Combustion synthesis of nanostructured Ba0.8(Ca,Sr)0.2TiO3 ceramics and their dielectric properties

Ba0.8(Ca,Sr)0.2TiO3 nanostructured ceramics were synthesized by a facile and glycine-assisted auto-combustion method using stable solid TiO2, which is better than other several chemical routes reported earlier involving expensive alkoxides, oxynitrates, or chlorides of titanium as the titanium sources. TGA/DSC analysis of precursor powder gives pre-information about formation of final product around 950°C. XRD analysis confirms the formation of single-phase of the BCT and BST ceramics on sintering at 950°C for 15h. TEM image of the ceramics show nanocrystalline particles in the range 40–90nm. Surface morphology indicates that the average grain size is in range of 55–140nm and 45–120nm for BCT and BST, respectively. Energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy confirmed the purity and stoichiometry. The value of the dielectric constant of BST (εr~368) ceramic is higher than BCT (εr~255) at 100Hz at 308K. The dielectric constant BST is higher than BCT at all measured temperatures and frequency ranges due to higher crystallinity and high grain-boundary resistance, as confirmed by impedance analysis.