Dielectric Ceramics Research Articles

New microwave dielectric ceramics based on the CaRNbWO8 (R = Y, La, Ce, Nd or Sm) system

New microwave dielectric ceramics based on the CaRNbWO8 (R = Y, La, Ce, Nd or Sm) system

Effect of sintering temperature on properties of Ba (Cu1/2W1/2) O3 high dielectric ceramics

Effect of sintering temperature on properties of Ba (Cu1/2W1/2) O3 high dielectric ceramics

Molybdenum oxide reinforced polyvinyl alcohol composite as high-performance dielectric material for flexible electronics

Polymer dielectrics are highlighted as capable energy storing materials due to their better dielectric strength and supreme versatility compared to inorganic ceramic dielectrics in sophisticated electronics and pulsed power systems. The capacity of pristine polymers to store energy, on the other hand, has hardly been constrained by relatively poor internal dielectric properties. This study demonstrates a viable solution-casting method for creating a MoO3 (0%, 1%, 3%, and 5%) doped PVA-based composites for notable dielectric characteristics. The structural variations and morphological properties in the presence of MoO3 nanoparticles within the polymer, connected through intra/intermolecular hydrogen bonding are investigated using XRD and FTIR. The influence of MoO3 content on the complex dielectric properties, conductivities, electric modulus, and impedance parameters of PVA is further investigated. According to the MoO3 proportion in the host matrix, the dielectric properties and relaxation factors associated with polymer cooperative chain segmental migration alter considerably. The improved electrical and dielectric properties of MoO3 doped PVA composite demonstrate its potential in creating compact polymer electrolyte systems.

Superior energy storage capacity of a Bi0.5Na0.5TiO3-based dielectric capacitor under moderate electric field by constructing multiscale polymorphic domains

The challenge of electronic components failing in service when exposed to ultra-high electric fields necessitates the development of dielectric capacitors with a higher energy storage density per electric field. Therefore, the development of dielectric capacitors with high energy storage density under moderate electric fields is of great importance. To address this issue, a polymorphic multiscale domain construction strategy has been proposed in this work. Guided by the results of phase field simulations, lead-free Bi0.5Na0.5TiO3-Sr0.7Bi0.2TiO3-La(Mg0.5Ti0.5)O3 ceramics have been prepared, which enable the coexistence of rhombohedral (R) + tetragonal (T) nanodomains and polar nanoregions (PNRs). This has resulted in a total energy density of 7.3 J·cm−3 and efficiency of 93% at 390 kV·cm−1 in the current system. Additionally, the energy storage potential (Wrec/Eb) of this ceramic is the highest in Bi0.5Na0.5TiO3-based systems among the latest research. Furthermore, the ceramic displays excellent thermal stability from − 50 to 200 ℃. This work provides a new approach to enhance the energy storage properties (ESPs) of dielectric ceramics under moderate electric fields.

Crystal structure, far-infrared spectroscopy, and microwave dielectric properties of two novel vanadates CaRECeV3O12 (RE = Nd, Sm)

Two novel low-εr CaRECeV3O12 (RE = Nd, Sm) microwave dielectric ceramics were prepared to utilize the solid-state method. According to XRD and Raman spectroscopy data, the CaRECeV3O12 (RE = Nd, Sm) ceramics had a tetragonal zircon-type with an I41/amd space group. Dense CaNdCeV3O12 and CaSmCeV3O12 ceramics sintered at 1225 °C and 1200 °C showed εr ∼11.85 ± 0.1 and 11.33 ± 0.1, Q × f ∼40,100 ± 500 GHz and 43,290 ± 500 GHz, τf ∼ −27.2 ± 0.5 ppm/°C and −22.4 ± 0.5 ppm/°C, along with αL of 9.4 ppm/°C and 8.5 ppm/°C, respectively. The measured εr and corrected εr(corr) values were larger than εr(C-M) (9.41 and 9.47) in CaNdCeV3O12 and CaSmCeV3O12 due to the cations being, on average, under-bonded and the overall structures being in a slightly expanded state. The slightly higher |<d>| value of CaNdCeV3O12 led to its higher εr(corr) value, even though it had a lower αD/Vm value. The sign and magnitude of τf values for CaNdCeV3O12 and CaSmCeV3O12 were mainly determined by their positive temperature coefficients of dielectric polarizability ταm of +36.2 ppm/°C and +32.1 ppm/°C, respectively. The inherent dielectric constant and dielectric loss were examined using far-infrared reflectivity spectra, Raman spectra, and the packing fraction.

Lead-free KNN-based ceramics incorporated with Bi(Zn2/3Nb1/3)O3 possessing excellent optical transmittance and superior energy storage density

The application of lead-free dielectric ceramics for energy storage has received extensive attention because of their remarkable potential as pulse capacitors in power electronic devices. The current study developed a strategy for improving the energy storage performance of (K0.5Na0.5)NbO3 (KNN)-based ceramics by incorporating Bi(Zn2/3Nb1/3)O3 to reduce grain size, increase dielectric breakdown strength, and enhance ferroelectric relaxation degree. The resulting 0.87KNN–0.13BZN ceramics exhibited a high energy density (7.4 J/cm3) and moderate energy efficiency (74%) at an ultrahigh electric field (750 kV/cm) as well as excellent optical properties. Therefore, the 0.87KNN–0.13BZN ceramic is a promising candidate for pulse capacitors, providing a feasible approach for the development of new lead-free energy storage materials.

NaYW2O8: A novel glass-free microwave dielectric ceramic for LTCC application

Microwave dielectric ceramics are important materials for wireless communication devices because of their excellent dielectric properties. Tungstenate compounds with multiple scheelite structures can be used in low temperature co-fired ceramic (LTCC) devices because of their low densification temperature and high-quality factor. In this study, NaYW2O8 ceramics (NYW) were synthesized by a solid-state reaction method at a low densification temperature below the Ag melting point. The microstructure, morphology and microwave dielectric properties of NYW ceramics were investigated, and the effects of packing fraction and lattice energy on microwave dielectric properties were studied. The results showed that the microwave dielectric properties of NYW ceramics were influenced by the grain size and porosity, and deteriorated with the increase of porosity. In addition, the stacking fraction and lattice energy shared a similar trend with the quality factor. The NYW ceramics sintered at 925 °C exhibited excellent microwave dielectric properties with εr= 10.8, Q × f = 49,800 GHz (at 10.5 GHz), and τf= −26.5 ppm/°C. In particular, the NYW ceramics were found to have an excellent chemical compatibility with Ag. The above results indicate the NYW ceramics are candidate in LTCC applications.

Effect of Nb5+ doping on microwave dielectric properties of MgTa2O6 ceramic

As the main carrier for microwave circuits, microwave dielectric ceramics are receiving a lot of attention as the main carrier for the current 5G and pre-developed 6G communication technologies. A series of Nb5+ doped MgTa2O6 ceramics were synthesized by the solid-state reaction method X-ray diffraction confirmed that a single tetragonal structure can be formed when the doping amount is lower than 0.03, a heterogeneous structure of tetragonal and orthorhombic crystal structure is formed when the doping amount is lower than 0.15, and the tetragonal structure is completely transformed into orthorhombic structure when the doping exceeds 0.15. SEM results also show the transformation process of the grains of tetragonal structure to orthorhombic structure. The optimum microwave dielectric properties were obtained for 9% Nb5+ doped samples: εr = 24, Q×f = 71,000 GHz (at 8.9 GHz), TCF = 15 ppm/oC.

Recent progress in dielectric resonator antenna: Materials, designs, fabrications, and their performance

Dielectric resonator antenna (DRA) has secured an esteemed position in the field of antenna engineering technology due to its versatile features, including compactness, light-weight, low loss, high radiation efficiency, ease of excitation, diverse feeding techniques, multiple excitation modes, ease of integration with passive and active microwave integrated circuit components, a wide variety of available materials, simple fabrication techniques, and high degree of flexibility over wide frequency range. This article presents a comprehensive up-to-date review of research carried out in the field of DRA technology which includes an overview of DRA technology, its history, present status, and prospects. The basic parameters of microwave dielectric ceramic materials and the classification of materials based on utilization and material parameters are briefly discussed. The applications of DRA in different fields of science, engineering, and technology, overview of different reported DRA shapes, and the feeding techniques used to excite different modes of DRA are mentioned. Based on the control of DRA permittivity, shape/geometry, feeding techniques, and structural modifications, performance parameters engineering of DRA and its achievable performance in terms of low profile, compactness, high gain, wide beam, circular polarization, wide bandwidth, DRA decoupling methods for multiple input multiple output arrays, dielectric patch antenna, filtering DRA, and reconfigurable DRA are discussed. Different techniques used to attain and enhance the particular performance of DRA are highlighted. This review article also dilates upon the fabrication processes and characterization methods of DRA microwave dielectric ceramics, which play a very vital role in controlling the performance and properties of DRA.

Excellent thermal stability and high energy storage performances of BNT-based ceramics via phase-structure engineering

Herein, a novel strategy for regulating the phase structure was used to significantly enhance the recoverable energy storage density (Wrec) and the thermal stability via designing the (1-x)[(Bi0.5Na0.5)0.7Sr0.3TiO3]-xBiScO3 ((1-x)BNST-xBS) relaxor ferroelectric ceramics. The incorporation of BS into BNST ceramics markedly increases the local micro-structure disorder, causing a high polarization and inhibiting polarization hysteresis for 0.95BNST-0.05BS ceramics, leading to a large Wrec of 5.41 J/cm3 with an ideal efficiency (η) of 78.5%. Meanwhile, transmission electron microscope (TEM) results further proved that the nano-domain structure and the tetragonal (P4bm) phase superlattice structure of 0.95BNST-0.05BS ceramics possess an excellent thermal stability (20–200 °C). An outstanding Wrec value of 3.18 × (1.00 ± 0.03) J/cm3 and an η value of 74.500 ± 0.025 are achieved under a temperature range from 20 °C to 200 °C. This work provides a promising method for phase-structure design that can make it possible to apply temperature-insensitive ceramic dielectrics with a high energy storage density in harsh environments.

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)K0.5Na0.5NbO3–xBi(Li0.5Nb0.5)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.

The Enhanced Thermal Stability of (Mg0.95Ni0.05)2TiO4 Dielectric Ceramics Modified by a Multi-Phase Method.

The thermal stability of (Mg0.95Ni0.05)2TiO4 dielectric ceramics has been improved by mixing with CaTiO3 phases owing to higher positive temperature coefficients. The pure (Mg0.95Ni0.05)2TiO4 and the mixture phase systems of CaTiO3-modified (Mg0.95Ni0.05)2TiO4 were verified by XRD diffraction patterns to ensure the crystallite of different phases. The microstructures of the CaTiO3-modified (Mg0.95Ni0.05)2TiO4 were observed by SEM and EDS to investigate the relation between element ratios and grains. As a result, it can be seen that the thermal stability of the CaTiO3-modified (Mg0.95Ni0.05)2TiO4 can be effectively enhanced, compared with the pure (Mg0.95Ni0.05)2TiO4. Moreover, the radio frequency dielectric performances of CaTiO3-modified (Mg0.95Ni0.05)2TiO4 dielectric ceramics are strongly dependent upon the density and the morphology of the specimens. The champion sample with the ratio of (Mg0.95Ni0.05)2TiO4 and CaTiO3 of 0.92:0.08 showed an εr value of 19.2, an Qf value of 108,200 GHz, and a τf value of -4.8 ppm/°C, which may encourage (Mg0.95Ni0.05)2TiO4 ceramics to broaden the range of novel applications and match the requirements of 5G or next-generation communication systems.

Texture Engineering Modulating Electromechanical Breakdown in Multilayer Ceramic Capacitors

Understanding the electromechanical breakdown mechanisms of polycrystalline ceramics is critical to texture engineering for high-energy-density dielectric ceramics. Here, an electromechanical breakdown model is developed to fundamentally understand the electrostrictive effect on the breakdown behavior of textured ceramics. Taking the Na0.5 Bi0.5 TiO3 -Sr0.7 Bi0.2 TiO3 ceramic as an example, it is found that the breakdown process significantly depends on the local electric/strain energy distributions in polycrystalline ceramics, and reasonable texture design could greatly alleviate electromechanical breakdown. Then, high-throughput simulations are performed to establish the mapping relationship between the breakdown strength and different intrinsic/extrinsic variables. Finally, machine learning is conducted on the database from the high-throughput simulations to obtain the mathematical expression for semi-quantitatively predicting the breakdown strength, based on which some basic principles of texture design are proposed. The present work provides a computational understanding of the electromechanical breakdown behavior in textured ceramics and is expected to stimulate more theoretical and experimental efforts in designing textured ceramics with reliable electromechanical performances.

Novel Method to Achieve Temperature-Stable Microwave Dielectric Ceramics: A Case in the Fergusonite-Structured NdNbO4 System.

Microwave dielectric ceramics with permittivity (εr) ∼ 20 play an important role in massive multiple-input multiple-output (MIMO) technology in 5G. Although fergusonite-structured materials with low dielectric loss are good candidates for 5G application, tuning the temperature coefficient of resonant frequency (TCF) remains a problem. In the present work, smaller V5+ ions (rV = 0.355 Å, with coordination number (CN) = 4) were substituted for Nb5+ (rNb = 0.48 Å with CN = 4) in the Nd(Nb1-xVx)O4 ceramics, which, according to in situ X-ray diffraction data, lowered the fergusonite-to-scheelite phase transition (TF-S) to 400 °C for x = 0.2. The thermal expansion coefficient (αL) of the high-temperature scheelite phase was +11 ppm/°C, whereas for the low-temperature fergusonite phase, it was + 14 < αL < + 15 ppm/°C. The abrupt change in αL, the associated negative temperature coefficient of permittivity (τε), and the minimum value of εr at TF-S resulted in a near-zero TCF ∼ (+7.8 ppm/°C) for Nd(Nb0.8V0.2)O4 (εr ∼ 18.6 and Qf ∼ 70,100 GHz). A method to design near-zero TCF compositions based on modulation of τε and αL at TF-S is thus demonstrated that may also be extended to other fergusonite systems.

Multi-scale synergic optimization strategy for dielectric energy storage ceramics

Dielectric capacitors, serving as the indispensable components in advanced high-power energy storage devices, have attracted ever increasing attention with the rapid development of science and technology. Among various dielectric capacitors, ceramic capacitors with perovskite structure show unique advantages in actual application, such as excellent adaptability in high temperature environments. And the optimization of their energy storage performances has become a hot research topic recently. This review presents the basic principles of energy storage in dielectric ceramics and introduces multi-scale synergic optimization strategies according to the key factors for superior energy storage performance. By summarizing the common points in numerous works, several universal modification strategies are reviewed and future research on fatigue fracture of ceramic capacitors under multi-field including but not limited to force, electric and thermal coupling conditions is also anticipated.

Electrochemical properties of double molybdate LiSm(MoO4)2 ceramics with ultra-low sintering temperature

A novel double molybdate LiSm(MoO4)2 composition was prepared through a conventional solid-state ceramic route for its potential application as a solid-state Li+-ion conductor for low-loss dielectric ceramics. Ceramic disks were prepared by uniaxial pressing and sintered at the low temperature of 620 °C. Phase formation was confirmed through powder X-ray diffraction (XRD), which was indexed to the tetragonal crystal system with a Scheelite-type structure. Laser Raman spectroscopy showed that the MoO42− tetrahedra in the LiSm(MoO4)2 material are more regular, suggesting high symmetry for the compound. Scanning Electron Microscopy (SEM) revealed the formation of polygonal grains with an average grain size of less than 1 μm. The electrochemical properties of the ceramic system were investigated by Electrochemical Impedance Spectroscopy (EIS) in O2, air, and Ar (250 °C – 500 °C). Data were systematically analyzed using an Equivalent Circuit Model (EQM) combined with a Distribution Function of Relaxation Times (DFRT) analysis. The results revealed the coexistence of both a delocalized (long-range conductivity) and a localized (dipole relaxation) phenomenon, mainly distinguishable at lower temperatures (i.e., for T ≤ 350 °C) and in a pure O2 atmosphere. This localized phenomenon was tentatively attributed to the presence of trapped hole-vacancy pairs with reduced mobility. Conversely, at higher temperatures in O2 (i.e., for T ≥ 350 °C) and in the whole temperature range in less oxidizing conditions (air and Ar), such a localized phenomenon was no longer observed, as a likely result of a decrease in hole concentration with decreasing oxygen partial pressure (pO2). The current work, thus, underscores a different perspective for the development and characterization of ceramic-based solid-state Li+-ion conductors for their application as low-loss dielectric ceramics.

Enhanced optical transmittance and energy‐storage performance in NaNbO3‐modified Bi0.5Na0.5TiO3 ceramics

AbstractDielectric ceramics with both excellent energy storage and optical transmittance have attracted much attention in recent years. However, the transparent Pb‐free energy‐storage ceramics were rare reported. In this work, we prepared transparent relaxor ferroelectric ceramics (1 − x)Bi0.5Na0.5TiO3–xNaNbO3 (BNT–xNN) by conventional solid‐state reaction method. We find the NN‐doping can enhance the polarization and breakdown strength of BNT by suppressing the grain growth and restrained the reduction of Ti4+ to Ti3+. As a result, a high recoverable energy‐storage density of 5.14 J/cm3 and its energy efficiency of 79.65% are achieved in BNT–0.5NN ceramic at 286 kV/cm. Furthermore, NN‐doping can promote the densification to improve the optical transmittance of BNT, rising from ∼26% (x = 0.2) to ∼32% (x = 0.5) in the visible light region. These characteristics demonstrate the potential application of BNT–xNN as transparent energy‐storage dielectric ceramics.

Large permittivity, low loss and defect structure in (Nb, Zn) co-doped SnO2 ceramics studied through a combined experimental and DFT calculational method

Dielectric ceramics with high permittivity and low loss are widely used in electronic components and devices. In this study, (Nb, Zn) co-doped NbxZnySn1-x-yO2 with different doping levels and Nb/Zn ratios was designed to tune the defect structure toward the optimal dielectric performance. The lattice parameters firstly increased from x = y = 0.01 to 0.03 and then decreased, while the oxygen vacancy concentration decreased with doping. The co-doped sample with x = y = 0.02 exhibits stable permittivity up to 800 with an ultra-low loss tanδ ∼0.03 at 40 Hz. DFT calculation showed that the oxygen vacancy was formed with single-Zn doping and co-doping at low doping level, while the hole was generated at higher doping level. The achieved large permittivity and low loss of the sample are related to both Electron-Pinned Defect Dipoles (EPDD) and Hole-Pinned Defect Dipoles (HPDD) effects in the lattice, which was determined by the relative positions of donor and acceptor dopants.

Achieving high energy storage performance below 200 kV/cm in BaTiO3-based medium-entropy ceramics

A small applied electric field is particularly crucial in the practical application of dielectric ceramic capacitors, since it means a longer lifetime of the capacitors in practical energy storage applications. Based on the traditional ferroelectric BaTiO3, the (1-x)(Ba0.6Na0.2Bi0.2)TiO3-xNaNbO3 medium-entropy material is designed in this paper, which correlates configuration entropy with energy storage performance. The findings demonstrate that the BNBT-0.15NN ceramic synchronously achieves high energy storage density (2.95 J/cm3) and the energy storage efficiency (95.2%) at 180 kV/cm when the configuration entropy rises to 1.43R. The idea of medium-entropy energy storage under low electric field is proposed for the first time, opening up a new avenue for research into the preparation of high energy storage dielectric ceramics via exploring medium-entropy composition.

Synergistic modification of properties in Ba[(Zn0.8Mg0.2)1/3Nb2/3]O3 ceramics through ordered domain engineering

AbstractThe ordered domain engineering was investigated for Ba[(Zn0.8Mg0.2)1/3Nb2/3]O3 microwave dielectric ceramics to synergistically modify the physical properties especially the temperature coefficient of resonant frequency τf and quality factor Q value together with the thermal conductivity. The ordered domain structure could be tailored and controlled by the post‐densification annealing, and the fine ordered domain structures with high ordering degree and low‐energy domain boundary were obtained in the present ceramics annealed around 1400°C for 24 h, where the Qf value was improved from 51 000 to 118 000 GHz, τf was suppressed from 30 to 25.5 ppm/°C. Moreover, the thermal conductivity at room temperature was increased from 3.79 to 4.30 W m−1 K−1, and the Young's modulus was improved from 98 to 214 GPa. The present work provided a promising approach for synergistic modification of physical properties in Ba‐based complex perovskite microwave dielectric ceramics.