Effects of Charge Compensation on Colossal Permittivity and Electrical Properties of Grain Boundary of CaCu3Ti4O12 Ceramics Substituted by Al3+ and Ta5+/Nb5+

Abstract

The effects of charge compensation on dielectric and electrical properties of CaCu3Ti4-x(Al1/2Ta1/4Nb1/4)xO12 ceramics (x = 0−0.05) prepared by a solid-state reaction method were studied based on the configuration of defect dipoles. A single phase of CaCu3Ti4O12 was observed in all ceramics with a slight change in lattice parameters. The mean grain size of CaCu3Ti4-x(Al1/2Ta1/4Nb1/4)xO12 ceramics was slightly smaller than that of the undoped ceramic. The dielectric loss tangent can be reduced by a factor of 13 (tanδ ~0.017), while the dielectric permittivity was higher than 104 over a wide frequency range. Impedance spectroscopy showed that the significant decrease in tanδ was attributed to the highly increased resistance of the grain boundary by two orders of magnitude. The DFT calculation showed that the preferential sites of Al and Nb/Ta were closed together in the Ti sites, forming self-charge compensation, and resulting in the enhanced potential barrier height at the grain boundary. Therefore, the improved dielectric properties of CaCu3Ti4-x(Al1/2Ta1/4Nb1/4)xO12 ceramics associated with the enhanced electrical properties of grain boundaries. In addition, the non-Ohmic properties were also improved. Characterization of the grain boundaries under a DC bias showed the reduction of potential barrier height at the grain boundary. The overall results indicated that the origin of the colossal dielectric properties was caused by the internal barrier layer capacitor structure, in which the Schottky barriers at the grain boundaries were formed.

Significantly Improved Colossal Dielectric Properties and Maxwell—Wagner Relaxation of TiO2—Rich Na1/2Y1/2Cu3Ti4+xO12 Ceramics

“…Figure 4 a displays the Z* plots of all the ceramics at 30 °C. Only parts of the relatively large arcs can be observed with a nonzero intercept (inset of Figure 4 a), which is similar to that reported in the previous works [ 5 , 6 , 12 , 19 , 21 , 44 , 54 ]. The R g value at 30 °C, which can be calculated from the nonzero intercept, increases with increasing the excessive TiO 2 molar ratio.…”

“…However, the ε ′ of the NYCTO ceramic is largely dependent on the frequency in a low–frequency range, which is usually owing to the dominant effect of non–Ohmic sample–electrode interface [ 8 , 15 , 44 , 50 ]. At 10 6 Hz, the ε ′ begins to decline due to the primary dielectric relaxation mechanism [ 12 , 19 ]. Interestingly, the ε ′ values of the NYCTO + 0.1TiO 2 and NYCTO + 0.2TiO 2 ceramics are more stable with frequency than that of the NYCTO ceramic.…”

“…Furthermore, in this frequency range, the tanδ values of the NYCTO + 0.1TiO 2 and NYCTO + 0.2TiO 2 ceramics are lower than 0.1. The rapid increase in tanδ of all the ceramics is attributed to the primary dielectric relaxation, i.e., Maxwell—Wagner polarization relaxation [ 12 , 19 ]. The tanδ values of the NYCTO, NYCTO + 0.1TiO 2 and NYCTO + 0.2TiO 2 ceramics 10 3 Hz are 0.115, 0.020 and 0.016, respectively.…”

“…To improve the colossal dielectric and nonlinear J – E properties, many effective methods have been proposed and studied, such as doping with suitable ions [ 19 , 20 , 21 , 22 ], tuning ceramic microstructure [ 9 ] and fabricated CCTO–matrix composites [ 10 , 18 , 23 , 24 ]. These methods have the same approach, which is to increase the total resistance of the insulating GBs ( R gb ) for reducing tanδ.…”

Enhancing giant dielectric properties of Ta5+‐doped Na1/2Y1/2Cu3Ti4O12 ceramics by engineering grain and grain boundary

“…5 CCTO is a dielectric material exhibiting high ε′ (> 10 4 ) in the temperature range of 100-400 K. 5 The GDP in CCTO does not originate by the ferroelectricity, but rather by the internal barrier layer capacitor (IBLC) structure, consisting of semiconducting grains and insulating grain boundaries (GBs). [6][7][8][9][10][11][12][13][14] According to the presence of Schottky barrier height (SBH) at the GBs, the substitution of Acu 3 Ti 4 O 12 compounds with several doping ions has been used to improve dielectric and electrical properties via enhancement of the grain and GB properties. 9,10,[15][16][17] In the IBLC model, doping ions affect the microstructure, grain resistance grains (R g ), and GB resistance (R gb ), resulting in ε′ and tanδ variations over wide ranges of temperature and frequency.…”