Reversible Control of the Mn Oxidation State in SrTiO Bulk Powders.

We demonstrate a low-temperature reduction method for exhibiting fine control over the oxidation state of substitutional Mn ions in strontium titanate (SrTiO) bulk powder. We employ NaBH as the chemical reductant that causes significant changes in the oxidation state and oxygen vacancy complexation with Mn dopants at temperatures <350°C where lattice reduction is negligible. At higher reduction temperatures, we also observe the formation of Ti in the lattice by diffuse-reflectance and low-temperature electron paramagnetic resonance (EPR) spectroscopy.

Spectroscopic Study of the Reversible Chemical Reduction and Reoxidation of Substitutional Cr Ions in SrTiO.

The solid-state synthesis and controllable speciation of Cr dopants in the layered perovskite SrTiO is reported. We employed a chemical reduction procedure with NaBH at relatively mild temperatures (<450 °C) to impart sensitive control over the relative concentration of Cr dopants, the charge-state of oxygen-vacancy defects, and presence of Ti defects in highly reduced Cr-doped SrTiO. The electron paramagnetic resonance (EPR) spectra of the reduced powder samples reveal a 12-fold increase in the Cr concentration within the axially compressed Ti-site of the SrTiO host.

Reversible control of the chromium valence in chemically reduced Cr-doped SrTiO3 bulk powders.

The effect of chemical reduction by NaBH4 on the electronic structure of Cr-doped SrTiO3-δ bulk powders prepared by a solid-state reaction was systematically studied as a function of reduction temperature. Electron paramagnetic resonance (EPR) and diffuse reflectance spectroscopies (DRS) were utilized to monitor changes in the electronic structures of both intrinsic defects (oxygen vacancies and/or Ti(3+)) and extrinsic dopants (Cr(3+)) at different reduction temperatures. We identify the existence of two temperature regimes where changes occur within 30 min.