beta-Al2TiO5 thin films were obtained by dip-coating silicon substrates in
acid-catalyzed precursor sols of aluminum and titanium alkoxides with and w
ithout acetyl acetone as a chelating agent and subsequent firing at 700 deg
rees C. Nuclear magnetic resonance and mass spectra of the precursor sols d
emonstrated that synthesis without a chelating agent leads to the most exte
nsive polymerization. X-ray photoelectron spectroscopy depth profiles showe
d that the composition of the films was homogeneous throughout their thickn
esses. The crystallization of the films was studied as a function of the fi
ring time and temperature. The films were amorphous up to 600 degrees C and
, crystalline beta-Al2TiO5 was formed at 700 degrees C. From 800 up to 1200
degrees C, titania (anatase and rutile) :phases were also detected, withou
t decomposition of the metastable beta-Al2TiO5, phase. The films fabricated
from the sols without chelating agents showed a lower tendency to decompos
e into the thermodynamically stable phases rutile titania and alpha-Al2O3.
The formation of beta-Al2TiO5 at low temperatures is attributed to a diffus
ion-limited crystallization process, which takes place in the conditions of
high homogeneity at the molecular level reached in the sol-gel synthesis a
s shown by spectroscopic analysis.