Effect of the (Ba + Sr)/Ti ratio on the microwave-tunable properties of Ba sub(0.6)Sr sub(0.4)TiO sub(3) ceramics

The impact of the (Ba + Sr)/Ti (A/B) ratio on the microwave-tunable characteristics of diffuse phase transition (DPT) ferroelectric Ba sub(0.6)Sr sub(0.4)TiO sub(3) (0.6-BST) ceramics was investigated. The reduction in the lattice constant with increasing nonstoichiometry was attributed to introduced partial Schottky defects, i.e., [Formulaomitted]and [Formulaomitted]. The magnitude of the dielectric constant, epsilon ', at room temperature in the absence of an applied electric field was governed by the shift in the dielectric maximum temperature, T sub(m), because T sub(m) was close to room temperature for the 0.6-BST. The dielectric loss, tan delta , diminished as the epsilon ' decreased for 0.98 less than or equal to A/B less than or equal to 1.05, while the tan delta was much higher for A/B=0.95 having the greatest A-site vacancy loading. The negatively charged [Formulaomitted] and [Formulaomitted] were mainly compensated by oxygen vacancies and likely partly compensated by holes, h super( times ), which contributed to the electrical conduction. The tunability, T, at 100 MHz was almost constant at 20%-25% for A/B greater than or equal to 1.00 despite the reduction of the epsilon ', whereas T decreased for A/B