In–Situ Transmission Electron Microscopy Crystallization Studies of Sol–Gel‐Derived Barium Titanate Thin Films

Barium titanate (BaTiO 3 ) thin films that were derived from methoxypropoxide precursors were deposited onto (100) Si, Pt/Ti/SiO 2 /(100) Si, and molecular‐beam‐epitaxy‐grown (MBE‐grown) (100) BaTiO 3 on (100) Si substrates by spin coating. The crystallization behavior of the amorphous‐gel films was characterized using in‐situ transmission electron microscopy heating experiments, glancing‐angle X‐ray diffraction, and differential thermal analysis/thermogravimetric analysis. Amorphous‐gel films crystallized at a temperature of ∼600°C to an intermediate nanoscale (5–10 nm) barium titanium carbonate phase, presumably BaTiO 2 CO 3 , that subsequently transformed to nanocrystalline (20–60 nm) BaTiO 3 . Random nucleation in the bulk of the gel film was observed on all substrates. In addition, oriented growth of BaTiO 3 was concurrently observed on MBE‐grown BaTiO 3 on (100) Si. High‐temperature decomposition of the intermediate carbonate phase contributed to nanometer‐scale residual porosity in the films. High concentrations of water of hydrolysis inhibited the formation of the intermediate carbonate phase; however, these sols precipitated and were not suitable for spin coating.