Magnetic and electric properties,ESR, XPS and NEXAFS spectroscopy of CaCu3Ti4O12 ceramics

ESR, XPS and NEXAFS spectra, as well as magnetic and electric properties of CaCu₃Ti₄O₁₂ synthesized by the solid-phase method within 6,12,24,48 and 60 h were studied. The analysis of magnetic susceptibility of CaCu₃Ti₄O₁₂ and magnesium-containing solid solutions of CaCu_3-3xMg_3xTi₄O₁₂ revealed antiferromagnetic exchange interactions between Cu paramagnetic atoms, while the effective magnetic moment of copper atoms corresponds to the electronic state of Cu(II). In CaCu₃Ti_4-4хMg_4хO_12-δ samples within the whole concentration range the impurity phase MgTiO₃ was observed. The magnetic properties of calcium copper titanate were found to be inconsistent depending on the synthesis duration. The extreme point of magnetic susceptibility was found among samples synthesized within 48 h. Modelling and interpretation of the XPS spectra of CaCu₃Ti₄O₁₂ were performed. Based on the NEXAFS and XPS spectroscopy data, copper and calcium atoms in ceramics display oxidation state +2, while titanium atoms – Ti(IV). ESR spectra of CaCu₃Ti₄O₁₂ samples show an exchange-narrowing signal from copper (II) atoms at g = 2.15. In the ESR spectra of CaCu_3-3xMg_3xTi₄O₁₂ the only intense exchange-narrowed line of Lorentzian form of Cu²⁺ ions is observed. The impedance spectroscopy study of electric properties of CaCu₃Ti₄O₁₂ found the media to feature temperature-dependent reach-through conductivity with activation energy of 0.79–0.71 eV. At 255–300°С, the dominant polarization process is in line with the Gerischer model. It indicates the formation of anionic-cationic associates accompanied by decreased low-frequency capacitance of the samples. With temperatures of over 300°С the samples start displaying ion-migrating polarization which contributes to higher capacitance and dielectric loss at low frequencies. As the temperature grows further to 400°С, the ion migration process gets to dominate within the whole frequency range under study. Based on the study, a conclusion was made on movable cations of copper participating in the polarization process at room temperature.     

Thermal stability improvement of dielectric properties and non-ohmic characteristic of CaCu3+xTi4O12 ceramics via a Cu-nonstoichiometric approach

In this work, the effects of Cu composition on the thermal stability of the dielectric and nonlinear properties of CaCu_3+xTi₄O₁₂ (?0.2 ≤ x ≤ 0.2) ceramics obtained via a polymer-pyrolysis chemical process were studied. The mean grain sizes of Cu-stoichiometric (x = 0), Cu-deficient (x < 0) and Cu-excess (x > 0) CaCu_3+xTi₄O₁₂ ceramics were found to be ~3.2, ~3.4 and ~3.7 μm, respectively. Interestingly, very good dielectric properties (0.020 ≤ tanδ ≤ 0.038 and 4000 ≤ ε′ ≤ 7065) were attained in CaCu_3+xTi₄O₁₂ (?0.2 ≤ x ≤ 0.1, excluding x = 0.2) ceramics. Moreover, the variation of dielectric constant (ε′) within a limit of ±15% (Δε′_{± 15%}) over a wide temperature range (T_R) of ?70 – 220 °C with low tanδ < 0.05 (tanδ_<0.05) over a T_R of ?70 to 80 °C were achieved in a CaCu_2.8Ti₄O₁₂ ceramic. These results suggest that this ceramic could be applicable for X9R capacitors and energy storage devices that require high thermal stability. Additionally, the nonlinear properties of Cu-nonstoichiometric ceramics could be improved when compared with those of the Cu-stoichiometric material. The incremental changes of dielectric and nonlinear properties of CaCu_3+xTi₄O₁₂ (?0.2 ≤ x ≤ 0.2) ceramics revealed the significant role of Cu composition on grain boundary resistance (R_gb), which was confirmed by impedance spectroscopy analysis. In addition, XANES results revealed the proper ratios of Cu⁺:Cu²⁺ and Ti³⁺:Ti⁴⁺ found in these ceramics, indicating the semiconducting behavior of these grains.     

Dielectric properties of conventional and microwave sintered Lanthanum doped CaCu3Ti4O12 ceramics for high-frequency applications

The colossal dielectric response of La-doped CaCu₃Ti₄O₁₂ ceramics has been probed at room temperature for a frequency of 1Hz–20 MHz. In this work, the La-doped (CaCu₃Ti₄O₁₂)_x samples for x = 0.1, 0.2, and 0.3 have been sintered at 1100 °C using two different heating modes. SEM and EDS analysis investigated the microstructural chrysalis, grain size distribution, and the inhibitions of Cu-rich phase segregation into grain boundaries by the effect of La³⁺. The presence of main cubic single-phase of CCTO and the diminutive Bragg peak shift due to ion size effect of La³⁺ and Ca²⁺ have been identified by XRD for both conventional (CS) and microwave sintered (MWS) samples. XPS study revealed the effect of La³⁺ on the binding energies of Cu and Ti in CCTO. The dielectric properties namely dielectric constant (?), tan δ, and dielectric relaxation peaks were measured using BDS in which CS and MWS La-doped samples demonstrated (?) ～ >10⁴ and ～ >10³ along with low tan δ for x ≥ 0.1 at medium and high frequency (10⁴–10⁷Hz) than pure CCTO.     

(Na,K)NbO3–CaCu3Ti4O12 perovskite composites for supercapacitor based piezoelectric devices

The supercapacitor based piezoelectric material composite (Na,K)NbO₃–CaCu₃Ti₄O₁₂ (NKN–CCTO) is investigated for possible application in piezoelectric devices. (1−x)NKN–xCCTO (0.015≤x≤0.06) with different sintering conditions is researched for supercapacitor based piezoelectric applications. The 0.94NKN–0.06CCTO composite sintered at 975 °C shows the highest dielectric permittivity of 796. Clear SEM images of (1−x)NKN–xCCTO reveal that these compositions have high density well-crystallized structures. The composition and sintering temperature dependence of dielectric permittivities and piezoelectric coefficients, plotted in three dimensions, show that the 0.985NKN–0.015CCTO composite sintered at 1025 °C has a moderate dielectric permittivity of 405 and a piezoelectric constant of 98 pC/N.     

X-ray phase,structural, dielectric and magnetic studying of BiFe1-х(M1/2Ti1/2)хO3 (M = Co,Ni, Zn, х = 0–0.11) multiferroics

Perovskite-like rhombohedral distorted solid solutions of BiFe_1-х(M_1/2Ti_1/2)_хO₃ (M = Co, Ni, Zn, x = 0–0.11) were obtained by solid-phase synthesis. An indicator of the solid solution formation is the change of unit cells parameters, that corresponds to the ionic radii of mixed cations (M1/2Ti1/2)3+ (M = Co, Ni, Zn. Solid solutions of BiFe_1-х(M_1/2Ti_1/2)_хO₃ (M = Co, Ni), in contrast to BiFe_1-x(Zn_1/2Ti_1/2)_xO₃ demonstrate ferromagnetic hysteresis pels at room temperature. The x growth in the range from 0.01 to 0.11 for the BiFe_1-х(M_1/2Ti_1/2)_хO₃ system leads to, the saturation magnetization M_S and the remanent magnetization M_R increase from ∼0.1 and ∼2.4⋅10⁻³ emu/g to ∼0.4 and ∼0.038 emu/g respectively. In the same time the coercive force H_c decreases from ∼120 to ∼80 Oe. For the BiFe_1-х(Co_1/2Ti_1/2)_хO₃ system, a noticeably higher magnetic properties with a more complex dependence on x are observed. The maximum parameter values are observed at x = 0.04–0.05: M_S = 0.83 and M_R = 0.24 emu/g, H_c = 1.8 kOe. It is suggested that the detected anomalies of Co-containing solid solutions behavior are related to the one-ionic magnetocrystalline anisotropy of Co²⁺ cations. The BiFe_1-х(M_1/2Ti_1/2)_хO₃ (M = Co, Ni) samples demonstrate piezoelectric constant d₃₃ up to 7 pC/N. Due to the set of properties the materials obtained can be classified as high-temperature multiferroics.     

Improved Dielectric and Nonlinear Electrical Properties of Fine‐Grained CaCu3Ti4O12 Ceramics Prepared by a Glycine‐Nitrate Process

Pure CaCu₃Ti₄O₁₂ was successfully prepared by a glycine‐nitrate process using a relatively low calcination temperature and short reaction time of 760°C for 4 h. Fine‐grained CaCu₃Ti₄O₁₂ ceramics with dense microstructure and small grain size were obtained after sintering for 1 h. The nonlinear coefficient of a fine‐grained CaCu₃Ti₄O₁₂ ceramic calculated in the range 1–10 mA/cm² was found to be very high of ~16.39 with high breakdown electric field strength of 1.46 × 10⁴ V/cm. This fine‐grained CaCu₃Ti₄O₁₂ ceramic also exhibited a very low loss tangent of 0.017 at 20°C with temperature stability over the range ?55°C to 85°C. The grain growth rate of the CaCu₃Ti₄O₁₂ ceramics was found to be very fast after increasing the sintering time from 1.5 to 3 h, leading to formation of a coarse‐grained CaCu₃Ti₄O₁₂ ceramic with grain size of about 100–200 μm. The dielectric permittivity of this coarse‐grained ceramic was found to be as high as 1.03 × 10⁵ with a low loss tangent of 0.054.     

The temperature-dependent piezoelectric and electromechanical properties of cobalt-modified sodium bismuth titanate

Lightly cobalt-modified, Aurivillius-type, sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) ceramics were synthesized by substituting a small amount of cobalt ions onto the Ti⁴⁺ sites using conventional solid-state reaction. X-ray photoelectron spectroscopy (XPS) analysis coupled with bond valence sum calculations show that the dopant cobalt ions substitute for Ti⁴⁺ ions in the form of Co³⁺. The resultant cobalt-modified NBT ceramics (NBT-Co) exhibit better piezoelectric and electromechanical properties by comparison with pure NBT. With only 0.3 wt% Co³⁺ substitution, the piezoelectric properties of the NBT-Co ceramics are optimal, exhibiting a high piezoelectric coefficient (d₃₃~33 pC/N), a low dielectric loss tan δ (~0.1% at 1 kHz), a high thickness planar coupling coefficient (k_t~34%) as well as a high Curie temperature (T_c~663 °C). Such NBT-Co ceramics exhibit nearly temperature-independent piezoelectric and electromechanical properties up to 400 °C, suggesting that these cobalt-modified NBT ceramics are promising materials for high temperature piezoelectric applications.     

The effects of sintered sample thickness on the dielectric properties of CaCu3Ti4O12 ceramics prepared at 1000–1100 °C in air

In this study, the relationship between dielectric properties and sintered sample thickness (d) (0.41–2.74 mm) of CaCu₃Ti₄O₁₂ (CCTO) ceramics prepared at 1000–1100 °C in air was investigated. Compacted green ceramic bodies in varying weights and sintered at different temperatures were prepared to obtain ceramics with varying thicknesses. The samples were evenly polished on either surface, electroded and measured by a precision LCR meter at 20 Hz–1 MHz. The results showed that the ε′ increased monotonically with increasing sintering temperature and indicated a linear relationship with d for samples sintered at ≥1040 °C, while the ε′ for samples sintered at ≤1030 °C was barely affected. Complex impedance analysis showed that the ρ_gb was nearly constant with the change of d. The inverse effect of ε′ and ρ_gb with d can also be observed for the gradual thickness reduction sample sintered at 1040 °C, confirming that the grain boundary plays a key role in the variation of dielectric properties for CCTO ceramics.     

Low-temperature sintering and microwave dielectric properties of Nd(Co1/2Ti1/2)O3 ceramics using glass addition of oxides

The microstructures and microwave dielectric characteristics of complex perovskite Nd(Co_1/2Ti_1/2)O₃ ceramics with 60P₂O₅–15ZnO–5La₂O₃–5Al₂O₃–5Na₂O–5MgO–5Yb₂O₃ (PZLANMY) additions (1–4 wt%) prepared through the conventional solid-state route were investigated. It was found that Nd(Co_1/2Ti_1/2)O₃ ceramics can be sintered at 1210 °C owing to the sintering aid of PZLANMY-glass addition. At 1300 °C, Nd(Co_1/2Ti_1/2)O₃ ceramics with 1 wt% of PZLANMY-glass addition possess a dielectric constant (ε_r) of 27, a Q×f value of 64,000 GHz and a temperature coefficient of resonant frequency (τ_f) of ?29 ppm/°C. The PZLANMY-glass doped Nd(Co_1/2Ti_1/2)O₃ ceramics can find applications in microwave devices that require low sintering temperature.     

Decrease in the dielectric loss of CaCu3Ti4O12 at high frequency by Ru doping

CaCu_3−xRu_xTi₄O₁₂ (x=0, 0.03, 0.05 and 0.07) electronic ceramics were fabricated using a conventional solid-state reaction method. The microstructure, grain sizes and dielectric properties as well as the impedance behaviours of the ceramics were carefully investigated. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) results indicate that ruthenium (Ru) dopant inhibits the growth of grains during the sintering process by promoting the formation of high melting point oxides of Ca and Ti. The study on the frequency dependence of dielectric properties suggests that Ru doping shifts the dielectric loss peak of CCTO to a much lower frequency, thereby reducing the dielectric loss of CCTO at high frequency (f>1.0 MHz) accordingly. When doped with proper amount of Ru, the high frequency dielectric loss of CCTO is reduced to a very low value (tanδ<0.05). Our study conclusively suggests that Ru-doped CCTO, with sufficiently low dielectric loss and decent permittivity, presents potential applications at high frequency.     

A novel strategy to enhance dielectric performance and non-Ohmic properties in Ca2Cu2−xMgxTi4O12

A novel strategy to improve the dielectric and non-Ohmic properties of CaCu₃Ti₄O₁₂ ceramics that deliberately created a binary-phase system of CaCu_3−xMg_xTi₄O₁₂/CaTiO₃ was proposed and can be performed with a starting nominal formula of Ca₂Cu_2−xMg_xTi₄O₁₂. Mg²⁺ doping ions were preferentially incorporated only into the CaCu₃Ti₄O₁₂ phase. Substitution of Mg²⁺ into CaCu₃Ti₄O₁₂/CaTiO₃ can cause a significant increase in dielectric permittivity and a large reduction of the loss tangent to <0.015 at 1 kHz; while, retaining excellent temperature dielectric-stability. Sintering time had a slight influence on the dielectric properties, but remarkable effects upon the nonlinear electrical properties of CaCu_3−xMg_xTi₄O₁₂/CaTiO₃ ceramics. Degradation of nonlinear properties with increased sintering time is suggested to be the result of the dominant effect of oxygen vacancies. Impedance spectroscopy analysis demonstrated that improved dielectric and nonlinear properties could be attributed to the enhanced electrical responses of CaCu₃Ti₄O₁₂–CaTiO₃ and CaCu₃Ti₄O₁₂–CaCu₃Ti₄O₁₂ interfaces resulting from Mg²⁺ doping ions.     

Electrical properties of CaBi4Ti4O15–Bi4Ti3O12 piezoelectric ceramics

CaBi₄Ti₄O₁₅–Bi₄Ti₃O₁₂ (CBT–BIT) ceramics were synthesized using a solid state reaction method. The X-ray diffraction (XRD) analysis revealed the existence of bismuth layered perovskite phase with orthorhombic crystal structure. High-resolution transmission electron microscopy (HRTEM) confirmed the alternate arrangement of CBT part and BIT part along c axis in the intergrowth structure. CBT–BIT ceramics showed excellent thermal stability of the dielectric loss (tan δ), but the relaxation of dielectric loss in the 100 Hz to 1 MHz frequency range had been observed. Meanwhile, an enhanced piezoelectric constant (d₃₃) value of 15 pC/N was observed without degradation even the temperature up to 650 °C. The dc resistivity (ρ_dc) of CBT–BIT performed a high value of 5.68×10¹⁴ (Ω cm) at room temperature (RT). In addition, the ρ_dc values of CBT–BIT within the temperature range of 100–450 °C were close to those of CBT and kept almost one hundred times higher than those of BIT.     

SHS-produced Co<Superscript>2+</Superscript>Ti<Superscript>4+</Superscript>-doped barium and strontium hexaferrites: Static and dynamic magnetic properties

Static and dynamic magnetic properties of SHS-produced BaFe_12–2x (Co _х Ti _х )O₁₉ (х = 1.0, 1.1, 1.2) and SrFe_12–2y (Co _y Ti _y )O₁₉ (0 ≤ y ≤ 1.0) hexaferrites were characterized by magnetization and FMR measurements. Dynamic properties of SrFe_12–2y (Co _y Ti _y )O₁₉ hexaferrites were rationalized in terms of not only magnetic anisotropy but also the anisotropy of magnetomechanical ratio. SHS-produced ferrites can be recommended for designing radar-absorbent coatings and other SHF devices operating in the range 20–50 GHz.     

Impedance spectroscopy and magneto-dielectric analysis of La3+ substituted Co2Z hexaferrite

Single phase Ba₃Co₂Fe₂₄O₄₁ (Co₂Z) and Ba_2.8La_0.2Co₂Fe₂₄O₄₁ (La-Z) were prepared by solid state ceramic method. The dielectric, impedance and electric modulus were systematically investigated as a function of temperature from 50 °C–250 °C and in the frequency range of 1 Hz–1 MHz. Frequency dependent imaginary impedance and electric modulus implies that La³⁺ substitution significantly affect hopping and relaxation mechanism of charge carriers. Cole-Cole plots (Z" vs Z') has been fitted with suitable equivalent circuit for both Co₂Z & La-Z. The obtained grain and grain boundary resistances confirmed that charge carriers experienced lower resistance in La-Z. Arrhenius plots of relaxation time (τ) vs 1/T showed parallel conduction mechanism in system. Complex electric modulus spectrum distinguished the capacitive contribution of grain, grain boundary and electric effect. A very high magnetodielectric effect at low frequencies has been observed for La-Z.     

Enhanced electrical and photoluminescence properties of BiSbO4-doped CaCu3Ti4O12 ceramics by modifying grain boundary response

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.     

A Novel One‐Step Flame Synthesis Method for Tungsten‐Doped CCTO

An efficient synthesis is used for the first time to prepare CaCu₃Ti_4?xW_xO₁₂ (x = 0.01, 0.03, and 0.05) electroceramics for energy storage capacitors. CaCu₃Ti_4?xW_xO₁₂ ceramics are synthesized via flame synthesis of metal nitrates precursors in nonaqueous solution using cheap, stable, and insoluble solid TiO₂ powder. The pathway yielded a CaCu₃Ti₄O₁₂ (CCTO) phase with the traces of CuO and CaTiO₃ sintered at 1050°C for 30 h. The SEM micrograph shows the grains with smooth surfaces associated with cubical appearance and the size range of 1.5–7, 2.0–7.5, and 2.0–8.0 μm for CCTWO01, CCTWO03, and CCTWO05, respectively. The EDX and XPS analyses show the presence of Ca, Cu, Ti, W, and O elements confirming the purity of these ceramics. The complex impedance and modulus (M) spectroscopy show that the dielectric constant (ε_r) values of the W‐doped CCTO were dominantly affected by the electrical properties of the grain boundary, which is also evident from the SEM micrographs. The grain‐boundary resistance decreased with increasing tungsten content. The activation energies for the grain boundaries were calculated from the impedance and modulus data using the slope of the ln τ versus 1/T and were found to be in the range 0.62–0.67 eV.     

Co-doping effects of A-site Y3+ and B-site Al3+ on the microstructures and dielectric properties of CaCu3Ti4O12 ceramics

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.     

Effect of oxygen sintering atmosphere on the electrical behavior of CCTO ceramics

The CaCu₃Ti₄O₁₂ ceramics were sintered in air and pure O₂ atmosphere, respectively, and the effect of pure O₂ atmosphere on the electrical behavior of the CaCu₃Ti₄O₁₂ ceramics was investigated. It was found that the dielectric properties of the CaCu₃Ti₄O₁₂ ceramics displayed a Debye-like relaxation between 20 Hz and 1 MHz, but the permittivity of the sample sintered in pure O₂ atmosphere was decreased drastically. Moreover, the I-V behavior of the ceramic sintered in pure O₂ atmosphere presented a linear feature. With XPS analysis, it was illustrated that the valence of Cu and Ti elements in the CaCu₃Ti₄O₁₂ ceramics had obviously been influenced by the O₂ concentration. Based on the experimental comparison of CaCu₃Ti₄O₁₂ ceramics sintered in air and pure O₂ atmosphere, it was suggested that the valence of metallic elements and defects played key role for the origin of the giant permittivity and I-V nonlinear feature in the CaCu₃Ti₄O₁₂ ceramics.     

Preparation, characterization and dielectric properties of CaCu3Ti4O12 ceramics

CaCu₃Ti₄O₁₂ nano-sized powders were successfully prepared by sol-gel technique and calcination at 600-900 °C. The thermal decomposition process, phase structures and morphology of synthesized powders were characterized by IR, DSC-TG, XRD, TEM, respectively. It was found that the main weight-loss and decomposition of precursors occurred below 450 °C and the complex perovskite phase appeared when the calcination temperature was higher than 700 °C. Using above synthesized powders as starting materials, CCTO-based ceramics with excellent dielectric properties (?₂₅ = 5.9 × 10⁴, tan δ = 0.06 at 1.0 kHz) were prepared by sintering at 1125 °C. According to the results, a conduction mechanism was proposed to explain the origin of giant dielectric constant in CCTO system.     

Ge4+ doped CaCu2.95Zn0.05Ti4O12 ceramics: Two-step reduction of loss tangent

CaCu₃Ti₄O₁₂ ceramics have been extensively studied for their potential applications as capacitors in recent years; however, these materials exhibit very large dielectric losses. A novel approach to reducing the dielectric loss tangent in two steps, while increasing the dielectric permittivity, is presented herein. Doping CaCu₃Ti₄O₁₂ with a Zn dopant reduces the loss tangent of the ceramic material from 0.227 to 0.074, which is due to the increase in grain boundary (GB) resistance by an order of magnitude (from 6.3× 10³ to 3.93 × 10⁴ Ω cm). Zn-doping slightly changes the microstructure and dielectric permittivity of the CaCu₃Ti₄O₁₂ ceramic, which reveals that the primary role of the Zn dopant is to tune the intrinsic properties of the GBs. Surprisingly, the addition of the Ge⁴⁺ dopant into the Zn²⁺-doped CaCu₃Ti₄O₁₂ ceramic sample led to a further decrease in the loss tangent from 0.074 to 0.014, due to enhanced GB resistance (3.1 × 10⁵ Ω cm). The grain size increased remarkably from 2–3 μm to 85–90 μm, corresponding to a significant increase in the dielectric permittivity (~1–4 × 10⁴). The large increase in GB resistance is due to the intrinsic potential barrier height at the GBs and the segregation of the Cu-rich phase in the GB region. First-principles calculations revealed that Zn and Ge are preferentially located at the Cu sites in the CaCu₃Ti₄O₁₂ structure. The substitution of the Ge dopant does not hinder the role of the Zn dopant in terms of improving the electrical properties at the GBs. These phenomena are effectively explained by the internal barrier layer capacitor model. This study provides a way of improving the dielectric properties of ceramics for their practical use as capacitors.