A Novel Magnetodielectric Solid Solution Ceramic 0.4LiFe5O8–0.6Li2MgTi3O8 with Excellent Microwave Dielectric Properties

In this study, a novel spinel solid solution ceramic of 0.4LiFe₅O₈–0.6Li₂MgTi₃O₈ (0.4LFO–0.6LMT) has been developed and investigated. It is found that the 40 mol% LiFe₅O₈ and 60 mol% Li₂MgTi₃O₈ are fully soluble in each other and a disordered spinel phase is formed. The ceramic sample sintered at 1050°C/2 h exhibits both good magnetic and dielectric properties in the frequency range 1–10 MHz, with a permeability between 29.9~14.1 and magnetic loss tangent between 0.12~0.67, permittivity between 16.92~16.94 and dielectric loss tangent between 5.9 × 10^?3–2.3 × 10^?2. The sample also has good microwave dielectric properties with a relative permittivity of 16.1, a high quality factor (Q × f) ~28 500 GHz (at 7.8 GHz). Furthermore, 3 wt% H₃BO₃–CuO (BCu) addition can effectively lower the sintering temperature to 925°C and does not degrade the magnetodielectric properties. The chemical compatibility with silver electrode indicates that this kind of ceramics is a good candidate for the low‐temperature cofired ceramic (LTCC) application.     

Dielectric Properties of Sol–Gel‐Derived Bi12SiO20 Thin Films

In this paper the dielectric properties of crack‐free, Bi₁₂SiO₂₀ thin films were investigated. The films were prepared on Pt/TiO₂/SiO₂/Si and corundum substrates using the sol–gel method. The formation of a pure Bi₁₂SiO₂₀ phase was observed at a temperature of 700°C. The Bi₁₂SiO₂₀ thin films, heat treated at 700°C for 1 h, had a dense microstructure with an average roughness (R_a) of 50 nm. The dielectric properties of the film were characterized by using both low‐ and microwave‐frequency measurement techniques. The low‐frequency measurements were conducted with a parallel capacitor configuration. The dielectric constant and dielectric losses were 44 and 7.5 × 10^?3, respectively. The thin‐film dielectric properties at the microwave frequency were measured using the split‐post, dielectric resonator method (15 GHz) and the planar capacitor configuration (1–5 GHz). The dielectric constant and the dielectric losses measured at 15 GHz were 40 and 17 × 10^?3, respectively, while the dielectric constant and the dielectric losses measured with the planar capacitor configuration were 39 and 65 × 10^?3, respectively.     

Ultra‐Low Fire Glass‐Free Li3FeMo3O12 Microwave Dielectric Ceramics

A new ultra‐low fire glass‐free microwave dielectric material Li₃FeMo₃O₁₂ was investigated for the first time. Single phase ceramics were obtained by the conventional solid‐state route after sintering at 540°C–600°C. The atomic packing fraction, FWHM of the A_g oxygen‐octahedron stretching Raman mode and Qf values of samples sintered at different temperatures correlated well with each other. The sample with a Lower Raman shift showed a higher dielectric constant. Interestingly, the system also showed a distinct adjustable temperature coefficient of resonant frequency (from ?84× 10^?6/°C to 25 × 10^?6/°C).     

Exceptionally High Dielectric Constant in Ceramic Pr2CuO4

The pristine layered cuprate Pr₂CuO₄ samples of >95% density were fabricated as thin disks. The samples, analyzed by X‐ray diffraction and Scanning electron microscopy, showed clean T′‐type phase with Rietveld refined lattice parameters a = b = 3.95805(±5) Å and c = 12.2262(±5) Å. The measured dielectric properties of the Pr₂CuO₄ ceramics, in the temperature range ?100°C–150°C and frequencies (ν) 0.1 Hz–1 MHz, showed extremely high ε_r′ > 10⁴ (above ?30°C), and dissipation (tan δ = ε_r′′/ε_r′) between 0.1 and 5 (for 500 Hz ≤ ν ≤ 1 MHz, and ?100 ≤ T ≤ 150°C). The ac conductivity of Pr₂CuO₄ ceramics ranged between 10^?6 and 10^?3 Scm^?1 for the measured frequencies and temperatures, and showed frequency‐dependent double power law behavior akin to a modified Jonscher's power law.     

A Novel Glass‐Ceramic with Ultra‐Low Sintering Temperature for LTCC Application

In this paper, the phase compositions and the dielectric properties of 3ZnO–2B₂O₃ glass‐ceramic prepared by solid‐state method were investigated. The X‐ray diffraction patterns show that all sintered samples consist of Zn₃B₂O₆ and α‐Zn(BO₂)₂. The dielectric properties changed significantly with the sintering temperature. After sintering at 650°C for 30 min, the glass‐ceramic exhibits optimum dielectric properties: a dielectric constant of 7.5 and a dielectric loss of 0.6 × 10^?3 at 10 MHz. The chemical compatibility with Ag electrode under the co‐fired process illustrates a potential application in low temperature co‐fired ceramic field for the glass‐ceramic.     

Microwave Dielectric Properties of Scheelite Structured PbMoO4 Ceramic with Ultralow Sintering Temperature

In this work, a low‐firing microwave dielectric ceramic PbMoO₄ with tetragonal structure was prepared via a solid‐state reaction method. The sintering temperature ranges from 570°C to 670°C. Ceramic samples with relative densities above 97% were obtained when sintering temperature was around 600°C. The best microwave dielectric properties were obtained in the ceramic sintered at 650°C for 2 h with a permittivity ~26.7, a Q × f value about 42 830 GHz (at 6.2 GHz) and a temperature coefficient value of 6.2 ppm/°C. From the X‐ray diffraction, backscattered electron imaging results of the cofired sample with 30 wt% silver and aluminum additive, the PbMoO₄ ceramic was found not to react with Ag and Al at 630°C. The microwave dielectric properties and low sintering temperature of PbMoO₄ ceramic make it a candidate for low‐temperature cofired ceramic applications.     

Microwave Dielectric Properties of Ultralow‐Temperature Cofirable Ba3V4O13 Ceramics

Ultralow‐temperature sinterable Ba₃V₄O₁₃ ceramics have been prepared through solid‐state ceramic route. Structural properties of the ceramic material are studied using powder X‐ray diffraction. Ba₃V₄O₁₃ ceramic has monoclinic structure and the existence of [V₄O₁₃]^6? polyhedra is confirmed through Laser Raman studies. The sample sintered at 600°C for 1 h shows dense microstructure with microwave dielectric properties of ε_r = 9.6, Q × f = 56 100 GHz, and τ_f = ?42 ppm/°C. The ceramics under study show good chemical compatibility with aluminum during cofiring.     

Facile Synthesis of “Quench‐Free Glass” and Ceramic‐Glass Composite for LTCC Applications

The 10 mol% ZnO–2 mol% B₂O₃–8 mol% P₂O₅–80 mol% TeO₂ (ZBPT) glass was prepared by quenching as well as slowly cooling the melt. The ZBPT glass prepared by both methods show similar microwave dielectric properties. ZBPT glass has an ε_r of 22.5 (at 7 GHz), Q_u × f of 1500 GHz, and τ_f of ?100 ppm/°C. The ceramic‐glass composites of Sr₂ZnTeO₆ (SZT) and ZBPT is prepared through two convenient methods: (a) conventional way of co‐firing the ceramic with ZBPT glass powder and (b) a nonconventional facile route by co‐firing the ceramic with precursor oxide mixture of ZBPT glass at 950°C. In the former route, SZT + 5 wt% ZBPT composite sintered at 950°C showed moderately good microwave dielectric properties (ε_r = 13.4, Q_u × f = 4500 GHz and τ_f = ?52 ppm/°C). Although the SZT + 5 wt% ZBPT composite prepared through the nonconventional method also showed similar microwave dielectric properties (ε_r = 13.8, Q_u × f = 5300 GHz and τ_f = ?50 ppm/°C), the synthesis procedure is much simplified in the latter case. The composites are found to be chemically compatible with Ag. The composite containing 5 wt% ZBPT prepared through conventional and nonconventional ways shows linear coefficients of thermal expansion of 7.0 ppm/°C and 7.1 ppm/°C, respectively. Both the composites have a room‐temperature thermal conductivity of 2.1 Wm^?1 K^?1.     

Phase Formation and Enhanced Dielectric Response of Y2/3Cu3Ti4O12 Ceramics Derived from the Sol–Gel Process

Y_2/3Cu₃Ti₄O₁₂ (YCTO) ceramics were successfully synthesized by sol–gel method (SG) and solid‐state method (SS), respectively. The optimized processing parameters for the syntheses of precursor powders by sol–gel process were determined as follows: the Ti(OC₄H₉)₄ concentration was 0.50 mol/L, the CH₃COOH volume was 8 mL, and the volume percentage of H₂O was 11.2%. Particularly, on the basis of XRD and TG‐DSC analyses, the phase formation temperature of YCTO‐SG was at least 100°C lower than that of YCTO‐SS. YCTO‐SG ceramics sintered at 1060°C for 25 h showed fine‐grained microstructure, and higher dielectric constant (ε′ ≈ 5.24 × 10⁴) at 1 kHz compared to YCTO‐SS ceramics (ε′ ≈ 0.93 × 10⁴). The higher dielectric constant of the YCTO‐SG ceramics was attributed to the grain size effect. Furthermore, the YCTO‐SG ceramics showed a distinct high‐temperature (>300°C) relaxor‐like behavior. According to the calculated activation energy value, the single ionization of oxygen vacancies was responsible for the conduction and dielectric anomaly behaviors of YCTO‐SG ceramics.     

Novel Low‐Firing Microwave Dielectric Ceramic LiCa3MgV3O12 with Low Dielectric Loss

Novel low temperature firing microwave dielectric ceramic LiCa₃MgV₃O₁₂ (LCMV) with garnet structure was fabricated by the conventional solid‐state reaction method. The phase purity, microstructure, and microwave dielectric properties were investigated. The densification temperature for the LCMV ceramic is 900°C. LCMV ceramic possessed ε_r = 10.5, Q_u × f = 74 700 GHz, and τ_f = ?61 ppm/°C. Furthermore, 0.90LiCa₃MgV₃O₁₂–0.10CaTiO₃ ceramic sintered at 925°C for 4 h exhibited good properties of ε_r = 12.4, Q_u × f = 57 600 GHz, and τ_f = 2.7 ppm/°C. The LCMV ceramic could be compatible with Ag electrode, which makes it a promising ceramic for LTCC technology application.     

Electrical Conductivity of Mullite Ceramics

The electrical conductivity of a lab‐produced homogeneous mullite ceramic sintered at 1625°C for 10 h with low porosity was measured by impedance spectroscopy in the 0.01 Hz to 1MHz frequency range at temperatures between 300°C and 1400°C in air. The electrical conductivity of the mullite ceramic is low at 300°C (≈0.5 × 10^?9 Scm^?1), typical for a ceramic insulator. Up to ≈ 800°C, the conductivity only slightly increases (≈0.5 × 10^?6 Scm^?1 at 800°C) corresponding to a relatively low activation energy (0.68eV) of the process. Above ≈ 800°C, the temperature‐dependent increase in the electrical conductivity is higher (≈10^?5 Scm^?1 at 1400°C), which goes along with a higher activation energy (1.14 eV). The electrical conductivity of the mullite ceramic and its temperature‐dependence are compared with prior studies. The conductivity of polycrystalline mullite is found to lie in‐between those of the strong insulator α‐alumina and the excellent ion conductor Y‐doped zirconia. The electrical conductivity of the mullite ceramic in the low‐temperature field (< ≈800°C) is approximately one order of magnitude higher than that of the mullite single crystals. This difference is essentially attributed to electronic grain‐boundary conductivity in the polycrystalline ceramic material. The electronic grain‐boundary conductivity may be triggered by defects at grain boundaries. At high temperatures, above ≈ 800°C, and up to 1400°C gradually increasing ionic oxygen conductivity dominates.     

Effect of Cobalt Doping on the Structural,Microstructure and Microwave Dielectric Properties of MgTiO3 Ceramics Prepared by Semi Alkoxide Precursor Method

We report a systematic investigation on crystal structure, microstructure, and microwave dielectric properties of (Mg_1?xCo_x)TiO₃ (x = 0–0.07) ceramics prepared by semialkoxide precursor method. All the as‐made samples exhibit an ilmenite structure with an incredible reduction in sintering temperature from 1350°C to 1200°C. Lattice parameter increases with increasing Co content due to the larger ionic radius of Co²⁺ as compared to Mg²⁺. The relative density, dielectric constant, and Q × f₀ values increase with increasing Co up to 0.05 and decreases for x > 0.05. This is attributed to local lattice distortion, maximum relative density, and uniform grain growth. Q × f₀ values were enhanced from 126 THz for x = 0 to a maximum value 170 THz for x = 0.05. A best combination of microwave dielectric properties (ε_r ~ 17.03, Q × f₀ ~ 170 THz @ 9.4 GHz and τ_f of ?40 ppm/°C) was obtained for (Mg_0.95Co_0.05)TiO₃ ceramic sintered at 1200°C for 3 h. The observed results reveal (Mg_0.95Co_0.05)TiO₃ ceramic as one of the promising dielectric materials for low‐loss and millimeter‐microwave applications.     

Structure and Dielectric Properties of Re0.02Sr0.97TiO3 (Re = La,Sm, Gd,Er) Ceramics for High‐Voltage Capacitor Applications

Rare–earth‐doped strontium titanate ceramics yielding the formula Re_0.02Sr_0.97TiO₃ (Re–ST, Re = La, Sm, Gd, Er) were prepared by solid‐state reaction route. All Re–ST ceramics had single cubic perovskite structure similar to pure SrTiO₃ (ST). The grain size of Re–ST ceramics dramatically decreased to 1–10 μm, depending on different rare‐earth elements, as compared to ~30 μm of pure ST. The relative dielectric constant of Re–ST ceramics (ε_r = 2750–4530 at 1 kHz) showed about 10–15 times higher than that of pure ST (ε_r = 300 at 1 kHz), whereas the dielectric loss of Re–ST ceramics still remained lower than 0.03 (at 1 kHz) at room temperature. Under 0–1.63 × 10⁶ V/m bias electric field testing conditions, the ε_r of Re–ST ceramics at room temperature changed within 14%. The P–E results indicated that the Re–ST ceramics were linear dielectrics. Together with their relatively high breakdown strength (E_b > 1.4 × 10⁷ V/m), the Re–ST ceramics could be very promising for high‐voltage capacitor applications. Meanwhile, the temperature stability of the ε_r of Re–ST ceramics was evaluated in a temperature range of ?60°C–200°C.     

High and temperature-stable dielectric constants in PNb9O25 ceramic

PNb₉O₂₅ ceramic was prepared using a sparking plasma sintering (SPS) method. Microstructure, dielectric and electrical properties of the ceramic were investigated. Dense ceramic was obtained, and the ceramic exhibited a high dielectric constant (>1000) and a low dielectric loss (∼2%) in the investigated frequency range of 100 Hz-100 kHz at room temperature. Dielectric relaxations with strong frequency dispersion occurred at temperatures higher than 250°C, which were due to oxygen vacancies. A highly stable capacitance (< 10% deviation) over a wide temperature range of –30°C to –200°C was obtained. The ceramic also showed a relatively high electrical conductivity (>4 × 10⁻⁸ S/cm) with an activation energy of approximately 0.9 eV in the temperature range of >200°C.     

Investigations on Material and Mechanical Properties,Air‐Permeation Behavior and Filtration Performance of Mullite‐Bonded Porous SiC Ceramics

A theoretical relation between processing parameters and porosity (29–56%) of mullite‐bonded porous SiC ceramics was derived and validated with experimental data. Porosity‐dependent variation of fracture strength (9–34 MPa) and elastic modulus (7–28 GPa) was explained by the minimum solid area model. At room temperature, the Darcian, k₁ (1.2 × 10^?13–1.6 × 10^?12 m²) and the non‐Darcian, k₂ (4.6 × 10^?9–2.7 × 10^?7 m) permeability coefficients showed linear variation with porosity. Tests conducted up to 650°C indicated an increase in k₁ with temperature and a reverse trend for k₂. Airborne NaCl nanoparticle filtration tests showed good performance of SiC ceramics with fractional collection efficiency of >99% at 46–56% porosity levels.     

Low‐Temperature Sinterable (1−x)Ba3(VO4)2–xLiMg0.9Zn0.1PO4 Microwave Dielectric Ceramics

The novel low‐temperature sinterable (1 ? x)Ba₃(VO₄)₂–xLiMg_0.9Zn_0.1PO₄ microwave dielectric ceramics were prepared by cofiring the mixtures of pure‐phase Ba₃(VO₄)₂ and LiMg_0.9Zn_0.1PO₄. The phase structure and grain morphology of the ceramics were evaluated using X‐ray diffraction, Raman spectra, and scanning electron microscopy. The results indicated that Ba₃(VO₄)₂ and LiMg_0.9Zn_0.1PO₄ phases can well coexist in the sintered body. Nevertheless, a small amount of LiZnPO₄ and some vanadate phases with low melting points were observed, which not only can influence the microwave dielectric properties of the ceramic but also can obviously improve the densification behavior at a relatively low sintering temperature. The near‐zero temperature coefficients of the resonant frequency (τ_f) could be achieved by adjusting the relative content of the two phases owing to their opposite τ_f values and simultaneously a desirable quality factor Q × f value can be maintained. No chemical reaction between the matrix ceramic phase and Ag took place after sintering at 800°C for 4 h. The ceramics with 45 vol% LiMg_0.9Zn_0.1PO₄ can be well sintered at only 800°C and exhibit excellent microwave dielectric properties of ε_r ~ 10, Q × f ~ 64 500 GHz, and τ_f ~ ?2.1 ppm/°C, thus showing a great potential as a low‐permittivity low‐temperature cofired microwave dielectric material.     

Microwave Dielectric Properties of LiKSm2(MoO4)4 Ceramics with Ultralow Sintering Temperatures

In this work, a novel low‐temperature firing microwave dielectric ceramic LiKSm₂(MoO₄)₄ was prepared via solid‐state reaction method. Ceramic samples with relative densities about 94.6% were obtained at sintering temperature 640°C–680°C. The best microwave dielectric properties was obtained in ceramic sample sintered at 620°C with a permittivity about 11.5, a Q × f value about 39 000 GHz and a temperature coefficient of frequency about ?15.9 ppm/°C. According to XRD patterns and backscattered electron micrograph, combined with Energy Dispersive Spectra analysis, of cofired samples with 30 wt% aluminum sintered at 620°C/4 h, the LiKSm₂(MoO₄)₄ ceramic was found to be chemically compatible with Al but react seriously with Ag, forming AgSmMo₂O₈ phase, at its sintering temperature.     

Enhanced pyroelectric properties in (Bi0.5Na0.5)TiO3–BiAlO3–NaNbO3 ternary system lead‐free ceramics

High pyroelectric performance and good thermal stability of pyroelectric materials are desirable for the application of infrared thermal detectors. In this work, enhanced pyroelectric properties were achieved in a new ternary (1?x)(0.98(Bi_0.5Na_0.5)(Ti_0.995Mn_0.005)O₃–0.02BiAlO₃)–xNaNbO₃ (BNT–BA–xNN) lead‐free ceramics. The effect of NN addition on the microstructure, phase transition, ferroelectric, and pyroelectric properties of BNT–BA–xNN ceramics were investigated. It was found that the average grain size decreased as x increased to 0.03, whereas increased with further NN addition. The pyroelectric coefficient p at room temperature (RT) was significantly increased from 3.87 × 10^?8Ccm^?2K^?1 at x = 0 to 8.45 × 10^?8Ccm^?2K^?1 at x = 0.03. The figures of merit (FOMs), F_i, F_v and F_d, were also enhanced with addition of NN. Because of high p (7.48 × 10^?8Ccm^?2K^?1) as well as relatively low dielectric permittivity (~370) and low dielectric loss (~0.011), the optimal FOMs at RT were obtained at x = 0.02 with F_i = 2.66 × 10^?10 m/V, F_v = 8.07 × 10^?2 m²/C, and F_d = 4.22 × 10^?5 Pa^?1/2, which are superior to other reported lead‐free ceramics. Furthermore, the compositions with x ≤ 0.03 exhibited excellent temperature stability in a wide temperature range from 20 to 80°C because of high depolarization temperature (≥110°C). Those results unveil the potential of BNT–BA–xNN ceramics for infrared detector applications.     

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.     

Dielectric properties of CaCu3Ti4O12 ceramics with Zn substitution for Cu

Abstract

CaCu_3–xZn_xTi₄O₁₂ (x is from 0 to 1·0) polycrystalline samples were fabricated via a two-step solid state reaction process. The lattice parameter of the monophasic CaCu₃Ti₄O₁₂ phase increased as Zn content increased. Scanning electron microscopy (SEM) images of the CCTO ceramic show bimodal grain size distribution and the grain size decrease largely with the appearance of Zn₂TiO₄ second phase. The dielectric permittivity of pure CCTO ceramic is ～1·5×10⁴ at f?=?100 Hz. The dielectric constant of the sample largely increased with Zn substitution in the frequency range f<10⁴ Hz. The highest dielectric constant was 6·2×10⁴ at f?=?100 Hz with Zn substitution of x?=?0·8. The improved dielectric properties are believed to be related to the presence of a thin grain boundary barrier layer. The resistivity of the grain boundary decreased largely with Zn substitution as evidenced from the impedance plots.