Barium titanate (BaTiO3:BT) nanocrystals were tailored by hydrothermal meth
od in the presence of polyoxyethylene (20) sorbitan monooleate (Tween(R) 80
) as a polymeric surface modifier at 230 degrees C for 0.5-2 h. The mean pa
rticle size was 77.8 +/- 23.5 nm by transmission electron microscopy (TEM),
and 83 +/- 19 nm by laser-scattering particle size analyzer. The narrow pa
rticle size distribution of the nanocrystals suggested that further growth
and agglomeration of crystals have been hindered by the surface modifier. T
hese nanocrystals were identified as metastable cubic phase BT by X-ray dif
fractometry (XRD) and differential scanning calorimetry (DSC). However, Ram
an-active modes of tetragonal phase BT were detected from Raman spectra of
as-prepared nanocrystals. Large strains have been observed in TEM dark fiel
d image, indicative of a structural deformation from metastable cubic phase
to tetragonal phase. The results suggest that the hydrothermally synthesiz
ed BT nanocrystals are metastable cubic phase with some tetragonality. (C)
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