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1.
Prasit Thongbai Jutapol Jumpatam Teerapon Yamwong Santi Maensiri 《Journal of the European Ceramic Society》2012,32(10):2423-2430
The effects of Ta5+ substitution on the microstructure, electrical response of grain boundary, and dielectric properties of CaCu3Ti4O12 ceramics were investigated. The mean grain size decreased with increasing Ta5+ concentration, which was ascribed to the ability of Ta5+ doping to inhibit grain boundary mobility. This can decrease dielectric constant values. Grain boundary resistance and potential barrier height of CaCu3Ti4O12 ceramics were reduced by doping with Ta5+. This results in enhancement of dc conductivity and the related loss tangent. Influence of charge compensations on microstructure and intrinsic electrical properties of grain boundaries resulting from the effects of replacing Ti4+ with Ta5+ are discussed. The experimental data and variation caused by the substitution of Ta5+ can be described well by the internal barrier layer capacitor model based on space charge polarization at the grain boundaries. 相似文献
2.
Jutapol Jumpatam Bundit Putasaeng Teerapon Yamwong Prasit Thongbai Santi Maensiri 《Ceramics International》2013,39(2):1057-1064
The influences of Ga3+ doping ions on the microstructure, dielectric and electrical properties of CaCu3Ti4O12 ceramics were investigated systematically. Addition of Ga3+ ions can cause a great increase in the mean grain size of CaCu3Ti4O12 ceramics. This is ascribed to the ability of Ga3+ doping to enhance grain boundary mobility. Doping CaCu3Ti4O12 with 0.25 mol% of Ga3+ caused a large increase in its dielectric constant from 5439 to 31,331. The loss tangent decreased from 0.153 to 0.044. The giant dielectric response and dielectric relaxation behavior can be well described by the internal barrier layer capacitor model based on Maxwell?Wagner polarization at grain boundaries. The nonlinear coefficient, breakdown field, and electrostatic potential barrier at grain boundaries decreased with increasing Ga3+ content. Our results demonstrated the importance of ceramic microstructure and electrical responses of grain and grain boundaries in controlling the giant dielectric response and dielectric relaxation behavior of CaCu3Ti4O12 ceramics. 相似文献
3.
Jing Wang Zhenya Lu Tengfei Deng Caifu Zhong Zhiwu Chen 《Journal of the European Ceramic Society》2018,38(10):3505-3511
The dielectric properties and voltage–current nonlinearity of the pure and various cobalt-doped CaCu3Ti4O12 (Co-doped CCTO) prepared by solid-state reactions were investigated. The improved dielectric properties in the Co-doped CCTO, with a dielectric constant ≈7.4?×?104 and dielectric loss ?≈?0.034, were observed in the sample with a Co doping of 5% (CCTO05) at room temperature and 1?kHz. The related multi-relaxations, RII (?20 to 40?°C) and RIII (100–150?°C), were demonstrated to be a Debye-like relaxation and a Maxwell–Wagner relaxation related to oxygen vacancies. The low dielectric loss of CCTO05 was associated with the high grain boundary resistance and the increase in cation vacancies. The improved nonlinear electrical properties (CCTO05, with nonlinear coefficients ?≈?5.22 and breakdown electric field ?≈?300.46?V/cm) and the ferromagnetism in Co-doped CCTO were also discussed. 相似文献
4.
《Ceramics International》2022,48(16):23428-23435
CaCu3Ti4O12-xwt%BiSbO4 ceramics (CCTO-xwt%BSO, x = 0, 1, 2, 3) were prepared by solid-state reaction method. The microstructure, dielectric properties, varistor properties, photoluminescence properties of CCTO-xwt%BSO ceramics were studied in this work. Results showed that all samples formed CaCu3Ti4O12 (CCTO) single phase. Doping BiSbO4 (BSO) restrained the abnormal grain growth and increased the grain boundary density of ceramics. The introduction of BSO led to the increase of the grain boundary resistance, reducing the dielectric loss and enhancing the temperature stability of dielectric properties. The nonlinear electrical characteristics are enhanced with proper concentration of BSO. And the improved varistor performance with breakdown electric field of ~3.98–34.6 and nonlinear coefficient of ~1.49–2.96 are obtained for CCTO-xwt%BSO samples. In addition, the photoluminescent emission of the samples is enhanced with the addition of appropriate equivalent BSO, showing the potential applications in novel devices with photoluminescent/electrical multifunctional properties. 相似文献
5.
《Journal of the European Ceramic Society》2007,27(13-15):3991-3995
The abnormal grain growth (AGG) behavior of undoped and SiO2-doped CaCu3Ti4O12 (CCTO) ceramics were investigated. With the addition of 2 wt.% SiO2, the AGG-triggering temperature decreased from 1100 to 1060 °C, and the temperature for obtaining a uniform and coarse microstructure decreased from 1140 to 1100 °C. The lowering of the AGG temperature by SiO2 addition was attributed to the formation of a CuO-SiO2-rich intergranular phase at lower temperature. The apparent dielectric permittivity of coarse SiO2-doped CCTO ceramics was ∼10 times higher than that of fine SiO2-doped CCTO ceramics at the frequency of 103–105 Hz. The doping of SiO2 to CCTO ceramics provides an efficient route of improving the dielectric properties via grain coarsening. The correlation between the microstructure and apparent permittivity suggests the presence of a barrier layer near the grain boundary. 相似文献
6.
The effects of Sm substitution on structure, dielectric properties and conductivity of CaCu3Ti4O12 ceramics were investigated. Ca1?xSmxCu3Ti4O12 (x=0.0%, 0.5%, 1.0%) ceramics were synthesized by the solid-state reaction method. Single phase crystal of the ceramics with space group Im3 was obtained. With increasing Sm content, the dielectric loss of Ca1?xSmxCu3Ti4O12 ceramics improved but the dielectric constant also decreased significantly, with both the low- and high-temperature dielectric relaxations suppressed. 相似文献
7.
《Ceramics International》2019,45(12):15082-15090
The formation and compositions of grain boundary layers are very important factors to improve the electrical properties of CaCu3Ti4O12 (CCTO) ceramics. In present work, the dielectric and nonlinear properties of the CCTO ceramics are enhanced by controlling the Cu-rich phase degree at grain boundary layers. The dense CCTO ceramics were prepared successfully through mixing the nanometer and micrometer powders and using the cold isostatic pressing process. The average grain size of these CCTO ceramics is about 30.71(±11.76) ∼ 62.01(±32.16) μm, and their grain microstructures show the Cu-rich phases at grain boundary layers. The CCTO ceramics with the mass ratios of nanometer and micrometer powders 7:3 display a giant dielectric constant of 5.4 × 104, low dielectric loss of 0.048 at 103 Hz, enhanced nonlinear coefficients of 11.12, as well as the noteworthy breakdown field of 4466.17 V/cm. The complex impedance spectroscopy results indicate that the giant dielectric behavior is due to the electrically heterogeneous grain/grain boundary characteristics from internal barrier layer capacitance (IBLC) model. The lower dielectric loss and the higher breakdown field are attributed to the high resistance grain boundary layers with the Cu-rich phase. The improved nonlinear properties are related to the increased Schottky barrier height at grain boundary. This work may provide a potential way to design the CCTO ceramics with excellent electrical properties from the viewpoint of controlling the response of the Cu-rich phase grain boundary. 相似文献
8.
Jakkree Boonlakhorn Narong Chanlek Jedsada Manyam Sriprajak Krongsuk Prasit Thongbai Pornjuk Srepusharawoot 《Ceramics International》2021,47(16):22390-22396
CaCu3-xZnxTi4O12 ceramics (x = 0, 0.05, 0.10) were successfully prepared by a conventional solid-state reaction method. Their structural and dielectric properties, and nonlinear electrical response were systematically inspected. The X-ray diffraction results indicated that single-phase CaCu3Ti4O12 (JCPDS no. 75–2188) was obtained in all sintered ceramics. Changes in the lattice parameter are well-matched with the computational result, indicating an occupation of Zn2+ doping ions at Cu2+ sites. The overall tendency shows that the average grain size decreases when x increases. Due to a decrease in overall grain size, the dielectric permittivity of CaCu3-xZnxTi4O12 decreases expressively. Despite a decrease in the dielectric permittivity, it remains at a high level in the doped ceramics (~3,406–11,441). Besides retention in high dielectric permittivity, the dielectric loss tangent of x = 0.05 and 0.10 (~0.074–0.076) is lower than that of x = 0 (~0.227). A reduction in the dielectric loss tangent in the CaCu3-xZnxTi4O12 ceramics is closely associated with the enhanced grain boundary response. Increases in grain boundary resistance, breakdown electric field, and conduction activation energy of grain boundary as a result of Zn2+ substitution are shown to play a crucial role in improved grain boundary response. Furthermore, the XPS analysis shows the existence of Cu+/Cu2+ and Ti3+/Ti4+, indicating charge compensation due to the loss of oxygen lattice. Based on all results of this work, enhanced dielectric properties of the Zn-doped CCTO can be explained using the internal barrier layer capacitor model. 相似文献
9.
CaxCu3Ti4O12 (x = 0.90, 0.97, 1.0, 1.1 and 1.15) polycrystalline powders with variation in calcium content were prepared via the oxalate precursor route. The structural, morphological and dielectric properties of the ceramics fabricated using these powders were studied using X-ray diffraction, scanning electron microscope along with energy dispersive X-ray analysis, transmission electron microscopy, electron spin resonance (ESR) spectroscopy and impedance analyzer. The X-ray diffraction patterns obtained for the x = 0.97, 1.0 and 1.1 powdered ceramics could be indexed to a body-centered cubic perovskite related structure associated with the space group Im3. The ESR studies confirmed the absence of oxygen vacancies in the ceramics that were prepared using the oxalate precursor route. The dielectric properties of these suggest that the calcium deficient sample (x = 0.97) has a reduced dielectric loss while retaining the high dielectric constant which is of significant industrial relevance. 相似文献
10.
《Journal of the European Ceramic Society》2020,40(6):2375-2381
CaCu3Ti4O12 (CCTO) has been reported to possess a colossal dielectric constant owing to the intrinsic interfacial polarization via charge accumulations across the grain boundary. Herein, we explore the effects of unusual anion-doping on the dielectric properties of sputter-deposited CCTO thin films using an example of sulfur-doping. A post-annealing process of the films was utilized in a flowing H2S atmosphere for the sulfur-doping. The incorporation of sulfur into the perovskite structure was evidenced with the changes in chemical states, such as the reduced cations of Cu+ and Ti3+, the increased concentration of oxygen vacancies, and the formation of S-O bonds. The sulfurized CCTO thin films demonstrated an enhanced relative permittivity of ∼620 at 100 Hz, which is substantially better than that of the unsulfurized film. Direct measurement of the grain-boundary potential using Kelvin probe force microscopy suggests that the enhanced relative permittivity is associated with an increased Schottky barrier height. 相似文献
11.
《Ceramics International》2016,42(10):12005-12009
The effects of small amounts of lithium fluoride sintering aid on the microstructure and dielectric properties of CaCu3Ti4O12 (CCTO) ceramics were investigated. CCTO polycrystalline ceramics with 0.5 and 1.0 mol% LiF, and without additive were prepared by solid state synthesis. Good densification (>90% of the theoretical density) was obtained for all prepared materials. Specimens without the sintering aid and sintered at 1090 °C exhibit secondary phases as an outcome of the decomposition reaction. The mean grain size is controlled by the amount of LiF in specimens containing the additive. Impedance spectroscopy measurements on CaCu3Ti4O12 ceramics evidence the electrically heterogeneous nature of this material consisting of semiconductor grains along with insulating grain boundaries. The activation energy for grain boundary conduction is lower for specimens prepared with the additive, and the electric permittivity reached 53,000 for 0.5 mol% LiF containing CCTO. 相似文献
12.
《Journal of the European Ceramic Society》2006,26(7):1245-1257
A “soft chemistry” method, the coprecipitation, has been used to synthesize the perovskite CaCu3Ti4O12 (CCT). Three main types of materials were obtained for both powders and sintered ceramics: a monophased consisting of the pure CCT phase, a biphased (CCT + CaTiO3), and a three-phased (CCT + CaTiO3 + copper oxide (CuO or Cu2O)). These ceramics, sintered at low temperature, 1050 °C, present original dielectric properties. The relative permittivity determined in the temperature range (−150 < T < 250 °C) is significantly higher than the one reported in the literature. Internal barrier layer capacitor is the probable mechanism to explain the particular behaviour. Moreover, the presence of a copper oxide phase beside the perovksite CCT plays an important role for enhancing the dielectric properties. 相似文献
13.
CaCu3-xNixTi4O12 (x?=?0, 0.05, and 0.10) powders were synthesized using a solid state reaction method. Phase structure and microstructure analyses revealed that all sintered CaCu3-xNixTi4O12 ceramics were of a pure phase. The CaCu3Ti4O12 ceramics had a dense microstructure and grain sizes were enlarged by doping with Ni2+. Interestingly, the dielectric permittivity was significantly enhanced, whereas the loss tangent was greatly suppressed to ~0.046–0.034 at 1?kHz. All sintered ceramics exhibited non-Ohmic characteristics. Clarification of the influences of DC bias showed that the dielectric permittivity and loss tangent values were increased by DC bias. The resistance of grain boundaries and the associated conduction activation energy of CaCu3-xNixTi4O12 ceramics were reduced as the DC bias voltage increased. Therefore, the observed non-Ohmic behavior and significantly enhanced dielectric properties should be closely related to variation in the Schottky barriers at the grain boundaries. 相似文献
14.
Effect of Gd on microstructural, dielectric and electrical properties has been studied over wide temperature (300–500 K) and frequency range (100 Hz–1 MHz). Gd substitution in CCTO system results in decrease in the grain size and increase of Schottky potential barrier which causes lower value of dielectric constant. The dielectric constant remains nearly constant in temperature range 300–350 K. Doped samples show lower dielectric loss in middle frequency range (~10 kHz–1 MHz) at room temperature. The AC conductivity (σac) obeys a power law, σac = Afn, where n is temperature dependent frequency exponent. The AC conductivity behaviour can be divided into three regions depending on conduction processes and the relevant charge transport mechanisms have been discussed. 相似文献
15.
Worawut Makcharoen Jerapong Tontrakoon Gobwute Rujijanagul David P. Cann Tawee Tunkasiri 《Ceramics International》2012
In this study, CaCu3Ti4O12 (CCTO) ceramics were doped with cesium and cerium atoms to possibly improve the electrical properties of these widely used ceramics. In all cases, pure phase perovskites were produced where cesium doping enhanced the grain growth and cerium doping produced grain growth inhibition. The cesium doping showed an improvement in loss tangent performance, in contrast to the cerium doping which showed a negative result. A high dielectric constant >15,000 with a dielectric loss lower than 0.06 was observed for cesium 2.0 mol% doped at high frequencies. These results were related to the change in microstructure and the properties of grain boundary after doping. 相似文献
16.
Maria Virginia Gelfuso Juan Oswaldo Montoya Uribe Daniel Thomazini 《International Journal of Applied Ceramic Technology》2019,16(2):868-882
The influence of the CuO–TiO2 phase (CT) on dielectric properties of the CCTO ceramic was investigated. CaCuXTiYO12 (CCXTYO) powders were prepared based on the coprecipitated method, where 2.70 ≤ x ≤ 3.30 and 3.25 ≤ y ≤ 4.75. XRD patterns confirmed the presence of CCTO and also the secondary phases as CuO, TiO2, and CaTiO3 for each sample and aided in its quantification. Scanning Electron Microscopy (SEM) shows secondary phases evolution in the grain boundaries, and its influence on size and morphology of the grains. Impedance spectroscopy measurements showed that the ceramics with lower amount of CuO and TiO2 phases (CT/deficient ceramics) exhibited the highest ε′ values (2.1 × 104 at 1 kHz for CC2.9T3.75O ceramic). Also, CT/deficient ceramics showed lower tanδ values (0.090 at 1 kHz for CC2.9T3.75O ceramic) than ceramics prepared with excessive CuO–TiO2 phase (0.241 at 1 kHz for CC3.1T4.25O ceramics). The deficiency of CuO and TiO2 phases associated with high percentage of CCTO and CaTiO3 phases resulted in ceramics with the higher ε′ values. 相似文献
17.
《Ceramics International》2019,45(11):14305-14311
Polycrystalline Ca1-xSrxCu3Ti4O12 ceramics were studied as a function of the strontium content in order to understand its effects on the structure, microstructure and electrical characteristics of these compounds. Our results showed that the Sr2+ cationic substitution into the A sites of the initial CaCu3Ti4O12 (CCTO) phase leads to crystalline phases with specific stoichiometry. Although the same space group is observed, the cationic substitution induces larger lattice parameter, phase density, and chemical bonding length when compared to the initial CCTO phase. Microstructure results indicated that the strontium content has a significant influence on sample sinterability leading to changes in grain growth and densification process. The non-ohmic characterization showed that the Ca0.5Sr0.5Cu3Ti4O12 phase exhibits improved breakdown electric field (32 kV/cm), non-linear coefficient (269) and lower leakage current (26 μA), while the SrCu3Ti4O12 phase presents permittivity of about 5000 at 1 kHz. 相似文献
18.
Microstructural evolution,non‐Ohmic properties,and giant dielectric response in CaCu3Ti4−xGexO12 ceramics 下载免费PDF全文
Jakkree Boonlakhorn Prasit Thongbai Bundit Putasaeng Pinit Kidkhunthod Santi Maensiri Prinya Chindaprasirt 《Journal of the American Ceramic Society》2017,100(8):3478-3487
The microstructural evolution, non‐Ohmic properties, and giant dielectric properties of CaCu3Ti4?xGexO12 ceramics (x=0‐0.10) are systematically investigated. The Rietveld refinement confirms the existence of a pure CaCu3Ti4O12 phase in all samples. Significantly enlarged grain sizes of CaCu3Ti4?xGexO12 ceramics are associated with the liquid phase sintering mechanism. Enhanced dielectric permittivity from 6.90×104 to 1.08×105 can be achieved by increasing Ge4+ dopant from x=0‐0.10, whereas the loss tangent is remarkably reduced by a factor of ≈10. Non‐Ohmic properties are enhanced by Ge4+ doping ions. Using impedance and admittance spectroscopies, the underlying mechanisms for the dielectric and nonlinear properties are well described. The improved nonlinear properties and reduced loss tangent are attributed to the enhanced resistance and conduction activation energy of the grain boundaries. The largely enhanced permittivity is closely associated with the enlarged grain sizes and the increase in the Cu+/Cu2+ and Ti3+/Ti4+ ratios, which are calculated from the X‐ray absorption near‐edge structure. 相似文献
19.
《Journal of the European Ceramic Society》2017,37(15):4653-4659
Different doping elements have been used to reduce the dielectric losses of CaCu3Ti4O12 ceramics, but their dielectric constants usually are undesirably decreased. This work intends to reduce their dielectric losses and simultaneously enhance their dielectric constants by co-doping Y3+ as a donor at A site and Al3+ as an acceptor at B site for substituting Ca2+ and Ti4+, respectively. Samples with different doping concentrations x = 0, 0.01, 0.02, 0.03, 0.05 and 0.07 have been prepared. It has been shown that their dielectric losses are generally reduced and their dielectric constants are simultaneously enhanced across the frequency range up to 1 MHz. The doped sample with x = 0.05 exhibits the highest dielectric constant, which is well over 104 for frequency up to 1 MHz and is about 20% higher than the undoped sample. Impedance spectra indicate that the doped samples have much higher grain boundary resistance than the undoped one. 相似文献
20.
《Journal of the European Ceramic Society》2007,27(13-15):3901-3905
In this work a comparative study of undoped CaCu3Ti4O12 (CCTO) and doped with Fe3+(CCTOF) and Nb5+(CCTON) ceramics, was aimed to modify the electronic transport. XRD patterns, FE-SEM microstructural analysis, impedance spectroscopy and I–V response curves were afforded to correlate the microstructure with the nonlinear I–V behaviour. The appearance of nonlinear behaviour in doped CCTO samples has been correlated with the ceramic microstructure that consists in n-type semiconductor grains, surrounded by a grain boundary phase based on CuO. The presence of this secondary grain boundary phase is the responsible of the assisted liquid phase sintering in CCTO ceramics. Doped samples showed cleaner grain boundaries than CCTO and nonlinearity in the I–V response. 相似文献