Giant dielectric response, nonlinear characteristics, and humidity sensing properties of a novel perovskite: Na1/3Sr1/3Tb1/3Cu3Ti4O12.

In this study, we unveil a novel perovskite compound, Na1/3Sr1/3Tb1/3Cu3Ti4O12, synthesized through a solid-state reaction method, exhibiting remarkable giant dielectric response, nonlinear characteristics, and humidity sensing capabilities. This research highlights the emergence of a Cu-rich phase, the properties of which undergo significant alterations depending on the sintering conditions. The optimization of sintering parameters, encompassing a temperature range of 1040-1450 °C for 1-8 h, resulted in substantial dielectric permittivity (ε') values (∼2800-6000). The temperature dependence of ε' demonstrated relationship to the particular sintering conditions utilized. The acquired loss tangent values were situated within encouraging values, ranging from 0.06 to 0.16 at 1 kHz. Furthermore, the material revealed distinct nonlinear electrical characteristics at 25 °C, with the nonlinear coefficient values of 5-127, depending on ceramic microstructures. Additionally, we delved deeply into the humidity-sensing properties of the Na1/3Sr1/3Tb1/3Cu3Ti4O12 material, showing a considerable variation in ε' in response to fluctuations in relative humidity, thereby indicating its prospective application in humidity sensing technologies. The hysteresis error and response/recovery times were calculated, highlighting the versatility of this compound and its promising potential across multiple applications. The Na1/3Sr1/3Tb1/3Cu3Ti4O12 not only shows remarkable giant dielectric responses but also portrays significant promise for nonlinear and humidity sensing applications, marking it as a significant participant in the advancement of perovskite-based functional materials.

Significantly improved giant dielectric properties and enhanced nonlinear coefficient of Ni2+ doped CaCu3Ti4O12/CaTiO3 composites.

CaCu3-xNixTi4O12/CaTiO3 ceramic composites were fabricated using initial Ca2Cu2-xNixTi4O12 compositions (x = 0, 0.05, 0.10, and 0.20) to improve the dielectric properties (DPs) of the CaCu3Ti4O12 ceramics. CaCu3Ti4O12 and CaTiO3 phases were confirmed. Microstructural analysis and Rietveld refinement showed that the Ni2+ dopant might substitute the Cu2+ sites of the CaCu3Ti4O12 structure. The average grain sizes of CaCu3Ti4O12 (4.1-5.6 µm) and CaTiO3 (1.2-1.4 µm) changed slightly with the Ni2+ doping concentration. The best DPs were obtained for the CaCu3-xNixTi4O12/CaTiO3 with x = 0.2. The loss tangent was significantly reduced by an order of magnitude compared to that of the undoped composite, from tanδ∼0.161 to ∼0.016 at 1 kHz, while the dielectric permittivity slightly decreased from ε'∼5.7 × 103 to ∼4.0 × 103. Furthermore, the temperature dependence of ε' could be improved by doping with Ni2+. The improved DPs were caused by the enhanced electrical responses of the internal interfaces, which resulted in enhanced non-Ohmic properties. The largest nonlinear coefficient (α∼7.6) was obtained for the CaCu3-xNixTi4O12/CaTiO3 with x = 0.05. Impedance spectroscopy showed that the CaCu3-xNixTi4O12/CaTiO3 composites consisted of semiconducting and insulating components. The DPs of CaCu3-xNixTi4O12/CaTiO3 were explained based on the space-charge polarization at the active-interfaces.

Effects of sintering condition on giant dielectric and nonlinear current-voltage properties of Na1/2Y1/2Cu3Ti3.975Ta0.025O12 ceramics.

The effects of sintering conditions on the microstructure, giant dielectric response, and electrical properties of Na1/2Y1/2Cu3Ti3.975Ta0.025O12 (NYCTTaO) were studied. A single phase of Na1/2Y1/2Cu3Ti4O12 and a high density (>98.5%) were obtained in the sintered NYCTTaO ceramics. First-principles calculations were used to study the structure of the NYCTTaO. Insulating grain boundaries (i-GBs) and semiconducting grains (semi-Gs) were studied at different temperatures using impedance and admittance spectroscopies. The conduction activation energies of the semi-Gs and i-GBs were Eg ≈ 0.1 and Egb ≈ 0.6 eV, respectively. A large dielectric constant (ε' ≈ 2.43-3.89 × 104) and low loss tangent (tanδ ≈ 0.046-0.021) were achieved. When the sintering temperature was increased from 1070 to 1090 °C, the mean grain size slightly increased, while ε' showed the opposite tendency. Furthermore, the breakdown electric field (Eb) increases significantly. As the sintering time increased from 5 to 10 h, the mean grain size did not change, whereas ε' and Eb increased. Variations in the dielectric response and non-linear electrical properties were primarily described by the intrinsic (Egb) and extrinsic (segregation of Na-, Cu-, Ta-, and O-rich phases) properties of the i-GBs based on the internal barrier layer capacitor effect.

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

In this work, the colossal dielectric properties and Maxwell-Wagner relaxation of TiO2-rich Na1/2Y1/2Cu3Ti4+xO12 (x = 0-0.2) ceramics prepared by a solid-state reaction method are investigated. A single phase of Na1/2Y1/2Cu3Ti4O12 is achieved without the detection of any impurity phase. The highly dense microstructure is obtained, and the mean grain size is significantly reduced by a factor of 10 by increasing Ti molar ratio, resulting in an increased grain boundary density and hence grain boundary resistance (Rgb). The colossal permittivities of ε' ~ 0.7-1.4 × 104 with slightly dependent on frequency in the frequency range of 102-106 Hz are obtained in the TiO2-rich Na1/2Y1/2Cu3Ti4+xO12 ceramics, while the dielectric loss tangent is reduced to tanδ ~ 0.016-0.020 at 1 kHz due to the increased Rgb. The semiconducting grain resistance (Rg) of the Na1/2Y1/2Cu3Ti4+xO12 ceramics increases with increasing x, corresponding to the decrease in Cu+/Cu2+ ratio. The nonlinear electrical properties of the TiO2-rich Na1/2Y1/2Cu3Ti4+xO12 ceramics can also be improved. The colossal dielectric and nonlinear electrical properties of the TiO2-rich Na1/2Y1/2Cu3Ti4+xO12 ceramics are explained by the Maxwell-Wagner relaxation model based on the formation of the Schottky barrier at the grain boundary.

Influences of Sr2+ Doping on Microstructure, Giant Dielectric Behavior, and Non-Ohmic Properties of CaCu3Ti4O12/CaTiO3 Ceramic Composites.

The microstructure, dielectric response, and nonlinear current-voltage properties of Sr2+-doped CaCu3Ti4O12/CaTiO3 (CCTO/CTO) ceramic composites, which were prepared by a solid-state reaction method using a single step from the starting nominal composition of CCTO/CTO/xSrO, were investigated. The CCTO and CTO phases were detected in the X-ray diffraction patterns. The lattice parameter increased with increasing Sr2+ doping concentration. The phase compositions of CCTO and CTO were confirmed by energy-dispersive X-ray spectroscopy with elemental mapping in the sintered ceramics. It can be confirmed that most of the Sr2+ ions substituted into the CTO phase, while some minor portion substituted into the CCTO phase. Furthermore, small segregation of Cu-rich was observed along the grain boundaries. The dielectric permittivity of the CCTO/CTO composite slightly decreased by doping with Sr2+, while the loss tangent was greatly reduced. Furthermore, the dielectric properties in a high-temperature range of the Sr2+-doped CCTO/CTO ceramic composites can be improved. Interestingly, the nonlinear electrical properties of the Sr2+-doped CCTO/CTO ceramic composites were significantly enhanced. The improved dielectric and nonlinear electrical properties of the Sr2+-doped CCTO/CTO ceramic composites were explained by the enhancement of the electrical properties of the internal interfaces.

Dramatically enhanced non-Ohmic properties and maximum stored energy density in ceramic-metal nanocomposites: CaCu3Ti4O12/Au nanoparticles.

Non-Ohmic and dielectric properties of a novel CaCu3Ti4O12/Au nanocomposite were investigated. Introduction of 2.5 vol.% Au nanoparticles in CaCu3Ti4O12 ceramics significantly reduced the loss tangent while its dielectric permittivity remained unchanged. The non-Ohmic properties of CaCu3Ti4O12/Au (2.5 vol.%) were dramatically improved. A nonlinear coefficient of ≈ 17.7 and breakdown electric field strength of 1.25 × 104 V/m were observed. The maximum stored energy density was found to be 25.8 kJ/m3, which is higher than that of pure CaCu3Ti4O12 by a factor of 8. Au addition at higher concentrations resulted in degradation of dielectric and non-Ohmic properties, which is described well by percolation theory.