Dielectric Relaxationand Giant Dielectric Constantrnof Nb-doped Cacu_3ti_4o_(12)ceramics Under Dc Bias Voltage

摘要

CaCu_3Ti_(4-x)Nb_xO_(12) (x = 0, 0.01, 0.08, 0.2) ceramics were fabricated by a conventional solid-state reaction method. The ceramics showed the body-centered cubic structure without any foreign phases and the grain size decreases with Nb doping. Two Debye-type relaxations were observed for the Nb-doped samples at low frequency and high frequency, respectively. The complex electric modulus analysis revealed that the surface layer, grains and grain boundaries contributed to the di-rnelectric constant. The low-frequency dielectric constant relative to the surface layer decreased to a minimum and then increased with the dc bias voltage at 100 Hz, which were well explained in terms of a model containing two metal oxide semiconductors in series, confirming the surface layer in the ceramics. The shift voltage V_B corresponding to the minimal capacitance increased with increase of the composition x.