Reversible Control of the Mn Oxidation State in SrTiO3 Bulk Powders

Abstract

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.

Regulating Mn2+/Mn4+ Activators in ZnGa2O4 via Mg2+/Ge4+ Doping to Generate Multimode Luminescence for Advanced Anti-Counterfeiting

“…According to the reported studies, the main sextet are attributed to the characteristic peaks of Mn 4+ because the isotropic g value is ∼1.996. In this work, Mn 2+ occupying the Zn site does not result in valence imbalance; thus, the oxygen defect does not appear; hence, the second group of weaker sextet peaks appearing around g = 2.00 is caused by the hyperfine coupling between the nuclear spin of Mn ( I = +5/2) and the 3d electron of Mn 2+ ions. , The characteristic peaks of Mn 2+ and Mn 4+ have been labeled in detail in the range of 320–330 mT, as shown in the inset, which is in good agreement with the results observed for SrTiO 3 bulk powders containing Mn 4+ and Mn 2+ ions. , The relative intensity of the characteristic peaks of Mn 4+ enhances with an increase in the Mg 2+ /Ge 4+ content ( x value), indicating more Mn 4+ and less Mn 2+ ions in the samples at a higher Mg 2+ /Ge 4+ content.…”

“…46,51 The characteristic peaks of Mn 2+ and Mn 4+ have been labeled in detail in the range of 320−330 mT, as shown in the inset, which is in good agreement with the results observed for SrTiO 3 bulk powders containing Mn 4+ and Mn 2+ ions. 51,52 The relative intensity of the characteristic peaks of Mn 4+ enhances with an increase in the Mg 2+ /Ge 4+ content (x value), indicating more Mn 4+ and less Mn 2+ ions in the samples at a higher Mg 2+ /Ge 4+ content. The Raman spectra of ZGMGM (x = 0−1) samples are shown in Figure 3d.…”

Fermi Level Pinning Controls Band Bending and Photochemical Charge Separation in Particles ofn-SrTiO3,n-SrTiO3:Al, andn-GaAs:Te

“…Oxygen, which has a standard reduction potential of +0.82 V vs NHE at pH 7, is a possible cause for such defects in SrTiO 3 . Adsorbed dioxygen species are commonly detected on SrTiO 3 surfaces by electron paramagnetic resonance (EPR) (superoxide) − and XPS. ,− Superoxide adsorbates (O 2 – ) form as a result of the reaction with Ti 3+ oxygen vacancy species in the SrTiO 3 lattice. On SrTiO 3 (111) single-crystal facets, this causes a Fermi shift of 0.8 eV in oxidizing direction .…”

Synthesis, Cytotoxicity Assessment and Optical Properties Characterization of Colloidal GdPO4:Mn2+, Eu3+ for High Sensitivity Luminescent Nanothermometers Operating in the Physiological Temperature Range

“…The nanoparticle concentrations seemed to have no clear relation to this phenomenon. The possible explanation to this fact may be the dye-particle interactions [50], changes in numerous enzymes, energy homeostasis, or oxidative stress [41]. Although a preliminary experiment showed no interaction between the particles and MTT in an acellular system, the other potential factors could not be entirely excluded [51].…”

“…The first step consisted of the precipitation of monodisperse hydroxycarbonates using an excess of urea and a precipitation temperature up to 90 • C. In the second step, the pH of the aqueous hydroxycarbonates slurry was reduced to pH = 4. The slightly acidic condition prevented the formation of a core-shell type material as in the case of the synthesis shown in [41]. Metal hydroxycarbonates were synthesized via homogeneous precipitation of lanthanide nitrates and manganese carbonate.…”