Improved non-ohmic and dielectric properties of Cr3+ doped CaCu3Ti4O12 ceramics prepared by a polymer pyrolysis solution route

CaCu_3-xCr_xTi₄O₁₂ (x?=?0.00–0.20) ceramics were prepared via a polymer pyrolysis solution route. Their dielectric properties were improved by Cr³⁺ doping resulting in an optimal dielectric constant value of 7156 and a low tanδ?value of 0.092 in a sample with x?=?0.08. This might have resulted from a decrease in oxygen vacancies at grain boundaries. XANES spectra confirmed the presence of Cu⁺ ions in all ceramic samples with a decreasing Cu⁺/Cu²⁺ ratio due to an increased content of Cr³⁺ ions. All CaCu_3-xCr_xTi₄O₁₂ ceramics showed nonlinear characteristic with improvement in both the breakdown field (E_b) and its nonlinear coefficient (α). Interestingly, the highest values of α, ～ 114.4, and that of E_b, ～8455.0?±?123.6?V?cm^?1, were obtained in a CaCu_3-xCr_xTi₄O₁₂ sample with x?=?0.08. The improvement of dielectric and nonlinear properties suggests that they originate from a reduction of oxygen vacancies at grain boundaries.     

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

The microstructural evolution, non‐Ohmic properties, and giant dielectric properties of CaCu₃Ti_4?xGe_xO₁₂ 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 CaCu₃Ti_4?xGe_xO₁₂ 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.     

Structural dependence of microwave dielectric properties in ilmenite-type Mg(Ti1-xNbx)O3 solid solutions by Rietveld refinement and Raman spectra

Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics were prepared by the conventional solid-state reaction method. The phase composition, sintering characteristics, microstructure and dielectric properties of Ti⁴⁺ replacement by Nb⁵⁺ in the formed solid solution Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics were systematically studied. The structural variations and influence of Nb⁵⁺ doping in Mg(Ti_1-xNb_x)O₃ were also systematically investigated by X-ray diffraction and Raman spectroscopy, respectively. X-ray diffraction and its Rietveld refinement results confirmed that Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics crystallised into an ilmenite-type with R-3 (148) space group. The replacement of the low valence Ti⁴⁺ by the high valence Nb⁵⁺ can improve the dielectric properties of Mg(Ti_1-xNb_x)O₃ (x = 0–0.09). This paper also studied the different sintering temperatures for Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics. The obtained results proved that 1350 °C is the best sintering temperature. The permittivity and Q × f initially increased and then decreased mainly due to the effects of porosity caused by the sintering temperature and the doping amount of Nb₂O₅, respectively. Furthermore, the increased Q × f is correlated to the increase in Ti–O bond strength as confirmed by Raman spectroscopy, and the electrons generated by the oxygen vacancies will be compensated by Nb⁵⁺ to a certain extent to suppress Ti⁴⁺ to Ti³⁺, which was confirmed by XPS. The increase in τ_f from ?47 ppm/°C to ?40.1 ppm/°C is due to the increment in cell polarisability. Another reason for the increased τ_f is the reduction in the distortion degree of the [TiO₆] octahedral, which was also confirmed by Raman spectroscopy. Mg(Ti_0.95Nb_0.05)O₃ ceramics sintered at 1350 °C for 2 h possessed excellent microwave dielectric properties of ε_r = 18.12, Q × f = 163618 GHz and τ_f = ?40.1 ppm/°C.     

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.     

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.     

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.     

Extremely Enhanced Nonlinear Current–Voltage Properties of Tb‐Doped CaCu3Ti4O12 Ceramics

Nonlinear current–voltage properties of CaCu₃Ti₄O₁₂ ceramics were extremely enhanced by doping with Tb. Substitution of Tb to CaCu₃Ti₄O₁₂ resulted in a decrease in grain size due to the ability of Tb ions to inhibit grain boundary mobility. The dielectric properties of CaCu₃Ti₄O₁₂ ceramics were degraded after doping with Tb. Surprisingly, the nonlinear electrical properties were strongly enhanced. The best properties with a nonlinear coefficient of ~29.67 and breakdown electric field strength of ~1.52 × 10⁴ V/cm were obtained in the Ca_0.775Tb_0.15Cu₃Ti₄O₁₂ ceramic. These extremely enhanced properties were attributed to modification of grain boundary electrical response due to the effect Tb substitution.     

Giant dielectric behavior of monovalent cation/anion (Li+, F−) co-doped CaCu3Ti4O12 ceramics

Giant dielectric behavior and electrical properties of monovalent cation/anion (Li⁺, F⁻) co-doped CaCu₃Ti₄O₁₂ ceramics prepared by a solid-state reaction route were systematically investigated. Substitution of Li⁺ and F⁻ led to a significantly enlarged mean grain size. A reduced loss tangent (tanδ ~0.06) with the retainment of an ultra-high dielectric permittivity (ε′ ~7.7-8.8 × 10⁴) was achieved in the co-doped ceramics, while the breakdown electric field and nonlinear coefficient of CaCu₃Ti₄O₁₂ ceramics were increased by co-doping with (Li⁺, F⁻). The variations in nonlinear electrical properties and giant dielectric response, as well as the dielectric relaxation, were well explained by the Maxwell-Wagner polarization model for an electrically heterogeneous microstructure, in which a Schottky barrier height at the grain boundaries (GBs) was formed. ε′ was closely correlated to the GB capacitance. Significantly decreased tanδ value and enhanced nonlinear properties were related to a significant increase in the GB resistance, which was attributed to the significantly increased potential barrier height and conduction activation energy at the GBs. The semiconducting nature of the grains was also studied using X-ray photoelectron spectroscopy and found to originate from the presence of Cu⁺ and Ti³⁺ ions.     

Enhanced intrinsic permittivity and bulk response in Y2/3Cu3Ti4+xO12 ceramics

Considering the contribution of the mixed valence structure of Ti³⁺ and Ti⁴⁺ to the semiconductivity of grain, compositions with the formula of Y_2/3Cu₃Ti_4+xO₁₂ were designed and prepared. The dielectric bulk responses of Y_2/3Cu₃Ti_4+xO₁₂ ceramics were explored in detail. Changing Ti stoichiometry gives rise to an increase of the intrinsic permittivity. Y_2/3Cu₃Ti_3.925O₁₂ ceramic exhibits a higher intrinsic permittivity of ~120 at 60 MHz than that of pure Y_2/3Cu₃Ti₄O₁₂ ceramics (87 at 60 MHz). Additionally, the activation energies of bulk responses are significantly enhanced by changing Ti stoichiometry, which is closely linked with the increase of Ti³⁺/Ti⁴⁺.     

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.     

Origin of significantly enhanced dielectric response and nonlinear electrical behavior in Ni2+-doped CaCu3Ti4O12: Influence of DC bias on electrical properties of grain boundary and associated giant dielectric properties

CaCu_3-xNi_xTi₄O₁₂ (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 CaCu_3-xNi_xTi₄O₁₂ 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 CaCu_3-xNi_xTi₄O₁₂ 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.     

Microstructural,dielectric, and nonlinear properties of Ca1–xCdxCu3Ti4O12 thin films

The effects of the A-site transition from Ca²⁺ to Cd²⁺ on the microstructure, morphology, and electrical properties of Ca_1–xCd_xCu₃Ti₄O₁₂ thin films were studied. The film surfaces are smooth, compact, and without cracks. The CaCu₃Ti₄O₁₂ and CdCu₃Ti₄O₁₂ films had similar morphologies and electrical properties. The grain size initially increased and subsequently decreased with the transition from Ca²⁺ to Cd²⁺ at the A site. The change in Ca sites has an obvious effect on Cu sites. The film with more copper-rich phases at the grain boundaries had the largest grain size when Ca²⁺ and Cd²⁺ equally occupied the A sites. The dielectric constant of Ca_1–xCd_xCu₃Ti₄O₁₂ was closely related to the copper oxide secondary phase. The dielectric loss tangent and nonlinearity coefficient were associated with the compact structure, copper oxide secondary phase, copper vacancies and improved grain boundary response. The simultaneous occupancy of the A sites by Ca²⁺ and Cd²⁺ improves the dielectric and nonlinear properties of Ca_1–xCd_xCu₃Ti₄O₁₂. Optimal dielectric properties (?_r = 5238 and tan δ = 0.009 at 1 kHz) and an enhanced nonlinearity coefficient (～4.22) were simultaneously obtained for the Ca_0.5Cd_0.5Cu₃Ti₄O₁₂ thin film. This study demonstrates that the extrinsic mechanism is the main origin of the high dielectric constant values in Ca_1–xCd_xCu₃Ti₄O₁₂ films. The resulting films are suitable for applications in capacitors.     

A/B-site cosubstituted Ba4Pr28/3Ti18O54 microwave dielectric ceramics with temperature stable and high Q in a wide range

High permittivity Ba₄(Pr_1-xSm_x)_28/3Ti_18-yAl_4y/3O₅₄(0.4≤x ≤ 0.7, 0≤y ≤ 1.5) ceramics were synthesized using a standard solid-state method. The effects of Sm³⁺ substitution into the A-site and Sm³⁺/Al³⁺ cosubstitution into the A/B-sites on the microstructure, crystal structure, Raman spectra, infrared reflectivity (IR) spectra and dielectric characteristics were investigated in a Ba₄Pr_28/3Ti₁₈O₅₄ solid solution. In the ceramic samples of Ba₄(Pr_1-xSm_x)_28/3Ti₁₈O₅₄(0.4≤x ≤ 0.7), Sm³⁺ partial substitution for Pr³⁺ could improve the quality factor (Qf) value and reduce the TCF value. Nevertheless, the quality factor (Qf~10,000GHz) needed further improvement and the TCF values (+12.3~+35.4 ppm/°C) were still too large. Therefore, Al³⁺ was introduced for further optimization of the TCF values and Qf values of the Ba₄(Pr_1-xSm_x)_28/3Ti₁₈O₅₄ ceramics. Sm/Al cosubstitution led to a good combination of high ε_r (ε_r ≥ 70), high Qf (Qf ≥ 12,000 GHz), and near-zero TCF (−10 < TCF < +10 ppm/°C) in a wide range (0.4≤x ≤ 0.7). Infrared reflectivity (IR) spectra indicated that A-TiO₆ vibration modes gave the primary contribution rather than Ti–O bending and stretching modes. The decrease in the degree of B-site cations order could be confirmed by Raman spectra. XPS results demonstrated that the improvement of quality factor (Qf) value was strongly related to the suppression of Ti³⁺. Excellent dielectric properties were achieved in Ba₄(Pr_1-xSm_x)_28/3Ti_18-yAl_4y/3O₅₄ microwave ceramics with x = 0.5 and y = 1.25: ε_r = 72.5, Qf = 13,900GHz, TCF = +1.3 ppm/°C.     

Bond characteristics and microwave dielectric properties on Zn3-xCux(BO3)2 ceramics with ultralow dielectric loss

The crystal structure and microwave dielectric properties of Zn_3-xCu_x(BO₃)₂ (x = 0–0.12) ceramics prepared via a traditional solid-state reaction method were investigated by means of X-ray diffraction (XRD) utilizing the Rietveld refinement, complex chemical bond theory, and Raman spectroscopy. XRD showed that all samples were single phase. The samples maintained a low permittivity, even at higher Cu²⁺ contents, which is conducive to the shortening of signal delay time, and intimately related to the average bond ionicity and Raman shift. Moreover, proper Cu²⁺ substitution greatly reduced the dielectric loss associated with the lattice energy. Cu²⁺ entering the lattice optimized the temperature coefficient of resonance frequency (τ_f) values and improved the temperature stability of samples by affecting the bond energy. Optimal microwave dielectric properties were: ε_r = 6.64, Q × f = 160,887 GHz, τ_f = ?42.76 ppm/°C for Zn_2.96Cu_0.04(BO₃)₂ ceramics sintered at 850 °C for 3 h, which exhibited good chemical compatibility with silver and are therefore good candidate materials for Low temperature co-fired ceramic applications.     

A Novel Route to Greatly Enhanced Dielectric Permittivity with Reduce Loss Tangent in CaCu3−xZnxTi4O12/CaTiO3 Composites

Dielectric and nonlinear properties of a binary compound derived from Ca₂Cu₂Ti₄O₁₂ were greatly improved by doping with Zn²⁺ to deliberately create CaCu_3–xZn_xTi₄O₁₂/CaTiO₃ composites. Ca₂Cu_1.8Zn_0.2Ti₄O₁₂ composition can exhibit an enhanced ε′, ~6,513, with a strong reduction in tanδ to ~0.015 (at 1 kHz). The nonlinear coefficient and breakdown field strength were significantly enhanced. The dielectric and nonlinear properties were described based on the effect of Zn²⁺ substitution on electrical response of internal interfaces.     

Effect of substituting Al3+ for Ti4+on the microwave dielectric performance of Mg2Ti1-xAl4/3xO4 (0.01 ≤ x ≤ 0.09) ceramics

In this paper, Mg₂Ti_1-xAl_4/3xO₄ ceramics (0.01 ≤ x ≤ 0.09) were synthesized through conventional solid-state ceramic route. The cubic spinel structure, microstructure and microwave properties of Mg₂Ti_1-xAl_4/3xO₄ (x = 0.01, 0.03, 0.05, 0.07, 0.09) ceramics were investigated by X-ray diffraction, Raman spectra, infrared spectra. Rietveld refinements confirm that a spinel structure phase with space group Fd-3m is formed. The variation of the permittivity was concerned with the ionic polarizability, and the value of τ_f was influenced by the bond valence. Both Q × f values and relative density showed an identical trend. Intrinsic properties of Mg₂Ti_1-xAl_4/3xO₄ ceramics were analyzed by infrared spectra and Raman spectra. In addition, the Mg₂Ti_1-xAl_4/3xO₄ ceramic sintered at 1420 °C for 4 h possessed optimal dielectric properties (ε_r = 14.65, Q × f = 182347 GHz, τ_f = −57.7 ppm/°C) when x = 0.09.     

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.     

Influence of inverse spinel structured CuGa2O4 on microwave dielectric properties of normal spinel ZnGa2O4 ceramics

Spinel Zn_1‐xCu_xGa₂O₄ (x = 0‐0.15) ceramics were prepared by the conventional solid‐state method. Only a single phase was indexed in all samples. The continuous lattice contraction of ZnGa₂O₄ unit cell was caused by Cu²⁺ substitution, and the lattice parameter shows a linear correlation with the content of Cu. The refined crystal structure parameters suggest that Cu²⁺ preferentially occupies the octahedron site, and the degree of inversion of Zn_1‐xCu_xGa₂O₄ (x = 0‐0.15) ceramics almost equals to the content of Cu²⁺. The relative intensity of A*_1g mode in Raman spectra confirm that the degree of inversion climbed with the growing content of Cu²⁺. The experimental and theoretical dielectric constant of Zn_1‐xCu_xGa₂O₄ ceramics fit well. Zn_1‐xCu_xGa₂O₄ (x = 0.01) ceramics sintered at 1400°C for 2 h exhibited good microwave dielectric properties, with ε_r = 9.88, Q × f = 131,445 GHz, tanδ = 6.85 × 10^?5, and τ_f = ?60 ppm/°C.     

Effect of strontium substitution on the structure and dielectric properties of unfilled tungsten bronze Ba4-xSrxSmFe0.5Nb9.5O30 ceramics

The effects of Sr²⁺ substitution for Ba²⁺ on phase structure, microstructure, dielectric and electric properties for Ba_4-xSr_xSmFe_0.5Nb_9.5O₃₀ (x = 0, 1, 2, 3 and 4) ceramics were systematically researched. X-ray diffraction patterns show that Ba_4-xSr_xSmFe_0.5Nb_9.5O₃₀ (x = 0, 1, 2 and 3) ceramics are tetragonal tungsten bronze compound with a space group of P4bm, while the sample for x = 4 is an orthorhombic structure compound. The result can be corroborated by the analysis of Raman spectroscopy. As the Sr²⁺ contents increase from 0 to 3, the full width at half maximum of Raman lines of all samples increase gradually, indicating that the degree of lattice distortion increase. All tetragonal tungsten bronze ceramics exhibited a broad permittivity peaks, accompanied by frequency dispersion, indicating all samples are relaxor. The electrical properties of BSSFN ceramics were further studied by complex impedance spectroscopy. XPS spectrum shows that Fe²⁺ and Fe³⁺ coexist in Ba_4-xSr_xSmFe_0.5Nb_9.5O₃₀ ceramics, and their proportion varies with the concentration of Sr²⁺.     

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

Dielectric materials with ultrahigh permittivity are attracting attention due to the increasing demand for these types of materials for microelectronics and energy storage applications. In this work, we successfully synthesized Zn-doped CdCu₃Ti₄O₁₂ (CdCTO) ceramics with low dielectric loss and large permittivity via an ordinary mixed-oxide technique. Remarkably, at a Zn doping level of 0.10, a CdCu_2.9Zn_0.1Ti₄O₁₂ ceramic exhibited both decreased dielectric loss tangent of ~0.058 and large dielectric permittivity > 4.0 × 10⁴, as well as a good frequency stability over a wide frequency range from 40 Hz to 10⁶ Hz. The high dielectric performance was attributed to the enhanced grain boundary resistance and internal barrier layer capacitor (IBLC) effect due to the fine and uniform grains that formed upon Zn doping. The findings reported in this work provide valuable insights into how to simultaneously realize a low dielectric loss and high permittivity in CdCTO and other related dielectric ceramics.