Understanding the Crystallization Mechanism of Delafossite CuGaO₂ for Controlled Hydrothermal Synthesis of Nanoparticles and Nanoplates

Abstract

The delafossite CuGaO₂ is an important p-type transparent conducting oxide for both fundamental science and industrial applications. An emerging application is for p-type dye-sensitized solar cells. Obtaining delafossite CuGaO₂ nanoparticles is challenging but desirable for efficient dye loading. In this work, the phase formation and crystal growth mechanism of delafossite CuGaO₂ under low-temperature (<250 °C) hydrothermal conditions are systematically studied. The stabilization of Cu^I cations in aqueous solution and the controlling of the hydrolysis of Ga^III species are two crucial factors that determine the phase formation. The oriented attachment (OA) growth is proposed as the crystal growth mechanism to explain the formation of large CuGaO₂ nanoplates. Importantly, by suppressing this OA process, delafossite CuGaO₂ nanoparticles that are 20 nm in size were successfully synthesized for the first time. Moreover, considering the structural and chemical similarities between the Cu-based delafossite series compounds, the understanding of the hydrothermal chemistry and crystallization mechanism of CuGaO₂ should also benefit syntheses of other similar delafossites such as CuAlO₂ and CuScO₂