Enhancement of dielectric properties by additions of Ni nano-particles to a X7R-type barium titanate ceramic matrix

Some different amounts of nano-sized Ni powder (from 1 to 30 vol.%) have been mixed with BaTiO3-based EIA X7R ceramic powders used in base metal electrode (BME) multilayer ceramic capacitors (MLCC). The X-ray diffraction (XRD) analysis indicated that no phases other than BaTiO3 and Ni were present in the doped ceramics and further suggested that no reaction took place between BaTiO3 and Ni during sintering under reducing atmosphere. The scanning electronic microscope (SEM) observation showed that the Ni particles presented homogeneous distribution in BaTiO3 ceramic matrix. It was found that the relative density decreased with increasing Ni-content while the dielectric constant at broad temperature range increased. The dielectric constant at room temperature of the ceramic with Ni-content of 28 vol.% is about 6000, 2.5 times of Ni-free ceramics, 2500. When Ni-content is 30%, the ceramic became a conductor. The temperature coefficient of capacitors (TCC) of the ceramics showed decline with the increase of Ni-content. The percolation theory of insulator–metal transitions can explain the enhancement of dielectric constant. The percolation threshold of the ceramic–metal composites for dielectric constants at room temperature, fc, is 37 vol.% and the critical exponent, p, is 0.6. The dielectric losses, tgδ showed the similar phenomena with ε.