Co-doped CaCu3Ti4O12 Ceramics Research Articles

(Zn2+ + Cd2+) co-doped CaCu3Ti4O12 ceramics with enhanced dielectric permittivity and reduced dielectric loss tangent

The present study systematically investigated the structure, dielectric properties, and electrical response of Ca1-xCdxCu3-yZnyTi4O12 (x = y = 0, 0.025, 0.05, and 0.10). The XRD analysis indicates the presence of a CaCu3Ti4O12 phase in all the sintered ceramics, with no indications of impurity phases found. Achieving high dielectric permittivity and low loss tangent can be accomplished through codoping with Zn2+/Cd2+. At room temperature and 1 kHz, the Ca0.95Cd0.05Cu2.95Zn0.05Ti4O12 ceramic has a high dielectric constant of ∼1.61 × 105 and a low loss tangent of ∼0.03. In addition, codoping ions can enhance the stability of dielectric permittivity with respect to temperature variations. The utilization of impedance spectroscopy as a technique confirms the heterogeneous microstructure observed in sintered materials. The results of this investigation suggest a potential association between the internal barrier layer capacitor model and the underlying cause of the colossal dielectric characteristics observed in Ca1-xCdxCu3-yZnyTi4O12 materials. The analysis of X-ray photoelectron spectroscopy indicates the presence of Cu+ and Ti3+ species, which could potentially exert a significant impact on the development of n-type semiconducting grains in Ca1-xCdxCu3-yZnyTi4O12 ceramics. This influence is attributed to the existence of oxygen vacancies. Theoretical simulations revealed that a Zn atom is situated in proximity to a Cd atom within the CCTO structure. Furthermore, our findings indicate that the oxygen vacancy does not interact with the dopants. Our electron density analysis suggests that the presence of Cu+ and Ti3+ ions, as observed by XPS measurements, is a consequence of the existing oxygen vacancy.

Thermal behavior of La3+, Ni2+ and Sn4+ co-doped CaCu3Ti4O12 ceramics dielectric response

Dielectric properties control by elements co-doping is important research problem for application of ceramics based on CaCu3Ti4O12 (CCTO) as a component of electronic devices. In this work, the effect of La3+, Ni2+ and Sn4+ co-doping on the dielectric properties of CCTO ceramics, including their thermal stability, was investigated. Solid solutions with compositions of Ca1-xLa2x/3Cu2.95Ni0.05Ti3.7Sn0.3O12 (x = 0.010–0.055), Ca0.94La0.027Cu3-yNiyTi3.7Sn0.3O12 (y = 0.020–0.065), Ca0.94La0.027Cu2.95Ni0.05Ti4-zSnzO12 (z = 0.25–0.4) were synthesized by the solid-state method at 970 °C. The incorporation of doping elements into the ceramic structure after sintering at 1080 °C was confirmed by X-ray diffraction data. Grain morphology and size of various solid solutions were estimated from scanning electron microscopy photographs. The optimal concentrations of doping elements were x = 0.04, y = 0.05, and z = 0.3, which is evident by high permittivity ε′ = 11,000 and low dielectric losses tanδ = 0.051 at f = 1 kHz. La3+, Ni2+ and Sn4+ co-doped CCTO ceramics demonstrated high stability of the permittivity in the temperature range from −60 to +125 °C. Based on the demonstrated dielectric properties, the presented solid solutions are suitable for use in ceramic capacitors.

Sr and Zr Co-Doped CaCu3Ti4O12 Ceramics with Improved Dielectric Properties

The dielectric constant of CCTO materials can be as high as 104, which makes it suitable for use in electronic devices but the high dielectric loss limits its application. In this paper, a series of Sr and Zr co-doped CCTO ceramics having the formula Ca0.8Sr0.2Cu3Ti4−xZrxO12 (x = 0.1, 0.2, 0.3, 0.4) were obtained via a solid-state reaction technique. We force the effect of the Zr content on the phase composition, microstructure, cationic valence states, impedance, and dielectric properties of the as-prepared ceramics to reduce dielectric loss. The results demonstrate that Sr and Zr co-doping increases dielectric constant and reduces dielectric loss simultaneously, and the maximum dielectric constant (1.87 × 105, 1 Hz) and minimum dielectric loss (0.43, 102 Hz) are obtained when x = 0.3. Mixed Cu+/Cu2+ and Ti3+/Ti4+ valence states are observed to coexist in the co-doped material lattices, which promote dipole polarization, and thereby increase the dielectric constant of the ceramics. The dielectric properties of the materials are analyzed according to the internal barrier layer capacitance model, which elucidates the contributions of the grains and grain boundaries to dielectric performance. The maximum grain boundary resistance (3.7 × 105 Ω) is obtained for x = 0.3, which contributes toward the minimum dielectric loss (0.43) obtained for this ceramic at a frequency less than 1 kHz. The average grain sizes of the samples decrease with increasing Zr content, which is the primary factor increasing the grain boundary resistance of the co-doped ceramics.

Investigation of microstructural evolution and suitable potential barrier model for non-linear electrical response of Sr and Nb co-doped CaCu3Ti4O12 ceramics

This work reported about impact of co-doping on structural and non-linear electrical property of CaCu 3 Ti 4 O 12 (CCTO) ceramics with composition Ca 0·95 Sr 0·05 Cu 3 Ti 3·94 Nb 0·06 O 12 prepared by solid state reaction technique. Rietveld refinement of X-ray diffraction data was performed to analyse various parameters for its structure exploration. Microstructure and compositional information of prepared ceramic was determined by SEM, EDX and elemental mapping. The grain size was found 2.32 μm with the use of ImageJ software on SEM images. The identical Raman mode were observed in present doped CCTO ceramics comparative to that reported for pure CCTO in Raman spectroscopy. The resistivity of prepared sample reveals NTC behaviour of the ceramic. The parameters; non-linear coefficient (α = 1.86), breakdown electric field (E b = 191.56V/cm) and leakage current (I = 0.44 mA) were obtained by current voltage measurement at room temperature (RT∼303K). The detail comparative study of various barrier models was carried out and found Schottky barriers as most suited model for potential barrier at grain boundaries in the present system. • Ca0·95Sr0·05Cu3Ti3·94Nb0·06O12 ceramic was synthesized using Solid State Reaction method. • Structural Properties were investigated by XRD, SEM, Raman and FT-IR spectroscopy. • Schottky emission model was found most suitable for non-linear electrical response of prepared ceramics. • The value of nonlinear coefficient and Breakdown field suggest it was suitable for low voltage application. • The present sample exhibits good NTC behaviour at low DC voltage and found useful for varistor and thermistor application.

Giant dielectric behavior and non-ohmic properties in Mg2++F− co-doped CaCu3Ti4O12 ceramics

ABSTRACT A solid–state reaction method was used to produce CaCu3-x Mg x Ti4O12-2x F2x with x values of 0, 0.05, and 0.10. A CaCu3Ti4O12 phase was detected in the absence of impurities. The (Mg2++F–) co–doping ions inhibited the grain growth of the CaCu3Ti4O12 ceramics because of the solute drag mechanism. The dielectric and non–Ohmic electrical properties of the CaCu3-x Mg x Ti4O12-2x F2x ceramics were studied. Intriguingly, the ceramic with x = 0.05 enhanced the dielectric properties with a considerably decreased loss tangent (tanδ~0.06) while retaining a high dielectric permittivity (>104) at 1 kHz. The nonlinear current density–electric field (J–E) properties of the ceramic with x = 0.05 were also successfully improved. However, the dielectric and nonlinear properties deteriorated when x = 0.10. The variations in the low–frequency tanδ and electric breakdown strength were primarily associated with the grain size and Schottky barrier height at the grain boundaries. The relevant mechanisms for these improved dielectric and non–Ohmic properties are discussed based on the effect of the internal barrier layer capacitor.

Origins of a liquid-phase sintering mechanism and giant dielectric properties of Ni+Ge co-doped CaCu3Ti4O12 ceramics

Using a solid-state reaction approach, the structural and electrical parameters of CaCu2.90Ni0.10Ti4-xGexO12 (x = 0.05 and 0.10) ceramics were successfully studied. A single-phase of CaCu3Ti4O12, JCPDS No. 75–2188, was observed in all-ceramic samples. The microstructural changes of these CaCu2.90Ni0.10Ti4-xGexO12 ceramics were directly associated with a liquid-phase sintering mechanism. Investigation of the origin of the liquid-phase sintering mechanism, done using density functional theory, showed that the presence of Ge4+ ions at Cu2+ sites results in a significant decomposition of the related Cu phases. Interestingly, compared to this material with x = 0 (our previous work), the dielectric permittivity of CaCu2.90Ni0.10Ti3.95Ge0.05O12 and CaCu2.90Ni0.10Ti3.90Ge0.10O12 ceramics was meaningfully increased by 24.42% and 43.32%, respectively. Additionally, the loss tangents of these two ceramics were still very low (~0.030–0.035). The low loss tangents observed in CaCu2.90Ni0.10Ti4-xGexO12 ceramics might have originated from oxygen-enrichment at grain boundaries and a metastable insulating layer at grain boundary layers. The result of DC bias trials shows that the dielectric response of CaCu2.90Ni0.10Ti4-xGexO12 ceramics arises mainly from an internal barrier layer capacitor effect.

Microstructure and Improved Dielectric Properties of CaCu <sub>3</sub>Ti <sub>4</sub>O <sub>12</sub> Ceramics by Lanthanum/Europium Co-Doping

In this work, (La, Eu) co-doped CaCu3Ti4O12 ceramics (Ca1-xLaxCu3Ti4-xEuxO12, x = 0.1, 0.3, and 0.5) were prepared by the traditional solid-state method. The XRD results of ceramics confirmed the formation of the single-phase CCTO and a residual amount of CaTiO3. The refined calculation found that the lattice constant of CLCTEO ceramics will be significantly increased due to the co-doping of La and Eu. The FESEM analysis showed a smaller grain size for the co-doped CCTO. Impedance measurements indicated that the (La, Eu) co-doped CCTO ceramics have higher dielectric permittivity than the single-doped with La and Eu. The most negligible dielectric loss was achieved in CLCTEO ceramics with x = 0.1, and a low tanδ of 0.013 was observed at 800kHz for room temperature. The results indicated that the co-doping method is an effective method to improve the dielectric properties.

Strongly Enhanced Dielectric Response and Structural Investigation of (Sr2+, Ge4+) Co-Doped CCTO Ceramics

A solid–state reaction method was used to prepare (Sr2+, Ge4+) co-doped CaCu3Ti4O12 ceramics. A single-phase of CaCu3Ti4O12 was detected in all the ceramics. An enormous evolution of grain growth i...

Colossal dielectric response and relaxation behavior in novel system of Zr4+ and Nb5+ co-substituted CaCu3Ti4O12 ceramics

In this work, we developed a novel system of isovalent Zr4+ and donor Nb5+ co-doped CaCu3Ti4O12 (CCTO) ceramics to enhance dielectric response. The influences of Zr4+ and Nb5+ co-substituting on the colossal dielectric response and relaxation behavior of the CCTO ceramics fabricated by a conventional solid-phase synthesis method were investigated methodically. Co-doping of Zr4+ and Nb5+ ions leads to a significant reduction in grain size for the CCTO ceramics sintered at 1060 °C for 10 h. XRD and Raman results of the CaCu3Ti3.8-xZrxNb0.2O12 (CCTZNO) ceramics show a cubic perovskite structure with space group Im-3. The first principle calculation result exhibits a better thermodynamic stability of the CCTO structure co-doped with Zr4+ and Nb5+ ions than that of single-doped with Zr4+ or Nb5+ ion. Interestingly, the CCTZNO ceramics exhibit greatly improved dielectric constant (~105) at a frequency range of 102–105 Hz and at a temperature range of 20–210 °C, indicating a giant dielectric response within broader frequency and temperature ranges. The dielectric properties of CCTZNO ceramics were analyzed from the viewpoints of defect-dipole effect and internal barrier layer capacitance (IBLC) model. Accordingly, the immensely enhanced dielectric response is primarily ascribed to the complex defect dipoles associated with oxygen vacancies by co-doping Zr4+ and Nb5+ ions into CCTO structure. In addition, the obvious dielectric relaxation behavior has been found in CCTZNO ceramics, and the relaxation process in middle frequency regions is attributed to the grain boundary response confirmed by complex impedance spectroscopy and electric modulus.

Distinct roles between complex defect clusters and insulating grain boundary on dielectric loss behaviors of (In3+/Ta5+) co-doped CaCu3Ti4O12 ceramics

The effects of (In3+/Ta5+) co-dopants on the crystalline structure, microstructure, dielectric response, and electrical properties of CaCu3Ti4-x(Ta0.5In0.5)xO12 ceramics are investigated. By increasing co-doping concentration, the lattice parameter is enlarged, while the mean grain size (98.6 → 11.3 μm) and the dielectric permittivity (ε′≈1.0 × 105 → 3.5 × 104) are significantly reduced, while the low-frequency loss tangent greatly increases. The grain boundary (GB) resistance (Rgb) and capacitance (Cgb) are significantly reduced, corresponding to the variations in tanδ and ε′, respectively. The decrease in Rgb is attributed to a decrease in the conduction activation energy of the GBs from 0.705 to 0.537 eV, while the electrical properties of the grains slightly change. Surprisingly, tanδ values in a low-temperature range (e.g., tanδ ~ 0.03 at −60 °C and 40 Hz) of the CaCu3Ti4-x(Ta0.5In0.5)xO12 ceramics are much lower than that of the CaCu3Ti4O12 ceramic (tanδ ~ 0.10) even though the low-temperature Rgb values of the co-doped ceramics are greatly decreased by ~2–4 orders of magnitude. In a low-temperature range, free electrons can be localized in defect clusters, e.g., In23+-VO··-Cu2+/Cu+/Ti3+, resulting in a low tanδ. In a relatively high-temperature range, tanδ is controlled by Rgb.

Significantly improved giant dielectric response in giant dielectric response in CaCu2.95Ni0.05Ti4-xGexO12 (x = 0.05, 0.10) ceramics

The dielectric properties and electrical responses of an undoped CaCu3Ti4O12 ceramic and isovalent codoped CaCu2.95Ni0.05Ti4-xGexO12 (x = 0.05 and 0.10) ceramics were investigated. Significant increases in the grain size can be observed in all the CaCu2.95Ni0.05Ti4-xGexO12 ceramics. The CaCu2.95Ni0.05Ti4-xGexO12 ceramics were shown to exhibit giant dielectric properties, high dielectric permittivities ∼4.83–4.96 × 104, and very low tanδ values ∼0.029–0.030. Additionally, the ceramics all demonstrated nonlinear current density-electric field (J-E) characteristics. The significantly improved dielectric properties of the (Ni2+, Ge4+)-codoped CaCu3Ti4O12 ceramics are closely associated with the enhanced grain boundary response. Clearly, the giant dielectric properties of the CaCu3Ti4O12 and CaCu2.95Ni0.05Ti4-xGexO12 ceramics could be well described by an internal barrier layer capacitor (IBLC) mechanism, which was confirmed by the results of the impedance spectroscopy and applied DC bias analysis. The important roles of the Ni2+ and Ge4+ isovalent dopants are discussed.

Correction to: Dielectric properties and nonlinear I–V electrical behavior of (Li1+, Al3+) co-doped CaCu3Ti4O12 ceramics

Correction to: Dielectric properties and nonlinear I–V electrical behavior of (Li1+, Al3+) co-doped CaCu3Ti4O12 ceramics

Substantially enhanced varistor properties and dielectric response in (Zn2+, Sn4+) co-doped CaCu3Ti4O12 ceramics

CaCu2.95Zn0.05Ti4-xSnxO12 ceramics with x = 0.05−0.30 were successfully prepared by a conventional solid−state reaction method. The lattice parameter of the sintered ceramics increased with increasing Sn4+ doping concentration. Scanning electron microscopy images show a good dispersion of all major and dopant elements. A homogeneous and fine microstructure with a grain size of ~1.8−2.1 μm was clearly observed in the CaCu2.95Zn0.05Ti4-xSnxO12 ceramics. Substantially enhanced varistor properties for CaCu3Ti4O12 were achieved by co−doping with Zn2+ and Sn4+ ions. Excellent varistor properties with a breakdown electric field of ~1.36 × 104 V/cm and nonlinear coefficient of ~38.26 were achieved in Cu2.95Zn0.05Ti3.70Sn0.30O12 ceramics. The grain boundary resistance was closely correlated with the breakdown electric field and conduction activation energy at the grain boundary, which were increased with increasing Sn4+ doping. The dielectric properties with a dielectric permittivity of ~2,100−5,200 and low loss tangent of ~0.028−0.092 were observed in all CaCu2.95Zn0.05Ti4-xSnxO12 ceramics. The modification of the intrinsic electrical properties of the grain boundaries in Zn2+ and Sn4+ co−doped CaCu3Ti4O12 is the primary reason for the substantially enhanced varistor and improved dielectric properties.

Dielectric properties and nonlinear I–V electrical behavior of (Li1+, Al3+) co-doped CaCu3Ti4O12 ceramics

(Li1+, Al3+) co-doped CaCu3Ti4O12 ceramics (CaCu3−2xLixAlxTi4O12, x = 0.05, 0.1, 0.15) were prepared by a sol–gel method and were sintered at 1020–1080 °C for 8 h to improve the geometric microstructure, dielectric and nonlinear I–V electrical properties. Notably, very high dielectric constant of 1 × 105 with good dielectric-frequency as well as dielectric-temperature stability can be achieved in CaCu2.8Li0.1Al0.1Ti4O12 ceramic sintered at 1060 °C. The average grain sizes, resistivity and the non-Ohmic properties are also improved compared to pure CaCu3Ti4O12. These results indicate that (Li1+, Al3+) co-doping at the Cu2+ site can improve the dielectric properties of CaCu3Ti4O12, supporting the internal barrier layer capacitance effect of Schottky barriers at grain boundaries.

Comparative studies of pure, Sr-doped, Ni-doped and co-doped CaCu3Ti4O12 ceramics: Enhancement of dielectric properties

The CaCu3Ti4O12 ceramic, CCTO, remains as the best material due to its high dielectric constant. In this context, Sr-doped CCTO, Ni-doped CCTO and Sr,Ni co-doped CCTO ceramics were prepared by the solid-state reaction method and were sintered at 1100 °C for 24 h in order to enhance the geometric microstructure and dielectric properties. X-ray diffraction data refined via rietveld method for CaCu3Ti4O12 confirms the formation of single phase. SEM micrographs revealed that the substitution of Sr2+ and/or Ni2+ on Ca and Cu sites respectively increase the grain size of CaCu3Ti4O12 ceramics. Raman scattering measurements shows the presence of TiO2 phase at grain boundaries, which is an important parameter to reduce the dielectric loss of samples. It is found that Sr,Ni co-substitution in CCTO leads to the best dielectric measurements at low frequency. The highest grain boundary resistance value is also obtained for co-doped CCTO sample in the order of 1.84 106 Ω. This value is 10 times higher than pure CCTO. Meanwhile, the nonlinear coefficient values were improved, whereas, the breakdown electric field and leakage current decreased for all ceramic samples and co-doped CCTO is considered as the best conductive grain and insulating grain boundary.

Microstructure and enhanced dielectric properties of yttrium and zirconium co-doped CaCu3Ti4O12 ceramics

CaCu3Ti4O12 (CCTO) ceramics doped with Y2O3, ZrO2, and (Y2O3+ZrO2) were prepared by the citrate-nitrate combustion derived powders in order to investigate the effect of dopants on the microstructure and electrical properties. The results showed that giant dielectric response was enhanced by co-doping of Y3+ and Zr4+ ions at the Ti site. Y2O3 and ZrO2 additive can inhibit the grain growth. Compared with other samples, (Y2O3+ZrO2) co-doped ceramics exhibit a dense and homogenous fine-grained microstructure. A much better temperature and frequency stability of dielectric properties were realized in these ceramics. The dielectric loss (tan δ) < 0.05 in the frequency range of 200 Hz–60 kHz at room temperature, and in the temperature range of 15–72 °C at 10 kHz was successfully accomplished in (Y2O3+ZrO2) co-doped CCTO ceramics. Low tan δ ∼0.039 and high dielectric constant (εr ∼10196) were observed at room temperature and 10 kHz for the above ceramic samples, and the characteristic frequency shifts to higher frequency with increasing measuring temperature. The present results indicate that (Y2O3+ZrO2) co-doping may improve the dielectric properties and increase the grain boundary resistance of CCTO.

Enhanced dielectric properties of Zn and Mn co-doped CaCu3Ti4O12 ceramics

Zn-doped and (Zn+Mn) co-doped CaCu3Ti4O12 ceramics were prepared by the citrate–nitrate combustion derived powders in order to investigate the effect of dopants on the microstructure and electrical properties. The results showed that giant dielectric response was enhanced by co-doping of Zn and Mn. Compared with other samples, (Zn+Mn) co-doped ceramics exhibit a fine-grained microstructure. Much stronger nonohmic properties were realized in these ceramics. It is significant that the (Zn+Mn) co-doping effectively reduced the dielectric loss in the medium frequency region and at room temperature. At x = 0.05 and y = 0.03, low dielectric loss ~0.026 and moderate dielectric constant ~6620 were observed at room temperature and 10 kHz. The present results indicate that (Zn+Mn) co-doping may improve the dielectric properties and increase the grain boundary resistance of CaCu3Ti4O12.

Improved dielectric properties of (Y + Mg) co-doped CaCu3Ti4O12 ceramics by controlling geometric and intrinsic properties of grain boundaries

Significantly improved dielectric properties of CaCu3Ti4O12 ceramics were accomplished by co-doping with Y3+ and Mg2+ to simultaneously control the geometric and intrinsic properties of grain boundaries (GB), respectively. Substitution of these dopants strongly suppressed grain growth while enhancing the resistivity of an individual GB, respectively. The resulting small grained microstructure with very high GB density and greatly increased resistivity resulted in a strong increase in the total resistance of GBs. This caused a large decrease in the loss tangent (tanδ~0.013). Furthermore, nonlinear current–voltage properties were also improved.

A novel approach to achieve high dielectric permittivity and low loss tangent in CaCu3Ti4O12 ceramics by co-doping with Sm3+ and Mg2+ ions

A novel strategy to improve the dielectric properties of CaCu3Ti4O12 ceramics was proposed by co-doping with Sm3+ and Mg2+. Sm3+ substituted in Ca2+ sites can effectively suppress the grain growth, achieving a fine grained ceramic microstructure. Mg2+ was selected to be substituted into Cu2+ sites to enhance the grain boundary (GB) resistivity for reducing the loss tangent (tanδ). High dielectric permittivity ϵ′≈1.25×104 and low tanδ≈0.039 at 1kHz were successfully accomplished in a Ca0.925Sm0.05Cu2.70Mg0.30Ti4O12 ceramic. Non-Ohmic properties were also enhanced. A slight increase in Ti3+/Ti4+ ratio in (Sm+Mg) co-doped CaCu3Ti4O12 ceramics was confirmed by the X-ray absorption near edge structure. Changes in tanδ values for all the co-doped ceramics were very consistent with their variations in GB resistance. The dielectric and non-Ohmic properties of co-doped ceramics were significantly improved by tuning both the geometric and intrinsic factors, i.e., increasing the density of GB layer and enhancing the GB resistance, respectively.

Dielectric properties of CaCu3Ti4O12 improved by chromium/lanthanum co-doping

The dielectric properties of Cr+La co-doped CaCu3Ti4O12 ceramics prepared by a solid-state reaction method were evaluated and compared to Cr-doped, La-doped, and parent CaCu3Ti4O12 (CCTO). Their structure and grain size were evaluated by X-ray diffraction and scanning electron microscopy, respectively. No secondary phase was detected based on the XRD analysis. The results show that, the room temperature dielectric loss of the co-doped samples is reduced to 43% compared to CCTO and their dielectric permittivity is higher than the un-doped, Cr-doped, and La-doped samples at frequencies over 325kHz, 30kHz, and 12Hz, respectively. Furthermore, the temperature stability of the co-doped sample is significantly more convenient than that of CCTO, and its dielectric loss is three times lower. The results also indicated that the co-doping method is effective in reducing the dielectric loss, still maintaining the high dielectric permittivity.