Stabilizing the B-site oxidation state in ABO3 perovskite nanoparticles

The stabilization of the B-site oxidation state in ABO3 perovskites using wet-chemical methods is a synthetic challenge, which is of fundamental and practical interest for energy storage and conversion devices. In this work, defect-controlled (Sr-deficiency and oxygen vacancies) strontium niobium(iv) oxide (Sr1-xNbO3-δ, SNO) metal oxide nanoparticles (NPs) were synthesized for the first time using a low-pressure wet-chemistry synthesis. The experiments were performed under reduced oxygen partial pressure to prevent by-product formation and with varying Sr/Nb molar ratio to favor the formation of Nb4+ pervoskites. At a critical Sr to Nb ratio (Sr/Nb = 1.3), a phase transition is observed forming an oxygen-deficient SrNbO3 phase. Structural refinement on the resultant diffraction pattern shows that the SNO NPs consists of a near equal mixture of SrNbO3 and Sr0.7NbO3-δ crystal phases. A combination of Rietveld refinement and X-ray photoelectron spectroscopy (XPS) confirmed the stabilization of the +4 oxidation state and the formation of oxygen vacancies. The Nb local site symmetry was extracted through Raman spectroscopy and modeled using DFT. As further confirmation, the particles demonstrate the expected absorption highlighting their restored optoelectronic properties. This low-pressure wet-chemical approach for stabilizing the oxidation state of a transition metal has the potential to be extended to other oxygen sensitive, low dimensional perovskite oxides with unique properties.

The role of ionic liquids in the synthesis of the high-temperature superconductor YBa2Cu3O7−δ

A deep understanding of the mechanisms of ionic liquid-mediated syntheses in the case of a high-temperature superconductor is presented.

Increase of Cr solubility in cubic Sr2FexCr2−xO6−y unit cell using sol–gel assisted synthesis and characterizations of Sr2FeCrO6−y phase

A homogeneous, non-selective chelating system using EDTA–chitosan was created to produce a cubic phase perovskite material Sr₂FeCrO_6−y.