Growth of nanofibrous barium carbonate on calcium carbonate seeds

Fibrous barium carbonate (BaCO3/witherite) crystals 50-100 nm in diameter and several microns in length were grown on calcium carbonate (CaCO3) seeds at temperatures as low as 4 °C. The BaCO3 fibers were deposited onto calcite rhombs or CaCO3 films using the polymer-induced liquid-precursor (PILP) process, which was induced with the sodium salt of polyacrylic acid (PAA). The structure and morphology of the resultant fibers were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and polarized light microscopy (PLM). Fibers were successfully grown on calcite seeds of various morphologies, with a range of barium concentrations, and PAA molecular weight and concentration. Two categories of fibers were grown: straight and twisted. Both types of fibers displayed single-crystalline SAED diffraction patterns, but after examining high-resolution TEM lattice images, it was revealed that the fibers were in fact made up of nanocrystalline domains. We postulate that these nanocrystalline domains are well aligned due to a singular nucleation event (i.e., each fiber propagates from a single nucleation event on the seed crystal) with the nanocrystalline domains resulting from stresses caused by dehydration during crystallization of the highly hydrated precursor phase. These BaCO3 fibers grown on calcite substrates further illustrate the robustness and non-specificity of the PILP process.