Dielectric relaxations and low dissipation factor with excellent temperature stability of Ti1-x(Co1/3Ta2/3)xO2 ceramics

Abstract

Low dissipation factor (tanδ) and excellent temperature stability of high dielectric permittivity are obtained in Ti1-x(Co1/3Ta2/3)xO2 ceramics, which were prepared using a mixed oxide method. The unit cell of the rutile TiO2 structure expanded due to relatively larger ionic radii of the co–dopants. The dopants homogeneously appeared in the microstructure of the TiO2 ceramics. Highly dense sintered–ceramics without second phase exhibit low tanδ of 0.015–0.043 with very high dielectric permittivities of 7.0–9.1 × 104 at 1 kHz. Notably, the temperature coefficient in the range of ±15 % was obtained in the temperature range of −60–200 °C. The electrically heterogeneous microstructure was studied using impedance spectroscopy. The contributions of extrinsic and intrinsic factors were separated by the dielectric relaxations in low and high–frequency ranges, respectively. The dielectric relaxations were well fitted using a modified Cole-Cole model. A low–frequency relaxation was well described based on the Maxwell-Wagner relaxation model. A high permittivity was originated from the intrinsic (i.e., defect dipoles) and extrinsic (internal barrier layer capacitor, IBLC) effects. A low tanδ was primarily caused by the IBLC effect associated with a high resistance of the insulating part and defect dipoles.

Keywords

• Giant/Colossal permittivity
• Grain boundary barrier layer capacitor
• Impedance spectroscopy
• TiO2
• Temperature coefficient