Non‐Ohmic Properties and Electrical Responses of Grains and Grain Boundaries of Na_1/2Y_1/2Cu₃Ti₄O₁₂ Ceramics

Abstract

The dielectric and non‐Ohmic properties of Na1/2Y1/2Cu3Ti4O12 ceramics sintered under various conditions to obtain different microstructures were investigated. Microstructure analysis confirmed the presence of Na, Y, Cu, Ti, and O and these elements were well dispersed in the microstructure. Na1/2Y1/2Cu3Ti4O12 ceramics exhibited non‐Ohmic characteristics with large nonlinear coefficients of about 5.7–6.6 irrespectively of sintering conditions. The breakdown electric field of fine‐grained ceramic with the mean grain size of ≈1.7 μm (≈5600 V/cm) was much larger than those of the course‐grained ceramics with grain sizes of ≈9.5–10.4 μm (≈1850–2180 V/cm). Through optimization of sintering conditions, a low loss tangent of about 0.03 and very high dielectric permittivities of 18 000–23 000 with good temperature stability were successfully accomplished. The electrical responses of the grains and grain boundaries can, respectively, be well described using admittance and impedance spectroscopy analyses based on the brickwork layer model. A possible mechanism for the origin of semiconducting grains is discussed. The colossal dielectric response was reasonably described as closely correlated with the electrically heterogeneous microstructure by means of strong interfacial polarization at the insulating grain‐boundary layers. The non‐Ohmic properties of Na1/2Y1/2Cu3Ti4O12 ceramics were primarily related to their microstructure, i.e., grain size and volume fraction of grain boundaries.

Grain boundary engineering that induces ultrahigh permittivity and decreased dielectric loss in CdCu3Ti4O12 ceramics

“…Here, the activation energy E gb is physically understood to be the potential barrier height at the grain boundaries . These E gb values of the CdCu 3− x Zn x Ti 4 O 12 ceramics ( E gb ~ 0.75‐0.85 eV) are comparable to those reported for other ACTO‐type ceramics . According to the IBLC model, double Schottky barriers from n ‐type grains to insulating grain boundaries, and vice versa, can form.…”

“…Indeed, the radii of the semicircles decrease with increasing temperature, confirming that the resistivity of the grain boundaries is inversely proportional to temperature, which is a typical behavior of degenerate semiconductors. According to the temperature dependence of the resistivity, the activation energy E gb can be calculated by the Arrhenius law:where σ 0 is the pre‐exponential temperature‐dependent constant, k B is the Boltzmann constant, and T is the absolute temperature. A linear fitting of ln σ gb vs 1000/ T provides E gb , as displayed in the inset.…”

“…12,33,45 These E gb values of the CdCu 3−x Zn x Ti 4 O 12 ceramics (E gb ~ 0.75-0.85 eV) are comparable to those reported for other ACTO-type ceramics. [15][16][17][18]46,47 According to the IBLC model, double Schottky barriers from n-type grains to insulating grain boundaries, and vice versa, can form. Without a dc bias, the Schottky barrier height Φ gb can be expressed as follows 34,45,[48][49][50] : where q is the electronic charge, N d is the charge carrier concentration, and N s is the density of the interface states.…”

“…The search for ultrahigh permittivity ( ε r > 10 3 ) materials is one of the most popular research topics in the fields of microelectronics and energy storage devices . CaCu 3 Ti 4 O 12 (CCTO), a typical ACu 3 Ti 4 O 12 (ACTO, where A = Ca, Cd, La 2/3 , Y 2/3 , Bi 2/3 , Na 1/2 La 1/2 , Na 1/2 Y 1/2 , or Na 1/2 Bi 1/2 , for example) ceramic, has been widely studied due to its ultrahigh dielectric permittivity and good frequency/thermal stability. However, other members of the ACTO family with isostructures have rarely been studied.…”

Microstructural evolution, non‐Ohmic properties, and giant dielectric response in CaCu3Ti4−xGexO12 ceramics

“…R gb values at different temperatures could be obtained. According to our previous work, R g can easily be calculated from the frequency dependence of Y ″, the imaginary part of admittance complex (Y*). R g ≈ 1/2 Y ″ max , where Y ″ max is the maximum value at the Y″ ‐peak.…”