BaTiO₃-based Multiphase Composites With Super High Dielectric Constants

Dielectric materials are mainly used for capacitors and electrical insulators. The incessant development of electronical industries and electric power industries calls for electronic components such as capacitors with high capacitance and small size. To satisfy these requirements, high dielectric constant composites attract more and more attentions.Percolation theory can be used to direct the research and development of composites with high dielectric constant. Percolation is a statistical concept that describes the formation of an infinite cluster of connected particles or pathways. The dielectric constant will increase singularly near the percolation threshold for composites made of an insulating matrix loaded with conductive or semiconducting particles. This gives interest for research of high permittivity composites.A series of novel composites, such as BaTiO₃-Acetylene black, BaTiO₃-NiO, BaTiO₃-Ni, BaTiO₃-Ni-Fe, BaTiO₃-Ni_0.5Zn_0.5Fe₂O₄, were created, and the microstructure and dielectric properties were investigated in this study.For the BaTiCVconductors composites, it is found that the introduction of conductors can enhance the dielectric constant obviously, and the percolation threshold depends on the shapes and sizes of fillers deeply.(1) For BaTiO₃-Acetylene black composites, the percolation threshold decreases with increasing temperature, as a result of the increase in density and the grain size of BaTi_O3. The introduction of acetylene black can enhance the dielectric constant obviously. A super high dielectric constant of about 40000 can be obtained in the composites, which is about 12 times more than that of BaTiO₃ without acetylene black doping. Moreover, the dielectric constant depends slightly on the temperature.(2) For BaTiO₃-Ni and BaTiO₃-Ni-Fe composites, it is found that the introduction of metal dilutes the internal stresses and leads to lower loss. Furthermore, the introduction of metal increases the dielectric constant observably. And it isnoticeable that the dielectric constant depends slightly on the temperature for composites near the percolation threshold due to the small grain size of BaTiO3.(3) The physical reason for the dielectric enhancement is the formation of a great deal of micro-capacitors as well as the induction of space charge polarization.For the BaTiO3-NiO composites, the results indicate that the Ni2+ ions might diffuse into BaTiO3 perovskite phase gradually during calcinations, and the perovskite phase of BaTiO3 consisted of different saturated solid solutions when sintering the composites at low temperature for a short time. The different composition of Ni2+ in the perovskite phase led to that the dielectric constant of the composite changed near the Curie point with temperature much more softly than that without doping Ni2+.For BaTi03-Nio.5Zno.5Fe204 composites, it is found that the percolation threshold is about 50 wt% NiojZno.sFeiO^ For composites near the percolation threshold, the permeability is about 10, and the dielectric constant reaches a maximal value of about 3000, while the dielectric loss remain as low as 0.10. This means that the BaTi03-Nio.5Zno.5Fe204 composites can have both high permittivity and excellent magnetism properties at the same time, which make for broadening the potential application of percolating composites with novel high dielectric constant.