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).     

Role of A-site (Sr), B-site (Y), and A,B sites (Sr,Y) substitution in lead-free BaTiO3 ceramic compounds: Structural,optical, microstructure,mechanical, and thermal conductivity properties

Strontium and Yttrium-doped and co-doped BaTiO₃ (BT) ceramics with the stoichiometric formulas BaTiO₃, B_1-xSr_xTiO₃, Ba_1-xY_xTiO₃, BaTi_1-xY_xO₃, Ba_1-xY_xTi_1-xY_xO₃, and Ba_1-xSr_xTi_1-xY_xO₃ (x = 0.075) noted as BT, BSrT, BYT, BTY, BYTY, and BSrTY have been synthesized through sol-gel method. X-ray diffraction (XRD) patterns of the prepared ceramics, calcined at a slightly low temperature (950 °C/3h), displayed that BT, BSrT, and BYT ceramics possess tetragonal structures and BTY, BYTY, and BSrTY have a cubic structure. The incorporation of the Ba and/or Ti sites by Sr²⁺ and Y³⁺ ions in the lattice of BaTiO₃ ceramic and the behaviors of the crystalline characteristics in terms of the Y and Sr dopant were described in detail. The scanning electron microscopy (SEM) images demonstrated that the densification and grain size were strongly related to Sr and Y elements. UV–visible spectroscopy was used to study the optical behavior of the as-prepared ceramic samples and revealed that Sr and Y dopants reduce the optical band gap energy to 2.74 eV for the BSrTY compound. The outcomes also demonstrated that the levels of Urbach energy are indicative of the created disorder following the inclusion of Yttrium. The measurements of the thermal conductivity indicated the influence of the doping mechanism on the thermal conductivity results of the synthesized samples. Indeed, the thermal conductivity of BaTiO₃ is decreased with Sr and Y dopants and found to be in the range of 085–2.23 W.m^-1. K^?1 at room temperature and decreases slightly with increasing temperature from 2.02 to 0.73-W.m^-1. K^?1. Moreover, the microstructure and grains distribution of the BT, BSrT, BYT, BTY, BYTY, and BSrTY samples impacted the compressive strength, hence; the compressive strength was minimized as the grain size decreased.     

Mechanism of improvement of resistance degradation in Y-doped BaTiO3 based MLCCs with Ni electrodes under highly accelerated life testing

The mechanism of improvement of resistance degradation in Y-doped BaTiO₃ based multilayer ceramic capacitors (MLCCs) with Ni electrodes has been studied using electrical measurement techniques, minor phase identification and the measurement of oxygen vacancy concentration. Admittance spectroscopy and thermally stimulated current measurements show the relaxation due to barium vacancy states caused by Y doping. The minor phase identification by XRD indicated those Y³⁺ substitutes for perovskite A-site. Oxygen vacancy concentration measurement indicated that Y decreases the oxygen ion vacancy concentration in BaTiO₃. These results suggest that Y³⁺ acts as a donor and creates barium vacancies, which compensate for the oxygen vacancies and thereby improve the resistance degradation.     

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.     

A novel route to produce BaTiO3 glass-ceramics with nanosized cubic BaTiO3 phase precipitating for high energy-storage applications

To meet requirements of miniaturization devices in high pulsed power technology, super dielectric energy storage performance, such as high dielectric breakdown strength (DBS), large energy storage density with high power density, is extremely important in dielectric materials. However, for BaTiO₃ based ceramics and glass ceramics, there is still a critical challenge to achieve high DBS and large energy storage density. Herein, a novel route was proposed to precipitate nanocrystals with cubic BaTiO₃ phase from glass matrix, which can elevate dielectric constant and meanwhile maintain high DBS compared to parent glass. A high recoverable energy storage density of ∼ 3.66 J cm⁻³ at 1000 kV cm⁻¹ and high discharge energy density of ∼3.57 J cm⁻³ with good thermal stability and ultra-high peak power density of ∼ 910 MW cm⁻³ can be achieved in BaTiO₃ glass ceramic, which implies this type of glass ceramics is suitable for high pulsed power technology application.     

The characterization of the barium titanate ceramic powders prepared by the Pechini type reaction route and mechanically assisted synthesis

BaTiO₃ ceramic powders were prepared by a complex method based on the Pechini type reaction route and mechanically assisted synthesis. In both ways BaTiO₃ ceramics were sintered after 120 min on 1300 °C without pre-calcination steps. The crystal structure was investigated by the XRD, IR and Raman spectroscopy. The particle size and morphology of BaTiO₃ were examined by XRD and SEM. The XRD results of powders indicate the formation of cubic phase of BaTiO₃. It can be observed that in the case of Pechini process BaTiO₃ powder is well crystallized but in the case of mechanochemistry process, significant amount of amorphous phase was detected. The sintered BaTiO₃ ceramic sample prepared by Pechini process, shows the formation of tetragonal phase. However, IR and Raman spectrum showed a mixture of cubic and tetragonal for BaTiO₃ obtained by Pechini process and tetragonal for BaTiO₃ obtained by mechanically assisted synthesis.     

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.     

Local Structure Investigation in Multiferroic BiFeO3–BaTiO3 Ceramics by XAS Technique and Their Relevant Properties

The (1?x)BiFeO₃‐xBaTiO₃ (with x = 0.1, 0.2, 0.3, and 0.4) ceramics were fabricated successfully by solid‐state reaction method. Single‐phase perovskite was obtained in all ceramics, as confirmed by XRD technique. It was observed that 0.7BiFeO₃–0.3BaTiO₃ was the morphotropic phase boundary (MPB) between rhombohedral and cubic phases, as also revealed from ferroelectric and magnetic properties. The simulated and experimental X‐Ray Absorption Spectroscopy (XAS) study revealed that BT in 0.75BF‐0.25BT is possibly taken a rhombohedral structure. Furthermore, the rounded ferroelectric hysteresis loops observed for 0.9BiFeO₃–0.1BaTiO₃ and 0.8BiFeO₃–0.2BaTiO₃ compositions could be attributed to their microstructure and surface charge effects and electron transfer between Fe³⁺ and Fe²⁺ ions. It was also found that high dielectric constant of 0.9BiFeO₃–0.1BaTiO₃ composition was a result of grain and grain‐boundary effects, as observed in SEM micrographs. In addition, a strong signature of dielectric relaxation behavior was observed in this ceramic system with the activation energy 0.467 eV obtained from the Arrhenius' law. Finally, the local structure investigation with XAS technique provided additional information to better understand the electric and magnetic properties in the BF‐BT ceramic system.     

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.     

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.     

The dielectric property and phase transition of Sr-doping effect of Ba1−xSrxTi0.9Mn0.1O3-δ ceramic

In this work, we prepare Ba_1−xSr_xTi_0.9Mn_.01O_3-δ (x = 0.00, 0.01, 0.03, 0.05, and 0.07) ceramics by the mixed oxide method and study the relationship between phase transition and dielectric property of the ceramics. The phase of the samples transformed from a hexagonal phase to mixed phases due to the increase in Sr doping amount. The X-ray diffraction (XRD) profiles and Raman spectra of the samples also show the same phase transformation due to increasing Sr doping amount. The XRD pattern of the undoped sample indicates a single h-BaTiO₃ phase with P6₃/mmc symmetric space group, while the samples with high Sr doping amounts have a mixed phase with t-BaTiO₃ with P₄mm symmetric space group. The scanning electron microscopy images show two types of BaTiO₃ grains, which grew with increasing sintering temperature. With increasing Sr concentration, the K-values (relative dielectric constant) of the ceramics increased, while the Q_xf values (the quality factor multiplied by frequency) decreased, which indicate that the microwave dielectric property is related to phase transformation.     

Structure Stability and Microwave Dielectric Properties of (1 − x) Ba(Mg1/2W1/2) O3 + xBa(Y2/3W1/3)O3 Ceramics

The structure stabilities of double perovskite ceramics‐ (1 ? x) Ba(Mg_1/2W_1/2)O₃ + xBa(Y_2/3W_1/3)O₃ (0.01 ≤ x ≤ 0.4) have been studied by X‐ray powder diffraction (XRD), scanning electron microscopy (SEM), and Raman spectrometry in this study. The microwave dielectric properties of the ceramics were studied with a network analyzer at the frequency of about 8–11 GHz. The results showed that all the compounds exhibited face‐centered cubic perovskite structure. Part of Y³⁺ and W⁶⁺ cations occupied 4a‐site and the remaining Y³⁺ and Mg²⁺ distributed over 4b‐site, respectively, and kept the B‐site ratio 1:1 ordered. Local ordering of Y³⁺/Mg²⁺ on 4b‐site and Y³⁺/W⁶⁺ cations on 4a‐site within the short‐range scale could be observed with increasing Y‐doping content. The decomposition of the double perovskite compound at high temperature was successfully suppressed by doping with Y on B‐site. However, Ba₂Y_0.667WO₆ impurity phase appeared when x > 0.1. The optimized dielectric permittivity increased with the increase in Y doping. The optimized Q × f value was remarkably improved with small amount of Y doping (x ≤ 0.02) and reached a maximum value of about 160 000 GHz at x = 0.02 composition. Further increasing in Y doping led to the decrease in Q × f value. All compositions exhibited negative τ_f values. The absolute value of τ_f decreased with increasing Y‐doping content. Excellent combined microwave dielectric properties with ε_r = 20, Q × f = 160 000 GHz, and τ_f = ?21 ppm/°C could be obtained for x = 0.02 composition.     

Characteristics of Ag-doped BaTiO3 nanopowders prepared by spray pyrolysis

Pure and Ag-doped BaTiO₃ nanopowders were prepared by spray pyrolysis. Precursor powders, prepared from a spray solution with citric acid and ethylenediaminetetraacetic acid (EDTA) as chelating agents, had large, hollow particles irrespective of Ag doping. Both pure and Ag-doped powders had partially aggregated particles after post-treatment at 900 °C that could be easily milled to nanoparticles. The mean sizes of the pure and Ag-doped BaTiO₃ particles were 75 and 91 nm, respectively. The Ag-doped particles were mainly of cubic BaTiO₃ crystal structure, with small Ag phases observed. High-density BaTiO₃ pellets were formed by sintering the powders at the low temperature of 1000 °C. The silver was uniformly distributed in a tetragonal BaTiO₃ phase without phase separation in the doped pellet. The dielectric constants of the pellets formed from the pure and Ag-doped BaTiO₃ powders were 1826 and 2400, respectively.     

Effect of BiMO3 (M=Al,In, Y,Sm, Nd,and La) doping on the dielectric properties of BaTiO3 ceramics

In this study, in order to enhance the energy storage density, 10% BiMO₃ doping is performed in BaTiO₃ ceramics (M=Al, In, Y, Sm, Nd, La) by a traditional solid-state method. The effects of different M³⁺ radii on the structural characteristics, dielectric properties, and energy storage are investigated systematically. The locations of the M-ions gradually shift from B-site substitutions to A-site substitutions with the increase in the ionic radius, which affect the structural characteristics and the dielectric properties. When 80<R_M3+<95.5 pm, the ceramic has a cubic phase which shows the highest energy density; while out of this range, the dielectric properties of the ceramics are degraded. Specially, the change rate of permittivity of the Sm substituted composition reaches 70% at 100 kV/cm, which might be good for high frequency tunable device application. Typically, combined with the suppression of nonlinearity, polarization maximum (P_m) and remnant polarization (P_r), 0.9BaTiO₃–0.1BiInO₃ exhibits the maximum energy density of 0.753 J/cm³ and the highest energy efficiency of 89.4%, which exhibits slim P-E hysteresis loops for energy storage applications.     

Improved Energy Storage Properties of Fine‐Crystalline BaTiO3 Ceramics by Coating Powders with Al2O3 and SiO2

The multilayer structure of capacitor demands for fine grain size of dielectric ceramics in devices, because the thinner layer which needs ceramics with fine grain size is helpful in enlarging the capacitance. In this paper, the aqueous chemical coating method was utilized to modify the BaTiO₃ particles. The fine‐crystalline BaTiO₃ ceramics with an average grain size below 200 nm without abnormal grain growth by co‐coating Al₂O₃ and SiO₂ has been prepared. The phase composition, microstructures of coated particles and ceramics, and dielectric properties were investigated. For samples containing 3 wt% of Al₂O₃ and 1 wt% of SiO₂, the energy storage density is 0.725 J/cm³ and the efficiency of the ceramic samples can keep above 80%. The breakdown strength was improved to about 190 kV/cm.     

Formation and Accumulation of Intragranular Pores in the Hydrothermally Synthesized Barium Titanate Nanoparticles

As highly integrated circuits are demanded for high‐performance electric devices, small sizes of barium titanate (BaTiO₃) as a dielectric material are desirable for the application of multilayer ceramic capacitors. Since the small sizes of the particles degrade the dielectric property, especially below a certain critical size, understanding the probable cause is significant for the high‐performance capacitors. Here, we have demonstrated nanosized BaTiO₃ with average size below 30 nm and a uniform size distribution. High‐resolution transmission electron microscopy (TEM) shows that the as‐synthesized BaTiO₃ contains intragranular pores. We have analyzed the correlation between the intragranular pores inside nanoparticles and their phase ratio of cubic and tetragonal. We have found that the presence of the intragranular pores affects low tetragonality of BaTiO₃ particles, and the intragranular pores are generated by the accumulation of hydroxyl groups during hydrothermal reaction. Formation and accumulation of intragranular pores have been investigated by ex‐situ synchrotron X‐ray diffraction and TEM analysis, suggesting the phase evolution model of nanosized BaTiO₃.     

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.     

Hydrothermal synthesis of pseudocubic BaTiO3 nanoparticles using TiO2 nanofibers: Study on photocatalytic and dielectric properties

In this study, TiO₂ nanofibers were fabricated via the electrospinning method followed by air annealing. Then, Ti-requirement in the conventional hydrothermal synthesis of BaTiO₃ stoichiometry was supplied by using these nanofibers. The microstructural and compositional properties of BaTiO₃ nanoparticles were studied using SEM, TEM, XRD, XPS, and Raman spectroscopy. The structural analysis showed that the cubic symmetry was the dominant one in the BaTiO₃ nanoparticles, whereas Raman spectroscopy indicated the coexistence of cubic symmetry with the tetragonal polymorph. The nanoparticles displayed higher photocatalytic reactivity under UV-A light compared to visible irradiation during decomposition of methylene blue dye and reached 24.2% and 18.8% degradation, respectively, after 1 hour. Furthermore, the dielectric properties were investigated using sintered compacts of these nanoparticles. Among the employed temperatures for sintering, the highest relative density (90%) and dielectric constant (2165 at 1 MHz) were obtained at 1250°C and 5 hours. This study revealed that the electrospun TiO₂ nanofiber precursor can successfully be used for the production of nanoscale barium titanate particles suitable for various applications.     

The Occupation Behavior of Y2O3 and Its Effect on the Microstructure and Electric Properties in X7R Dielectrics

The occupation behavior of Y₂O₃ in nonreducible BaTiO₃‐based ceramics was investigated thoroughly. Based on XRD, SEM, TEM‐EDS, and complex impedance analysis, it is ensured that there exists two turning points of Y₂O₃, 0.50 mol% and 1.00 mol%, and the latter is the solubility limit. Below 0.50 mol%, the introduced Y³⁺ ions precede to enter the A sites of the perovskite lattice, causing an observed enhancement in dielectric constant and energy storage density accompanied by an increase in grain size. Once the addition exceeds 0.50 mol%, the Y³⁺ ions will turn to occupy B sites to substitute for Ti⁴⁺ ions, leading to the significant reduction in dielectric constant and energy storage density. Above the solubility limit of 1.00 mol%, the excess Y³⁺ ions would segregate at grain boundary and even induce the formation of Y₂Ti₂O₇ phase, resulting in an abrupt enhancement of grain‐boundary resistance. Doped with 0.75–1.50 mol% Y₂O₃, all nonreducible specimens meet X7R requirement.