Effects of sintering temperature and Bi2O3, Y2O3 and MgO co-doping on the dielectric properties of X8R BaTiO3-based ceramics

Bi₂O₃, Y₂O₃ and MgO co-doped BaTiO₃ (BT)-based X8R ceramics were synthesized successfully for the first time. The effects of the sintering temperature and Bi₂O₃, Y₂O₃ and MgO dopants on the dielectric properties were investigated systematically. Bi₂O₃ doping can increase the Curie temperature (T_c), but reduces the overall dielectric permittivity. On the other hand, Y₂O₃ doping is beneficial to the formation of core-shell microstructure and the increase of T_c, whereas MgO can prevent excessive Y₂O₃ from diffusing into grain core, and thereby further contributes to the generation of the core–shell microstructure. The generation of the typical core-shell microstructure was confirmed and investigated in detail by using transmission electron microscopy (TEM). It is argued that the synergistic effects of Bi₂O₃, Y₂O₃ and MgO co-doping in terms of the formation of the core-shell structure and the increase of T_c, can help improve the temperature stability of the dielectric permittivity effectively. Increasing the sintering temperature leads to an increase in the grain size, which in turn leads to an increase in the overall dielectric permittivity due to the grain size effect.     

Synthesis and characterization of high performance CaZrO3-doped X8R BaTiO3-based dielectric ceramics

A novel system of lead-free X8R BaTiO₃-based dielectric materials with high dielectric constants was prepared via conventional mixing method. The phase structure, dielectric and electrical properties and the “relaxorlike” characteristic of ceramic materials were systemically studied. The XRD results indicate that no secondary phase formed in the CaZrO₃-doped samples after sintering. SEM micrographs reveal that the grain size of CaZrO₃-doped BaTiO₃-based samples are not uniform, ranging from 0.2 to 0.9 µm. Bulk densities and dielectric properties were measured as a function of CaZrO₃ concentration. The Curie temperatures of all CaZrO₃ doped samples increase due to the existence of an internal stress between grain cores and shells caused by the diffusion of CaZrO₃. The oxygen vacancies have a profound effect on the dielectric loss and frequency characteristics. The 3.5 wt% CaZrO₃-doped sample sintered at 1250 °C showed the optimal dielectric performance (ε_r=4330, tan δ<1.5%, ΔC/C_20 °C≤±14%) that satisfied EIA-X8R specification.     

Simultaneous enhancement of dielectric properties and temperature stability in BaTiO3-based ceramics enabling X8R multilayer ceramic capacitor

Modified BaTiO₃ ceramics that possess high dielectric permittivity and acceptable temperature stability have been widely utilized as multilayer ceramic capacitors (MLCCs) for high-frequency bypass and power filtering in automotive applications. However, since the increasing demand for high-capacity and small-size, high-permittivity materials that can serve as dielectric layers in MLCCs are urgently required. In this work, we design and fabricate a special BaTiO₃-0.03Mg-0.02Y-0.02CaZrO₃ ceramic with a high dielectric permittivity of 3000 and the dielectric variation below ±13% in the temperature range of -55–150°C, fulfilling the requirements of X8R capacitors. To achieve these results, we employed grain size engineering and cation doping, using BaTiO₃ precursors with a particle size of 240 nm to prepare the BaTiO₃-based ceramics with fine grains, while Mg and Y co-doping was used for improving the temperature stability due to dielectric dispersion. Utilizing these high-permittivity BaTiO₃-based materials, we fabricated MLCCs that satisfy the X8R criterion, possessing a high dielectric constant of 2950 and a high breakdown field (410 kV/cm).     

Effect of Bi2O3 additive on dielectric properties of BaTiO3-based ceramics for improving energy density

In this paper, the effect of Bi₂O₃ additive on dielectric properties of BaTiO₃-based ceramics was investigated for improving energy density. When x?=?0.05, the created defect dipoles in BT–BN system achieved a balance in the system with the minimum value of P_r. Because of the created dipole, the long-range dipolar interaction was interrupted and the weak couplings of the defect dipoles were formed. Energy storage density achieved the maximum values of 0.68?J?cm^?3 with energy efficiency 91.5% in 0.95BaTiO₃–Bi_0.05Nb_0.05O₄. The nonlinearity was suppressed obviously with low P_r, which was good for in lead-free relaxor materials for the energy storage applications.     

Effects of Sn on the microstructure and dielectric properties in BaTiO3-based ceramics

Ba_0.985Bi_0.01TiO₃–BaTi_1?xSn_xO₃ powders were synthesized by a two-step soft chemical method. Ceramics with core–shell structure could be easily obtained by using these uniformly distributed powders. The ceramics not only satisfied the requirement of EIA-X8R specification, but also were near to that of EIA-X9R specification. Microstructural evaluation conducted by X-ray diffraction and scanning electron microscopy confirmed the hierarchical structure of the ceramic grains. The shape of the ε–T curves near the dielectric peak became broad when x increased from 0.001 to 0.02. The permittivity of Ba_0.985Bi_0.01TiO₃–BaTi_0.98Sn_0.02O₃ ceramic was ～23,000, ΔC/C_20 °C was ?15%, 14.4% and ?15% at ?55 °C, 120 °C and 170 °C, respectively, and the dielectric loss was 0.5. The results showed that the content of Sn had a strong impact on the diffusion and the dielectric properties of the ceramics.     

Sintering behavior and dielectric properties of KCa2Nb3O10 ceramics

Dense KCa₂Nb₃O₁₀ (KCN) oxides were synthesized and their dielectric properties were investigated. A homogeneous KCN phase was formed in the specimen sintered above 1300 °C, but a CaNb₂O₆ secondary phase was developed in the specimen sintered at 1400 °C, as result of the evaporation of K₂O. The KCN oxides sintered at 1375 °C showed a high relative density that was 97.1% of the theoretical density. Furthermore, liquid-phase-assisted abnormal grain growth occurred during sintering. The dielectric constant of this KCN oxide was 46, with a low dielectric loss of 0.9% at 100 kHz; these values are smaller than those that were previously reported. Complex impedance analysis indicated that the resistivity of the KCN oxide was very low, probably as a result of the presence of K⁺ ions between the layers, and this could be the origin of the low-frequency dispersion of the KCN oxides.     

Microstructure and dielectric characteristics of Nb2O5 doped BaTiO3-Bi(Znl/2Til/2)O3 ceramics for capacitor applications

The effects of Nb₂O₅ addition on the dielectric properties and phase formation of 0.8BaTiO₃-0.2Bi(Zn_l/2Ti_l/2)O₃ (0.8BT-0.2BZT) ceramics were investigated. The desired perovskite phase was achieved with Nb₂O₅ doping levels being in the range of 0.5 wt.%–3.0 wt.%. The 0.8BT-0.2BZT ceramics doped with 1.5 wt.% Nb₂O₅ was found to possess a moderate dielectric constant (ε = 1170) and low dielectric loss (tanδ = 1%) at room temperature and 1 kHz frequency, showing a flat dielectric behavior over the temperature range of −55 °C–200 °C. Based on this composition, the X9R-MLCC (multilayer ceramic capacitor) with Ag0.7-Pd0.3 electrode was sintered at 1060 °C. The optimized capacitance of the MLCC is 26.5 nF, with dielectric loss tanδ of 0.9% and electrical resistance of 4.50 × 10¹¹ Ω at room temperature, leading to a high time constant of 11,900 s, decreasing to 175 s at 200 °C, being one order higher than those of commercial X7R MLCC. In addition, the equivalent series resistance (ESR) was found to be on the order of 0.2 mΩ at 2 MHz, much lower than that of the DC Bus Capacitor Bank for the automotive inverters (where the desired characteristic is <3 mΩ). All these characteristics of the newly developed MLCC will benefit the high temperature and high power capacitor applications.     

Nano-BaTiO3 phase transition behavior in coated BaTiO3-based dielectric ceramics

In this work, the phase structure of BaTiO₃ nanopowders produced by the alkoxide-hydroxide and the hydrothermal method, respectively, was systemically investigated. BaTiO₃ nanopowders with cubic phase produced by the alkoxide-hydroxide method could transform to tetragonal phase when heated to about 1100 °C. Cubic to tetragonal phase transformation behavior of BaTiO₃ nanopowders coated with 0.3BZT-0.7BT or 0.03Nb₂O₅-0.01Co₂O₃ was studied. The internal stress within core-shell structure was proposed to explain the BaTiO₃ phase transformation behaviors. The mismatch of thermal expansion coefficient between core and shell plays a crucial role in cubic to tetragonal phase transformation of BaTiO₃. By tuning the composition of shell and the ratio of the shell to the core, the cubic BaTiO₃ core can transform to tetragonal phase successfully after sintering at 1100 °C in BaTiO₃ based ceramics with core-shell structure and it is mainly resulted by the reduced internal stress between the shell and core.     

Doping behaviors of dysprosium,yttrium and holmium in BaTiO3 ceramics

The difference in doping behaviors of intermediate rare-earth ions and their effects on the dielectric property and microstructure of BaTiO₃(BT)–MgO–Re₂O₃ (Re = Dy, Ho, Y) system were investigated. Compared to Y and Ho, Dy ions provided BT ceramics with a high rate of densification and much enhanced shell formation due to their high solubility in BT. However, the microstructure of the Dy doped specimen was unstable at high temperatures in terms of grain growth. Until the specimen was densified, the tetragonality of Dy doped specimen was remarkably decreased and the substitution amount of Dy ions for A-site was larger than that of Y and Ho ions. After complete densification, the tetragonality was increased again and the B-site incorporation of Dy ions was increased far more than that of Y and Ho ions resulting in grain growth. This different behavior was considered to result in temperature coefficient of capacitance curves in the Dy doped specimen different from that of typical core–shell grains.     

介电温度稳定型BaTiO3基陶瓷材料的研究进展

综述了介电常数温度稳定型BaTiO3基陶瓷的研究进展,从BaTiO3的介电常数和化学掺杂出发,重点介绍了目前国内外BaTiO3的制备及其掺杂方法,展望了介电常数温度稳定型BaTiO3基陶瓷的发展趋势.     

Structural ordering and dielectric properties of Ba3CaNb2O9-based microwave ceramics

Ba₃CaNb₂O₉ is a 1:2 ordered perovskite which presents a trigonal cell within the D_3d³ space group. Dense ceramics of Ba₃CaNb₂O₉ were prepared by the solid-state reaction route, and their microwave dielectric features were evaluated as a function of the sintering time. From Raman spectroscopy, by using group-theory calculations, we were able to recognize the coexistence of the 1:1 and 1:2 ordering types in all samples, in which increasing the sintering time tends to reduce the 1:1 domain, leading to an enhancement of the unloaded quality factor. We concluded that this domain acts as a lattice vibration damping, consequently raising the dielectric loss at microwave frequencies. The best microwave dielectric parameters were determined in ceramics sintered at 1500 °C for 32h: ε′ ~ 43; Q_u×f_r = 15,752 GHz; τ_f ~ 278 ppm °C⁻¹.     

Structure Property Relationship in BaTiO3–Na0.5Bi0.5TiO3–Nb2O5–NiO X8R System

A novel BaTiO₃–Na_0.5Bi_0.5TiO₃–Nb₂O₅–NiO (BT‐NBT‐Nb‐Ni) system that meets the X8R specification (?55°C–150°C, ΔC/C≤±15%) of multilayer ceramic capacitors (MLCCs) was fabricated, with a maximum dielectric constant of 2350 at room temperature (25°C). Core–shell microstructure was observed by transmission electron microscopy (TEM), accounting for the good dielectric temperature stability. The role of Ni on the formation of core–shell structure and phase structure, and the subsequent relationship between structure and dielectric/ionic conduction properties were investigated. It was observed that the addition of Ni could adjust the ratio of core/shell, and significantly reduces the dielectric loss over the studied temperature range. A new Ba₁₁(Ni, Ti)₂₈O_66+x phase with a 10‐layer close‐packed structure was identified by X‐ray diffraction (XRD), serving as a source of oxygen vacancies for ionic conduction in addition to Ba(Ni,Ti)O₃. Furthermore, the impedance spectroscopy measurements demonstrated the remarkable impact of these Ni‐induced oxygen vacancies on both the grain and grain‐boundary conductivities.     

Thickness dependence of dielectric and piezoelectric properties from the surface layer effect of BaTiO3-based ceramics

Nanoscale ferroelectric materials often exhibit a scaling effect of dielectric and piezoelectric properties with thickness. In this work, we demonstrate that a similar scaling effect can also be observed in BaTiO₃ and Ba_0.83Sr_0.17TiO₃ ceramics with a sub-millimeter thickness, as manifested by a reduction of weak-field dielectric constant near the Curie temperature, an increase of the coercive field, and a reduction of piezoelectric response with a reduction of sample thickness, especially for the ceramic with a thickness below 0.5 mm. We propose that the scaling effect could be explained by the presence of surface layers with a stabilized ferroelectric phase and a higher coercive field on ferroelectric ceramics. Because the thickness of the surface layers is typically ~10 μm, our results indicate the surface effect may not be negligible when the dimensions of the ferroelectric materials are in millimeter or sub-millimeter scale. This study is important for the understanding of the scaling effect observed in ferroelectric ceramics.     

Microwave dielectric properties of Co2P2O7 ceramics

Co₂P₂O₇ ceramics were prepared through the traditional solid-state sintering technique. The phase composition, grain size distribution, and densification were researched via X-ray diffraction and scanning electron microscope. The influence of pores on permittivity was described by various models. The dielectric loss was found highly dependent on porosity. Moreover, the low ε_r (<10) values of Co₂P₂O₇ ceramics were explained by the covalent feature of P–O bonds. Raman spectroscopy was used for exploring the relationship between polar phonon modes and dielectric properties in terms of intrinsic factors. The optimum dielectric properties (ε_r = 6.76, Qf = 36,400 GHz and τ_f = ?23.9 ppm/°C) were obtained at 1160 °C for 4 h.     

Simultaneous enhancement of electrical and mechanical properties in CaBi2Nb2O9-based ceramics

CaBi₂Nb₂O₉ (CBN) with Aurivillius phase has an enormous potential in high-temperature piezoelectric devices due to their high Curie temperature and excellent free-fatigue characteristics. Nevertheless, simultaneous enhancement of electrical and mechanical properties in CBN-based ceramics are still a great challenge because of the trade-off between the electrical and mechanical properties. Herein, a strategy, the synergy effect of lattice distortion and oxygen vacancy, is designed to realize the enhanced electrical and mechanical properties of CBN-based ceramics via the domain structure and grain size engineering. The materials can simultaneously deliver a high piezoelectric property of 17.3 pC/N, large hardness of 4.68 GPa, and intensive bending strength of 113.07 MPa, which are enhanced by 346%, 197%, and 141% over those of unmodified CBN ceramics. We believe that the founding of this research opened up a novel and efficient guideline for exploring new bismuth-layered structure ceramics with excellent electrical and mechanical properties.     

Optimized crystal structure and microwave dielectric properties of BaZnSi3O8-based ceramics

In this study, we synthesized BaZnSi₃O₈-based compounds with monoclinic structures (P21/a) using a solid-state method. The crystal structure, phase composition, and microwave dielectric properties of BaZnSi₃O₈-based ceramics were systematically investigated systematically. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images proved that the maximum solubility of BaZn_1-xMg_xSi₃O₈ ranged between 0.3 and 0.4. Rietveld refinement and Phillips–Van Vechten–Levine complex chemical bond theory were used to illustrate the relationship between the microwave dielectric performance and lattice parameters. To further improve the properties, we substituted Ba²⁺ with Sr²⁺ in BaZn_0.8Mg_0.2Si₃O₈. Ba_1-ySr_yZn_0.8Mg_0.2Si₃O₈ remained in a single-phase as y increased from 0 to 1.0. We achieved thermal stability of the resonance frequency of the BaZnSi₃O₈-based ceramics by adjusting TiO₂ to form composite ceramics. After sintering at 1020°C for 5 h, excellent microwave dielectric properties with ε_r = 7.44, Q×f = 57,400 GHz, and τ_f = − 0.2 ppm/°C were realized in the SrZn_0.8Mg_0.2Si₃O₈+8 wt %TiO₂ system.     

Influence of Nb2O5 addition on dielectric properties and diffuse phase transition behavior of BaZr0.2Ti0.8O3 ceramics

Nb₂O₅ doped Ba(Zr_0.2Ti_0.8)O₃ (short as BZT20) ceramics were prepared by a mixed-oxide method using a high-energy planetary ball mill and the influence of Nb₂O₅ addition on microstructure, dielectric properties and diffuse phase transition behavior of BZT20 ceramics were investigated. It was demonstrated that Nb⁵⁺entered the B-site of BZT20 ceramic and substituted for Ti⁴⁺, which caused the expansion and distortion of crystal lattice. BZT20 ceramics doped with 0.2 mol% Nb₂O₅ showed excellent dielectric property and lower diffusivity with ε_m=37,823 and γ=1.49. We supposed that the increase of dielectric constant and decrease of diffuseness parameter with increasing Nb₂O₅ content were caused by lattice disorder and unbalancing of cations induced by the substitution of Ti⁴⁺ by Nb⁵⁺ in the B sites of BZT20 ceramics. The Curie temperature decreased with the increase of Nb₂O₅ content, which can be attributed to enlarged distortion energy of the Nb doped BZT20 structure. Besides, grain size effect on the dielectric property and diffuse phase transition behavior of Nb₂O₅ doped BZT20 ceramics was also investigated.     

Influence of Sr ions on the structure and dielectric properties of Cu/Nb Co-doped BaTiO3 ceramics

Sr-modified Cu/Nb co-doped BaTiO₃ ceramics were prepared using solid-state reactions and the structures and dielectric properties were studied. All the samples had single-phase perovskite structures with no detectable secondary phases. In the low-temperature range, the dielectric constant decreased as the Sr content increased in the high- and low-frequency ranges. Two dielectric constant plateaus accompanied by dielectric relaxation peaks were present in the loss curves, and the relaxation process deviated from the Arrhenius law at low temperatures. The dielectric constants of different plateaus were related to inhomogeneous structures such as grain interiors and grain boundaries. The polarization strength of the grain boundaries in the low-frequency range increased with the temperature and that of the grain interiors demonstrated paraelectric behaviour in high-temperature ranges. An analysis of the electric modulus spectra indicated a close relationship between the relaxation process and resistivity of the grains for high-frequency relaxation. The impedance spectra at high temperatures consist of three electrical responses, corresponding to the effects of grains, grain boundaries, and electrodes. The dielectric relaxation appeared in high temperature range was related to the electrical properties of the grain boundaries.     

Defect structure evolution and electrical properties of BaTiO3-based ferroelectric ceramics

Relaxor perovskite ferroelectric 0.1Bi(Zn_1/2Zr_1/2)O₃-0.9BaTiO₃(0.1BZZ-0.9BT) ceramics were successfully prepared, whose powders synthesized by the sol-gel process, with average grain size about 1.29 μm. 1.75 J/cm³ discharge energy density and good dielectric stability were obtained over a wide temperature range from 25°C to 140°C. The pulse discharge capability of 0.1BZZ-0.9BT ceramics was tested under different electric fields. The discharge time was 2.13 μs, which proved its ability to charge and discharge quickly. Complex impedance analysis and thermally stimulated depolarization current tests were applied to investigate the defect types and activation of 0.1BZZ-0.9BT ceramics. The evolution process of composite defects and oxygen vacancies profoundly affects the dielectric temperature stability of 0.1BZZ-0.9BT ceramics’ energy storage property.     

Ferroelectric domains and luminescent properties of Pr3+-doped Ca2Nb2O7 ceramics

Inorganic luminescent materials based on photoluminescence (PL) and thermoluminescence (TL) display considerable potential applications for optical anti-counterfeiting devices. Ca_2−xNb₂O₇:xPr³⁺ (x = 0.00075, 0.001, 0.002, 0.003, 0.004) ferroelectric ceramics have been fabricated. The basic crystal structure, local ferroelectricity and PL/TL properties of the ceramics have been investigated in this study. The PFM measurement proves that the grains in the prepared ceramics are monodomain state. Furthermore, the synthesized phosphors are embedded into polydimethylsiloxane (PDMS) matrix to fabricate a novel optothermal responsive device with high elasticity, transmittance and heat resistance. The PL and TL photographs of the designed device further demonstrate that the device is promising in practical applications such as optical anti-counterfeiting and information storage.