Structural, dielectric and impedance study of Bi and Li co-substituted Ba_0.50Sr_0.50TiO₃ ceramics for tunable microwave devices applications

In this article, the structural, dielectric and electrical properties of Bi and Li co-substituted (Ba, Sr) site in Ba_0.50Sr_0.50TiO₃ ceramics are presented. Four different compositions of Ba_0.50Sr_0.50TiO₃, (Ba_0.50Sr_0.50)_0.98(Bi, Li)_0.02TiO₃, (Ba_0.50Sr_0.50)_0.96(Bi, Li)_0.04TiO_3, and (Ba_0.50Sr_0.50)_0.92(Bi, Li)_0.08TiO₃ were synthesized using solid-state reaction with microwave heating of starting materials. Phase detection for all samples has been examined by XRD along with Rietveld refinement analyses, and the results show the formation of single phase without observation of any secondary phase. However, a decrease in crystallite size, lattice parameters, and unit cell volume has been observed with the increase of Bi and Li concentration. A Dense microstructure with different grains sizes and shapes has been obtained by scanning electron microscopy. Impedance spectroscopy in the temperature range of 30–300 °C and frequency range of 60 Hz–1 MHz has been used to study the dielectric properties. The result shows that the Bi and Li co-substituted Ba_0.5Sr_0.5TiO₃ ceramics exhibit very interesting features, such as enhanced dielectric constant with low loss which make it suitable for microwave tunable devices applications. An electric impedance analysis was carried out at different temperatures namely (400, 450, 500, and 550 °C). A single semicircular arc with single relaxation process has been observed in all studied samples which suggest that the grains contribute to the total resistance in these materials. The activation energy was obtained from the impedance analysis using Arrhenius plot of grain conductivity.