Low dielectric loss and enhanced tunable properties of Mn-doped BST/MgO composites

Ba0.6Sr0.4Ti1−xMnxO3 [BST(Mn), x = 0.0000, 0.0025, 0.0050, 0.0075, 0.0100 and 0.0125] powders were synthesized by solid-state reaction process, and then BST(Mn)/MgO ceramic composites (60 wt% MgO) were fabricated by conventional ceramic process. Mn was found distributed in the BST grains homogeneously after sintering at 1420 °C for 4 h, neither grain-boundary segregation nor diffusion into the MgO grains could be found obviously. The dielectric nonlinearity of the materials was enhanced with the addition of Mn-dopant, and relatively high tunability, more than 27% (8 kV/mm DC field, 500 Hz), was obtained in BST(Mn)/MgO samples with x ≤ 0.0100. The dielectric loss at microwave frequency of the samples with Mn-dopant was significantly reduced, and a tremendously low dielectric loss was acquired for the sample with x = 0.0050, which is only 4.5 × 10−3 (at 3.64 GHz). Both the low dielectric loss and enhanced tunable properties of the BST(Mn)/MgO composites are useful for tunable microwave applications.