Li He

Polarization relaxation mechanism of Ba0.6Sr0.4TiO3/Ni0.8Zn0.2Fe2O4 composite with giant dielectric constant and high permeability

Ba0.6Sr0.4TiO3/Ni0.8Zn0.2Fe2O4 (BST/NZO) composites were synthesized via the conventional solid-state reaction method. The phase composition and surface morphology of the composites were investigated using x-ray diffractometry and scanning electron microscope, respectively. The dielectric and magnetic properties of the composites were studied. The results show that the BST/NZO composites have giant dielectric constants and very high permeabilities. For the 10%BST/90%NZO composite, the dielectric constant and permeability in low frequency range are about 150u2009000 and 29, respectively. The giant dielectric behavior of the BST/NZO composites is mainly attributed to the Maxwell–Wagner polarization.

Hybrid processing and properties of Ni0.8Zn0.2Fe2O4/Ba0.6Sr0.4TiO3 magnetodielectric composites

Ni 0.8 Zn 0.2 Fe 2 O 4 /Ba 0.6 Sr 0.4 TiO 3 (NZO/BST) composites with high permittivity and low loss were synthesized via the hybrid processing route. The composites possess very dense and homogenous microstructure. The NZO/BST composites show good dielectric properties and magnetic properties with low loss in high frequency range. This indicates that this kind of magnetodielectric composites can be used in high-frequency communications for the capacitor-inductor integrating devices such as electromagnetic interference filters and antennas. The permittivities of the composites were also fitted using the combination of Maxwell–Wagner polarization and modified Curie–Weiss law.

Enhanced flexoelectric effect in a non-ferroelectric composite

Direct flexoelectric effect was investigated in a non-ferroelectric composite (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7/Ag (BZN/Ag) where the structure symmetry permits no macro-piezoelectricity. The flexoelectric coefficient of the BZN/Ag composite approaches 0.17u2009μC/m at room temperature. This value is 3–4 orders of magnitude higher than those of common dielectrics. Our research confirms the existence of flexoelectric effect in insulated non-ferroelectric materials except for ferroelectric relaxors.

Improved dielectric and magnetic properties of 1–3-type Ni0.5Zn0.5Fe2O4/epoxy composites for high-frequency applications

Ni0.5Zn0.5Fe2O4 (NZO)/epoxy composites with 1–3-type structure consisting of NZO rods in an epoxy matrix were fabricated by the dice and fill technique, with volume fraction from 40% to 70%. Improved frequency stability of the dielectric and magnetic properties was obtained in the frequency range from 10 MHz to 1 GHz. The optimized composite sample with 60% NZO rods in volume showed high dielectric and magnetic performance with permittivity between 9.2 and 10.3, dielectric loss between 0.09 and 0.25 in the frequency range from 50 MHz to 1 GHz, and permeability between 5.3 and 5.6, magnetic loss between 0.02 and 0.54 in the frequency range from 10 MHz to 1 GHz, respectively. Moreover, its permeability μ was increased to 170%, and the magnetic loss tan δμ was reduced to only 80% compared with the conventional 0–3-type composites with 40 vol% fillers at 1 GHz. The modelling and simulation results by Ansoft HFSS provided a reasonable explanation for the experimental results.