Surfactant-Free Hydrothermal Synthesis of Highly Tetragonal Barium Titanate Nanowires: A Structural Investigation

Abstract

Barium titanate nanowires synthesized with a surfactant-free hydrothermal method have been characterized by various techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), synchrotron X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The TEM and SEM analyses show the uniform cylindrical nanowires. The Rietveld refinement with synchrotron X-ray powder diffraction showed that the lattice parameters of cubic and tetragonal phases were a (= b = c) = 4.0134 Å and a (= b) = 3.9998 Å, c = 4.0303 Å, respectively. The final weighted R-factor, R_wp, was 6.75% and the goodness of fit indicator was 1.30. The mass fraction of tetragonal and cubic phases based on the refined scale factor for the two phases were 98.4% and 1.6%, respectively, which clearly show the nanowires are tetragonal. The XPS analysis has shown that as-obtained BaTiO₃ nanowires were phase pure. The Raman spectra confirm the tetragonal phase of the BaTiO₃ nanowires. The dielectric constant measurement shows the shift in the transition temperature (T_c = 105 °C) compared to the bulk transition temperature (T_c = 132 °C). The dielectric constant at T_c was 174 measured at 1 kHz frequency.