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Abstract:
A single-step rapid hydrothermal low-temperature process for the formation of high purity polycrystalline Ag-based delafossite oxides 3R-AgBO2 (B: Al, Ga, In) is reported. For the synthesis process reusable and widely available PTFE-lined pressure vessels are used. The presence of an elemental Ag by-phase is traced back to the metastability of the Ag-delafossite under the reaction conditions. High-purity products were obtained by decreasing the synthesis time requirements by up to 90%. The effect of the isoelectronic B-site atoms on the structure and bonding situation were comparatively studied experimentally and by ab-initio calculations. Distorted coordination environments are observed in all cases, and the nature of the chemical bond changes qualitatively along the series of group 13 B-site atoms Al, Ga, and In. This is reflected in systematic changes of the (optical) band gap, the contactless conductivity, the thermal stability, and the energetic position of Raman modes, which are strongly affected and decrease with increasing atomic number. The establishment of a facile synthesis strategy allows the application of these Ag-delafossite systems in many disciplines, i.e. in heterogeneous catalysis and as optoelectronic devices.
