Temperature stability, low loss and defect relaxation of MgO-TiO2 microwave dielectric ceramics modified by Ca0.8Sr0.2TiO3

Abstract Temperature-stable and low-loss microwave dielectrics based on the MgO-TiO 2 system with nominal formation Mg n +1 Ti n O 3 n +1 ( n = 5, MT) were prepared via the conventional solid-state reaction method. Ca 0.8 Sr 0.2 TiO 3 (CST) was chosen as a τ f compensator for matrix MT to form the composite ceramics (1- x )Mg 6 Ti 5 O 16 - x Ca 0.8 Sr 0.2 TiO 3 (0.10 ≤ x ≤ 0.26, MT-CST). The effects of CST additions on the phase composition, defect relaxation behavior, and microwave dielectric properties of MT were investigated. It revealed that undoped MT was basically consisted of MgTiO 3 as a major phase and Mg 2 TiO 4 as a minor phase, and such two phases coexisted well with CST additions. Interestingly, τ f could be tuned close to zero (−1.28 ppm/°C) for the MT-CST ceramics at x = 0.22, accompanied with a high Q×f value ~ 74,200 GHz and a proper e r ~ 20.25 (9.90 GHz). These materials possessed a good potential for applications in microwave components and devices. Meanwhile, significant relaxation phenomena were observed in all the MT-CST samples using dielectric spectroscopy and thermally stimulated depolarization current (TSDC) techniques. The oxygen-vacancy-related defects, shown as ( T i T i ′ )-( V O • • ) dipoles and V O • • , were the main types of defects in MT-CST, which was responsible for the relaxation behavior; meanwhile, the defect concentrations increased with the increase of CST content, thus resulting in the increase of dielectric loss at low and high frequencies.