Hydrothermal synthesis, phase control, and dielectric analysis of niobium-doped barium strontium titanate

In this work, the direct hydrothermal synthesis of barium strontium titanate (Ba_0.6Sr_0.4TiO₃, BST) and the niobium (Nb⁺⁵)-doped BST (Ba_0.6Sr_0.4Ti_1−xNb_xO_3, BSTNb) nanopowders, their phase control, and dielectric analysis are investigated. Pure BST has been prepared from its stoichiometric amounts of metal halide precursors and titanium oxide nanopowders in alkaline conditions at different hydrothermal temperatures and reaction times. X-ray diffraction analysis has demonstrated that different weight percentages of Nb doping in cubic-phase BST induce tetragonal distortions, enable controlled phase transformations, and improve crystallinity. Also, Raman analysis has indicated the tetragonal phase transformation induced by the Nb dopant concentrations. UV–visible absorption spectral analysis suggests a band gap narrowing from 2.9 eV to 2.0 eV, while increasing Nb⁺⁵ dopant concentration. By introducing Nb⁺⁵ ions, the lattice expands, the average size of nanoparticles decreases, and surface morphology improves, which significantly affects the total surface area and dielectric and optical properties of BST. The dielectric analysis has indicated that the dielectric constant of BST decreases, and dielectric loss increases with increasing dopant concentration due to the defect dipole formation up to a certain level, and the dielectric performance of Nb-doped BST has been found superior to that of pure BST.