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Symmetry-dependent properties such as ferroelectricity are suppressed at room temperature in Pb-free ABO 3 perovskites due to antiferrodistortive dynamics (octahedral rotations/tilts), resulting in the preferential stabilization of centrosymmetric crystals. For this reason, defect engineering (Ca doping, oxygen vacancy, etc. ) has been leveraged to break the symmetry of these crystals by inducing symmetry/structural transitions to modify the local A/B-site environment. This work demonstrates the use of in situ / ex situ photoluminescence spectroscopy to systematically detect symmetry/structural transformations in prototypical ferroelectric ABO 3 perovskites. These baseline optical responses are compared to recently synthesized Ca x Sr 1−x NbO 3 (CSNO) nanocrystals, which undergoes similar ferroelectric/structural phase transitions. Furthermore, the resultant PL response is corroborated with X-ray diffraction (XRD) and absorption spectroscopy (XAS) measurements to confirm the structural changes. This ability to directly monitor the local site symmetry within ABO 3 perovskites via photoluminescence spectroscopy can be used to screen for temperature- and defect-induced ferroelectric transitions. 

Heat management in catalysis is limited by each material's heat transfer efficiencies, resulting in energy losses despite current thermal engineering strategies. In contrast, induction heating of magnetic nanoparticles (NPs) generates heat at the surface of the catalyst where the reaction occurs, reducing waste heat via dissipation. However, the synthesis of magnetic NPs with optimal heat generation requires interfacial ligands, such as oleic acid, which act as heat sinks. Surface treatments using tetramethylammonium hydroxide (TMAOH) or pyridine are used to remove these ligands before applications in hydrophilic media. In this study, Fe3O4 NPs are surface treated to study the effect of induction heating on the catalytic oxidation of 1‐octanol. Whereas TMAOH was unsuccessful in removing oleic acid, pyridine treatment resulted in a roughly 2.5‐fold increase in heat generation and product yield. Therefore, efficient surfactant removal has profound implications in induction heating catalysis by increasing the heat transfer and available surface sites. 

The stabilization of the B-site oxidation state in ABO 3 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 (Sr 1−x NbO 3−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 Nb 4+ pervoskites. At a critical Sr to Nb ratio (Sr/Nb = 1.3), a phase transition is observed forming an oxygen-deficient SrNbO 3 phase. Structural refinement on the resultant diffraction pattern shows that the SNO NPs consists of a near equal mixture of SrNbO 3 and Sr 0.7 NbO 3−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.