Hydrothermal synthesis and structural characterization of BaTiO3 nanocrystals

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) 2000 Elsevier Science B.V. All rights reserved.