Owing to their exceptional property tunability and chemical stability, ABO3 perovskites have emerged as attractive candidates for energy storage and conversion devices. Recently, SrNbO3 has attracted interest for its plasmonic and low-loss response. While metallic properties are observed in its thin film analogue, SrNbO3 nanoparticles (NPs) synthesized using solution-based chemistry appear to be insulating which is attributed to the presence of Nb5+ defect sites. Although wet-chemical approaches provide a low-cost method to prepare NPs, the synthesis of ABO3 perovskites with unstable B-site oxidation state and possessing metallic responses still remains a synthetic challenge. Therefore, to address this issue, this work takes advantage of a thermal treatment method in H2/Ar atmospheres to prevent the formation of Nb5+ during the synthesis of Sr1-xNbO3-δ (SNO) nanocrystals to obtain optically active nanomaterials. SNO nanocrystals (~20 nm) were fabricated using a two-step co-precipitation/pressure-controlled molten salt technique to stabilize the Nb-site oxidation state by limiting available oxygen during the crystallization process. Next, the as-synthesized nanoparticles were annealed in reducing atmospheres (H2/Ar) to induce metallic responses. Preliminary XRD and UV-Vis spectroscopic results show that the SNO NPs exhibit lower Nb5+ concentrations and higher visual light absorption with increasing annealing time. TGA-DSC studies were performed to understand the evolving crystal structure during the reducing treatments. Furthermore, these reduced blue-color nanocrystals, which are expected to show metallic nature, are studied using electrochemical impedance spectroscopy in order to quantify changes to the NP resistivity as a result of the H2/Ar treatment. Finally, similar optoelectronic behaviors are observed with the synthesis of other metastable ABO3 perovskites, i.e. B = Ta and Mo. Overall, these structural and optoelectronic characterization results of reduced metallic SrBO3 (B = Nb, Ta, and Mo) NPs not only contributes to the elucidation of the structure-property relationship in ABO3 perovskites but also provides new insights into the understanding of coordination chemistry and metal to insulator transitions in metal oxides.

Inducing insulator to metal transitions via H2/Ar treatment in metastable ABO3 perovskite nanocrystals

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.