In situ TEM imaging of CaCO 3 nucleation reveals coexistence of direct and indirect pathways

Mechanisms of nucleation from electrolyte solutions have been debated for more than a century. Recent discoveries of amorphous precursors and evidence for cluster aggregation and liquid-liquid separation contradict common assumptions of classical nucleation theory. Using in situ transmission electron microscopy (TEM) to explore calcium carbonate (CaCO3) nucleation in a cell that enables reagent mixing, we demonstrate that multiple nucleation pathways are simultaneously operative, including formation both directly from solution and indirectly through transformation of amorphous and crystalline precursors. However, an amorphous-to-calcite transformation is not observed. The behavior of amorphous calcium…

• UD
  U.S. Department of Energy
• OO
  Office of Science
• BE
  Basic Energy Sciences