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 BaTiO 3 -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 BaTiO 3 and Ni were present in the doped ceramics and further suggested that no reaction took place between BaTiO 3 and Ni during sintering under reducing atmosphere. The scanning electronic microscope (SEM) observation showed that the Ni particles presented homogeneous distribution in BaTiO 3 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, f c ,i s 37 vol.% and the critical exponent, p, is 0.6. The dielectric losses, tgδ showed the similar phenomena with e.