Good dielectric performance and broadband dielectric polarization in Ag,Nb co-doped TiO2

Due to the demand of miniaturization and integration for ceramic capacitors in electronic components market, TiO₂-based ceramics with colossal permittivity has become a research hotspot in recent years. In this work, we report that Ag⁺/Nb⁵⁺ co-doped (Ag_1/4Nb_3/4)_xTi_1−xO₂ (ANTOx) ceramics with colossal permittivity over a wide frequency and temperature range were successfully prepared by a traditional solid–state method. Notably, compositions of ANTO0.005 and ANTO0.01 respectively exhibit both low dielectric loss (0.040 and 0.050 at 1 kHz), high dielectric permittivity (9.2 × 10³ and 1.6 × 10⁴ at 1 kHz), and good thermal stability, which satisfy the requirements for the temperature range of application of X9R and X8R ceramic capacitors, respectively. The origin of the dielectric behavior was attributed to five dielectric relaxation phenomena, i.e., localized carriers' hopping, electron–pinned defect–dipoles, interfacial polarization, and oxygen vacancies ionization and diffusion, as suggested by dielectric temperature spectra and valence state analysis via XPS; wherein, electron-pinned defect–dipoles and internal barrier layer capacitance are believed to be the main causes for the giant dielectric permittivity in ANTOx ceramics.     

Grain size engineered high-performance nanograined BaTiO3-based ceramics: Experimental and numerical prediction

The ultra-thin multilayer ceramic capacitors (MLCCs) with layer thickness less than 1 μm or even 0.5 μm are in urgent demand due to the rapid development of modern electronic industries. Notably, the dielectric and ferroelectric properties of nanograined BaTiO₃-based ceramics, which are widely used as dielectric materials in MLCCs, are highly related to grain size. In this work, nanograined BaTiO₃-based ceramics with various grain sizes (50-100 nm) were prepared via the chemical coating method. The grain size effect on the dielectric and energy storage properties were systematically investigated. TEM and EDS images demonstrate that the typical core-shell structure is obtained inside ceramic grains even if the grain size is reduced to 50 nm. The fine-grain ceramic displays a lower maximal polarization but a higher breakdown strength, which ascribes to its weaker ferroelectric contribution and higher grain boundary ratio, respectively. As a result, it is confirmed that there exists an optimal grain size around 70 nm where maximum discharge energy density is achieved under the synergy effect of breakdown strength and polarization, which is also verified by a finite element analysis based on a modified hyperbolic tangent model. All these features provide important guidance towards the design of ultra-thin layer MLCCs by optimizing the dielectric properties and energy storage performance while pursuing miniaturization.     

Defect control of Yb-doped dielectric ceramics on improving the reliability for MLCC application

A fine-grained Yb-doped (Ba_1-xCa_x)_mTiO₃ (BCT)-based ceramic, possessing high dielectric properties and outstanding reliability under a reducing atmosphere sintering, was synthesized by the chemical coating method. The mean grain size of the ceramics was 170 nm. A distinct core-shell structure of ceramics was observed by the TEM-EDS measurement. With increasing content of Yb, the curie temperature increased and the DC-bias capacitance change rate decreased under a DC field at 40 kV/cm. The optimal component showed a dielectric constant of 2200 and met the requirement of the X8R MLCCs application. Moreover, the outstanding highly accelerated life-time and higher grain boundary activation energy substantiated that Yb dopant prominently improved the reliability of dielectric materials of MLCCs. All these studies provide meaningful recommendations for the research on dielectric materials of high-performance, high-reliability base-metal MLCCs.     

Effect of yttrium (Y) substitution on the structure and dielectric properties of BaTiO3

As the rate of application of multilayer ceramic capacitors (MLCCs) in small electronic devices increases, the use of the raw material barium titanate (BaTiO₃) with a small particle size and excellent dielectric properties becomes needed. Due to the size effect, small-sized BaTiO₃ generally has a cubic phase structure with a low dielectric constant, which limits its use in MLCCs. We report the preparation of small cubic phase Y-doped BaTiO₃ (BYT) nanoparticles by a hydrothermal method and the preparation of highly dielectric tetragonal phase BYT ceramics based on this method. XRD and Raman analysis showed that the BYT nanoparticles are in substable cubic phases. The particle size of the BYT nanoparticles, measured by TEM, XRD, and BET, was approximately 35 nm. The dielectric properties of the BYT ceramics were tested by an impedance analyzer, and the dielectric constant of the BYT ceramics was 7547 when the Y³⁺ doping amount was 0.5 mol%. In addition, the substitution mechanism of Y³⁺ doping in BaTiO₃ crystals was proposed from XPS and EPR analysis. The results demonstrate for the first time that the 50 nm cubic phase BaTiO₃ powder can meet the needs of next-generation high-capacity MLCCs. This work provides a reference for small cubic phase BaTiO₃ as a dielectric material for high-capacity MLCCs.     

Importance of uniformity of grain size to reduce dc degradation and improve reliability of ultra-thin BaTiO3-based MLCCs

Excellent direct current (dc)-bias and reliability have become increasingly important for ultra-thin BaTiO₃-based multilayer ceramic capacitors (MLCCs). Herein, X5R-MLCCs with a thickness of ～1 μm are fabricated using BaTiO₃ with varied grain size. It is shown that the uniformity of the grain size plays an important impact on the direct current (dc)-bias and the reliability of ultra-thin MLCCs. Uniform grain size, which is indicative of good distribution of doping element contributes to improved temperature stability. By contrast, abnormal large grains induce reinforced space charge polarization. Chips with non-uniform grains exhibit dramatic dielectric constant change under dc-bias due to the high tetragonality and irreversible domain-wall motion. Weibull distribution and highly accelerated life test (HALT) reveal that non-uniform grains contain more oxygen vacancies supported by impedance spectra analysis at 300–450 °C. This study provides a feasible strategy to improve the dc-bias and the reliability of the ultra-thin MLCCs.     

The role of diffusion behavior on the formation and evolution of the core-shell structure in BaTiO3-based ceramics

In this work, the influence of starting particle size and sintering conditions on the microstructures and dielectric properties of BaTiO₃-based ceramics coated with 0.3Bi(Zn_1/2Ti_1/2)O₃-0.7BaTiO₃ were investigated to reveal the core-shell structure by using high resolution transmission electron microscopy technique coupled with energy-dispersive spectrometer analysis. The ion-diffusion behavior plays a critical role in the formation and evolution of the core-shell structure and, therefore, significantly influences the dielectric properties. When using starting powders containing BaTiO₃ particles larger than 100 nm in size and sintering for shorter dwelling times (0.5-2.0 hours), a core-shell structure could be formed and retained owing to the limited diffusion behavior, enabling BaTiO₃-based ceramics to meet the X8R specification for multilayer ceramic capacitors applications at high temperatures. However, when using 80 nm BaTiO₃ nanopowders and further extending the dwelling time to 6.0 hours, more driving energy was provided to prompt ion diffusion, which led to the compositional inhomogeneity becoming homogenized.     

Lead-free multilayer ceramic capacitors with ultra-wide temperature dielectric stability based on multifaceted modification

The rapid development of high technology—such as space exploration and electric vehicles—urgently requires ultra-wide temperature multilayer ceramic capacitors (UWT MLCCs) to achieve reliable operation of electronic circuits in harsh environments. However, simultaneously achieving high dielectric permittivity, low dielectric loss, and ultrahigh thermal stability has been a major challenge for practical dielectric ceramics. The co-firing matching of the internal electrode and the dielectric ceramic is also an important factor that affects the reliability of UWT MLCCs. Herein, through multifaceted modification—i.e., composition design related to the modulation of the local polar nanoregions (PNRs) and optimizing device sintering in the context of the compatibility of the heterogeneous interface—these concerns have been well-addressed. A new lead-free dielectric system (1-x) (0.56Na_0.5Bi_0.5TiO₃-0.14K_0.5Bi_0.5TiO₃-0.3NaNbO₃)-xCaZrO₃ (NKBTNN-xCZ) dominated by P4bm PNRs was designed and corresponding UWT MLCCs with reliable Pt internal electrode interface bonding were fabricated by optimizing the sintering temperature. A record-high dielectric permittivity (ε_r = 839 ± 15 %) and low dielectric loss (tanδ ≤0.02) was achieved over an ultra-wide temperature range from -70 °C to 337 °C for NKBTNN-0.063CZ UWT MLCCs. This work suggests that multifaceted modification should be generalized for construction of high-performance UWT MLCCs.     

Exceptional reliability of MLCCs enabled by defect-engineered BaTiO3

It has generally been believed that the reliability of BaTiO₃-based multilayered ceramic capacitors (MLCCs) is mainly contributed by hydroxyl (OH⁻), and the contribution of CO₃²⁻ can be neglected. However, in this work, we demonstrated that the contributions of Ba/Ti ratio and CO₃²⁻ play important roles in the delivering high reliability for BaTiO₃-based MLCCs. The structure and performance of MLCC devices and ceramic chips based on BaTiO₃ powders prepared by different approaches were studied. It is found that the intracrystalline pores in ceramics or MLCCs are mainly derived from the decomposition of BaCO₃ during sintering, which has been demonstrated by ceramic derived from hydrothermal method powder and its modified powders. The point defects of Ba and Ti vacancies mainly originating from nonstoichiometric Ba/Ti rather than thermally stimulated have substantial influence on the migration of grain boundary that determines the grain size and whether the pores can be annihilated from the bulk material. Particularly, the Ti vacancies have a strong pinning effect and inhibit the migration of grain boundary effectively, due to their shorter migration distance comparing to Ba vacancies. Therefore, the synergetic effect of the second phase BaCO₃ and point defects leads to the differences in the structure and performance.     

Fabrication of lanthanum doped BaTiO3 fine-grained ceramics with a high dielectric constant and temperature-stable dielectric properties using hydro-phase method at atmospheric pressure

Lanthanum doped BaTiO₃ powders were synthesized by the hydro-phase method at atmospheric pressure, which controls the uniformity and particle size of the ceramic powders. The effects of La³⁺ ions concentration on the microstructure and dielectric properties of BaTiO₃ ceramics were studied. The results suggested that both the average grain size and dielectric constants (ε_r and ε_max) of the ceramics decreased as the concentration of La³⁺ increased. The ceramic met the X8R specifications: La³⁺ ions concentration of 3 mol%, a permittivity of 2322, low dielectric loss of less than 0.6% at room temperature, and average grain size of about 260 nm.     

Achieving ultrabroad temperature stability range with high dielectric constant and superior energy storage density in KNN–based ceramic capacitors

Multilayer ceramic capacitors (MLCCs) had become an important component of many electronic devices on account of its miniaturization, high capacitance and reliability. To satisfy the requirements of MLCCs, the temperature–insensitivity and dielectric properties of the dielectric ceramics were urgent to be enhanced. In our work, (1–x)K_0.5Na_0.5NbO₃–xBi(Li_0.5Nb_0.5)O₃ (abbreviated to KNN–xBLN) were successfully synthesized by traditional solid state reaction method. On the one hand, the doping BLN induced the diffused phase transition and broadened the dielectric anomaly peaks, which improved the temperature insensitivity of KNN-based ceramics. On the other hand, the nanosized grains and dense microscopy boosted the breakdown electric field. Ultimately, the KNN–0.175BLN samples presented the excellent dielectric properties with high dielectric constant (1735) and low dielectric loss (1.9%) at room temperature with a wide temperature stability range (–62 – 300 °C), which exhibited the wider temperature stability range than X9R specification. Meanwhile, the x = 0.175 samples also achieved a high recoverable energy storage density of 3.71 J/cm³ under the breakdown electric field of 360 kV/cm. The designed KNN–based dielectric materials were expected to be applicable to the energy storage capacitor with standed high operating temperature.     

Effects of Bi4Ti3O12 addition on the microstructure and dielectric properties of modified BaTiO3 under a reducing atmosphere

The effects of Bi₄Ti₃O₁₂ addition on the microstructure and dielectric properties of Mn-modified BaTiO₃ were investigated to develop low temperature fired BaTiO₃-based ceramics with stable temperature characteristics. The sintering temperature of Mn-doped BaTiO₃ could be reduced to 1200 °C by adding more than 1 mol% Bi₄Ti₃O₁₂. TEM results show an apparent core–shell structure with 2 mol% Bi₄Ti₃O₁₂ addition. However, it was destroyed when the Bi₄Ti₃O₁₂ content increased from 2 to 4 mol%. The permittivity decreased and the Curie temperature shifted to higher temperature when the Bi₄Ti₃O₁₂ content increased from 0 to 3 mol%. The temperature characteristic of capacitance was very close to the EIA X8R specification when 2 mol% Bi₄Ti₃O₁₂ was added due to the presence of the core–shell grain structure and raised Curie temperature. With adequate Bi₄Ti₃O₁₂ addition, the BaTiO₃-based system shows great potential for applications in EIA X8R-type multilayer ceramic capacitors.     

A quick method to determine the capacitance characteristics of thin layer X5R multilayer capacitors

The effect of Y₂O₃ concentration on the dielectric properties of ceramic disc capacitors and multilayer capacitors containing 50 dielectric layers with an approximate thickness of 3 μm were investigated. The relative permittivity and temperature coefficient of capacity of multilayer capacitors at low and high applied field suggest that two types of microstructures formed, depending on yttrium doping concentration. Yttrium concentrations of 1.5-2.0 mol% yielded identical relative permittivities over a wide temperature range. The permittivities at Y concentrations of 2.6-3.0 mol% were also identical, but somewhat higher. The relative permittivity of ceramic disc capacitors of similar composition, determined from hysteresis loop measurements as function of applied field, was compared with field-dependent permittivity measurements on multilayer capacitors. The results indicate that polarization measurements on CDCs are a good indicator for the relative permittivity values of MLCCs.     

Duplex structure in K0.5Na0.5NbO3-SrZrO3 ceramics with temperature-stable dielectric properties

Temperature-stable dielectric properties have been developed in the 0.86 K_0.5Na_0.5NbO₃-0.14SrZrO₃ solid solution system. High dielectric permittivity (ε′ = 2310) with low loss sustained in a broad temperature range (−55–201 °C), which was close to that of the commercial BaTiO₃-based high-temperature capacitors. Transmission electron microscopy with energy dispersive X-ray analysis directly revealed that submicron grains exhibited duplex core-shell structure. The outer shell region was similar to the target composition, whilst a slightly poor content of Sr and Zr presented in the core region. Based on Lichtenecker’s effective dielectric function analysis along with Lorentz fit of the temperature dependence of dielectric permittivity, a plausible mechanism explaining the temperature-stable dielectric response in present work was suggested. These results offer an opportunity to achieve the X8 R specification high-temperature capacitors in K_0.5Na_0.5NbO₃ based materials.     

Synthesis and performance of tetragonal BaTiO3 fine powders via a facile tartaric acid assisted method

A facile tartaric acid assisted method using metatitanic acid, barium hydroxide and tartaric acid as starting materials is proposed to prepare tetragonal BaTiO₃ fine powders. Owing to the ultrafine character of the as-formed BaCO₃ with high chemical activity, and its arrangement coating the surface of intermediate TiO₂ nanoscale needles, pure cubic phase BaTiO₃ homogeneous powders with size of about 50 nm was obtained via calcining treatment at 650 ℃, which subsequently transformed as tetragonal BaTiO₃ uniform powders with size of about 240 nm and high tetragonality (c/a=1.0095) after calcining treatment at 1050 ℃. The BaTiO₃ ceramic prepared from the BaTiO₃ uniform powders displayed much improvement performances with high permittivity of about 5980 and low dielectric loss of about 0.014 at room temperature in comparison to the BaTiO₃ ceramic prepared respectively from the BaTiO₃ synthesized via a traditional solid-state method, and commercial BaTiO₃, suggesting it’s compatible in application of MLCCs with high performance.     

Structure and dielectric properties of barium titanate thin films for capacitor applications

BaTiO₃ is a typical ferroelectric material with high relative permittivity and has been used for various applications, such as multilayer ceramic capacitors (MLCCs). With the tendency of miniaturization of MLCCs, the thin films of BaTiO₃ have been required. In this work, BaTiO₃ thin films have been deposited on Pt-coated Si substrates by RF magnetron sputtering under different deposition conditions. The films deposited at the substrate temperature from 550 °C–750 °C show a pure tetragonal perovskite structure. The films deposited at 550 °C–625  °C exhibit (111) preferential orientation, and change to (110) preferential orientation when deposited above 650 °C. The film morphologies vary with working pressure and substrate temperature. The film deposited at 625 °C and 4.5 Pa has the relative permittivity of 630 and the loss tangent of 2% at 10 kHz.     

Investigation of thin film end-termination on multilayer ceramic capacitors with base-metal-electrode

The thin film of copper, chromium and titanium as end-termination studies were performed on multilayer ceramic capacitors (MLCCs) based on BaTiO₃ ceramic with nickel internal electrodes. A green sheet was prepared by tape casting using the X7R/BME powders. Nickel paste was attached to the green sheet as an internal electrode. After lamination, the green chips were sintered at 1300 °C for 2 h, then the external electrodes were sputtered as thin films for end-termination. There is no extra curing process, so that thermal shock of the MLCCs is reduced. To improve the adhesion between thin film end-termination and dielectric body, chromium and titanium were applied as media in this study. The mechanical and electrical properties of the MLCCs were investigated subsequently. The results showed that end-termination with chromium/copper has good performances on electrical and mechanical properties of MLCC, compared to conventional end-termination.     

The formation of Y5V-type fine-grained ceramics based on spherical submicron BaZr0.1Ti0.9O3@Al2O3 particles

To improve multilayer ceramic capacitors (MLCCs), thinner dielectric layers are necessary. To achieve this goal, both grain size and uniformity of the MLCC particles must be controlled effectively. In this study, the core-shell structure of submicron-sized multi-function ceramic capacitors powder was synthesized using a novel precipitation route, which controls both dispersion and particle size of BaZr_0.1Ti_0.9O₃ and BaZr_0.1Ti_0.9O₃@Al₂O₃ particles. In this paper, we investigate the effect of Al₂O₃ coating on the microstructure and the dielectric properties of BaZr_0.1Ti_0.9O₃. We found that both average grain size and maximum dielectric constant (ε_max) of the ceramics decrease with increasing concentration of Al₂O₃. Our results demonstrate that fine-grained ceramic materials can meet the specifications of the Electronic Industries Alliance Y5V with a concentration of Al₂O₃-coated of 0.25 mol percent, a permittivity of 3393 at room temperature, and an average particle size of about 400 nm.     

Influence of A‐site nonstoichiometry on the electrical properties of BT‐BMT

A stoichiometric and 2 mol% Ba deficient samples in the formulation 0.5BaTiO₃‐0.5BiMg_1/2Ti_1/2O₃ (BT‐BMT) were processed via a mixed oxide solid‐state route. The deficient sample exhibited a high relative permittivity (2100±15%) over the temperature range 90‐450°C and a low dielectric loss (tanδ < 0.01), maintained up to high temperature (430°C). The samples exhibited intrinsic conduction mechanism and showed an n‐type character. By introducing 2 mol% Ba vacancies, a dramatic influence on the dielectric loss was observed which was mainly associated with the trapping of electrons by barium‐oxygen vacancy pair associated with the intentionally produced cation vacancies. Thus, control of composition by creating deficiency allows fine tuning of the dielectric properties of BT‐BMT ceramics for applications in high‐temperature multilayered ceramic capacitors.     

Fabrication of BaTiO3-PTFE composite film for embedded capacitor employing aerosol deposition

The potential for using aerosol deposition (AD) as an alternative fabrication method to the conventional polymer composite process for embedded capacitors was examined. In order to achieve a high relative dielectric permittivity, BaTiO₃-polytetrafluoroethylene (PTFE) composite thick films were attempted by AD at room temperature. For the high dielectric constant, the BaTiO₃-PTFE composite films grown by AD should satisfied the following two critical conditions: a reduced decrement in ceramic particle size and a relieved distortion of the crystal structure. However, the relative permitivity of the composite films was too low compared with that of the BaTiO₃ films grown by AD. By predicting the dielectric constant in several composite models using the Hashin-Shtrikman bounds theory and 3-dimenstional (3-D) electrostatic simulation, we confirmed that the connectivity between ceramic particles is a highly critical factor for achieving a high dielectric constant in composite films.     

Superior temperature‐stable dielectrics for MLCCs based on Bi0.5Na0.5TiO3‐NaNbO3 system modified by CaZrO3

An ultra‐wide temperature stable ceramic system based on (1?x) [0.94(0.75Bi_0.5Na_0.5TiO₃?0.25NaNbO₃)?0.06BaTiO₃]?xCaZrO₃ (CZ100x) is developed for capacitor application in this study. All samples exhibit characteristics of pseudocubic structures in XRD patterns. With CaZrO₃ addition, the coupling effect of polar nanoregions (PNRs) is weakening, leading to greatly improved temperature stability of dielectric properties. Among all samples, the most attractive properties are obtained in the composition of CZ10 at <15% variation in dielectric permittivity spanning from ?55°C to 400°C and lower than 0.02 of dielectric loss of between ?60°C and 300°C, accompanied by high DC resistivity (10⁷ Ω m at 300°C, calculated by fitting Jonscher's power law). Furthermore, tentative multilayer ceramic capacitors (MLCCs) composed of CZ10 dielectric and Ag:Pd (70:30) internal electrode layers were fabricated by tape casting and cofiring processes. Temperature‐stable dielectric property in formation of MLCC was successfully realized, with small ΔC/C_25°C (<15%) and loss factor (≤ 0.02) between ?55°C and 340°C. Meanwhile, CZ10‐based MLCC showed temperature‐insensitive energy storage density of 0.31?0.35 J/cm³ and high‐energy efficiency of above 77% at 120 kV/cm in the range of ?55 to 175°C. All of these exhibit wonderful temperature‐stable dielectric properties and indicate the promising future of CZ10 dielectric as high‐temperature ceramic capacitors.