Preparation and formation mechanism of silver gallium selenide powders prepared via the sol-gel method

The sol-gel method followed by selenization was developed to synthesize AgGaSe2 powders in this study. The molar ratio of gallium ions to silver ions was controlled to prepare pure AgGaSe2 powders. Two selenization processes were employed to investigate the formed phases of the obtained powders. When the sol-gel-derived precursors were mixed with selenium powders, pure-phase AgGaSe2 powders were formed after selenization. Without mixing selenium powders, AgGaSe2 was produced with the impurity phase of Ag9GaSe6. A three-step reaction mechanism for the formation of AgGaSe2 is proposed. Ag2Se is initially formed in the first step, and then reacts with constituent species as well as hydrogen to produce Ag9GaSe6. Finally AgGaSe2 is formed from the reaction among Ag9GaSe6, Ga2O3, Se and H2. When the selenium powders are mixed with the precursors, liquid selenium is formed in the selenization process and effectively promotes the reactions.