1 -x)MgTiO 3 -xCa 0.8 Sr 0.2 TiO 3 (0.04 ≤ x ≤ 0.2, MT-CST) composite ceramics were prepared by the conventional solidstate reaction process. The phase composition, microwave dielectric properties, and microwave dielectric loss mechanisms were studied. Ca 0.8 Sr 0.2 TiO 3 was employed as a s f compensator for MgTiO 3 , and they coexisted well without forming any secondary phases. Interestingly, significant dielectric relaxations associated with oxygen vacancy defects were observed in all the MT-CST ceramics through the dielectric-temperature spectra. Thermally simulated depolarization current was therefore conducted to obtain the defects associated with extrinsic dielectric loss mechanisms. The concentrations of both defect dipole ½ðTi 0 Ti Þ À ðV O Þ and in-grain oxygen vacancies ðV O Þ increased with the increasing x, which could induce microwave dielectric loss consequently. It demonstrated that the behaviors of Q 3 f were basically influenced by phase composition and defects here. Temperature-stable ceramics can be achieved at x = 0.06, where the microwave dielectric properties were e r = 21.19, Q 3 f = 110 900 GHz (f = 9.295 GHz), and s f = -0.9 ppm/°C, respectively.
P. Davies-contributing editorManuscript No. 35752.
A novel, three‐phase, double‐percolating composite with NiZn‐ferrite particles and nickel particles embedded in a poly(vinylidene fluoride) matrix is prepared by a simple hot‐pressing method. Large ferrite particles in the composite not only act as a magnetic phase, thus endowing the composite with a high initial permeability, but also present (in a high volume fraction) a discrete (non‐percolating) phase, confining polymer and metallic particles into a continuous double‐percolating structure of low volume fraction. In particular, a large enhancement in both the initial permeability and the dielectric constant of the three‐phase composites is observed, which is due mainly to the addition of a small number of nickel particles that act as both magnetic and percolative metallic phases. The dielectric and magnetic behavior observed in the three‐phase composites can be explained by effective‐medium and percolation theories.
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