygen vacancy complexation with Mn 2+ dopants at temperatures <350°C where lattice reduction is negligible. At higher reduction temperatures, we also observe the formation of Ti 3+ in the lattice by diffuse-reflectance and low-temperature electron paramagnetic resonance (EPR) spectroscopy. In addition to Mn 2+ , Mn 4+ , and the Mn 2+ complex with an oxygen vacancy, we also observe a sharp resonance in the EPR spectrum of heavily reduced Mn-doped SrTiO 3 . This sharp signal is tentatively assigned to surface superoxide ion that is formed by the surface electron transfer reaction between Ti 3+ and O 2 . The ability to control the relative amounts of various paramagnetic defects in SrTiO 3 provides many possibilities to study in a model system the impact of tunable dopant-defect interactions for spin-based electronic applications or visible-light photocatalysis.