The origin of giant dielectric relaxation and electrical responses of grains and grain boundaries of W-doped CaCu3Ti4O12 ceramics

Abstract

The origin of giant dielectric relaxation behavior and related electrical properties of grains and grain boundaries (GBs) of W6+-doped CaCu3Ti4O12 ceramics were studied using admittance and impedance spectroscopy analyses based on the brick–work layer model. Substitution of 1.0 at. % W6+ caused a slight decrease in GB capacitance, leading to a small decrease in the low-frequency dielectric constant. Surprisingly, W6+ doping ions have remarkable effects on the macroscopic dielectric relaxation and electrical properties of grains. X-ray photoelectron spectroscopy analysis suggested that the large enhancements of grain resistance and conduction activation energy of grains for the W6+-doped CaCu3Ti4O12 ceramic are caused by reductions in concentrations of Cu3+ and Ti3+ ions. Considering variation of dielectric properties together with changes in electrical properties of the W6+-doped CaCu3Ti4O12 ceramic, correlation between giant dielectric properties and electrical responses of grains and GBs can be described well by the internal barrier layer capacitor model. This model can ascribe mechanisms related to giant dielectric response and relaxation behavior in CaCu3Ti4O12 ceramics.

Effect of Annealing in O2 and Mechanisms Contributing to the Overall Loss Tangent of CaCu3Ti4O12 Ceramics

“…6,[15][16][17][18][19] Normally, most strategies selected to improve a particular dielectric property, e.g., to reduce tan d or enhance e¢, simultaneously worsen other important dielectric properties of these materials. 15,17,20 An increase in e¢ or strong reduction of tan d is generally accompanied by a strong increase in tan d or remarkable decrease in e¢, respectively; For example, 8 substitution of W 6+ into CCTO ceramics can reduce the low-frequency tan d value at room temperature. However, it enhanced the tan d value at high frequencies due to decrease of the frequency at which dielectric relaxation occurred.…”

“…This is because a relaxation process is usually accompanied by a strong increase in tan d near the relaxation peak. 3,6,8,[20][21][22][23][24][25] While studies to understand the mechanisms of unusually high dielectric responses have been carried out, [2][3][4][5][6][7][8]11,20,23,26 systematic investigation to understand the mechanisms of energy loss in CCTO ceramics has never been undertaken. This is another important issue needing investigation to realize the goal of application of CCTO ceramics.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] This is because many electronic technologies require high-permittivity dielectric material to fabricate small-sized multilayer ceramic capacitors with high energy storage density. Many interesting dielectric and electrical phenomena have been observed in CCTO, in both single-and polycrystalline ceramics.…”

Influence of interface point defect on the dielectric properties of Y doped CaCu3Ti4O12 ceramics

“…In the past several years, many models have been proposed to illustrate the origin of giant dielectric constant. [4][5][6][7] However, it is still questionable whether the high dielectric constant is intrinsic to a perfect crystal or extrinsic and related to the material microstructure (such as grain size) and processing conditions (such as sintering temperature and time, cooling rate, etc.). According to these models, the method for depressing dielectric loss could be found.…”

Dielectric properties and impedance characteristics of BaO–Cr2O3–Sb2O5 ceramics

“…6reveals the plots of In (s) versus 1000/T for the ceramic sintered at 1280°C. The activation energy of dielectric relaxation can be modified by the following relationship[22,23]:…”