Phase and Structure Evolution of Dysprosium Carbonate during Hydrothermal Processes in Dy3+–NH4+–CO32– System

Rare earth carbonates play a significant role in preparing rare earth oxides. This study examines the structure and composition of amorphous dysprosium carbonate (ADC) precursors produced through chemical precipitation. Next, how the amorphous phase changed throughout the hydrothermal process is analyzed. The precursor is identified as the Dy 2 (CO 3 ) 3 · x H 2 O with spherical morphology (40 nm), as characterized by TEM, XRD, TG-MS, and FT-IR. It was found that ADC will undergo numerous morphological and structural transformations with the progress of the hydrothermal treatment. First, a metastable Dy 2 (CO 3 ) 3 · x H 2 O is formed, and then a stable crystalline basic dysprosium carbonate Dy(OH)CO 3 is obtained. The self-assembly of amorphous precursor units results in 1D and 3D structures according to the theory of negative ion coordination. The transformation mechanism of dysprosium carbonate follows Ostwald’s rule of stages, where the metastable phase dissolves and recrystallizes to form the stable basic dysprosium carbonate phase.