Effect of BaCu(B2O5) on the sintering temperature and microwave dielectric properties of BaO–Ln2O3–TiO2 (Ln = Sm,Nd) ceramics

BaCu(B₂O₅) (BCB) ceramic powder was used to decrease the sintering temperatures of BaSm₂Ti₄O₁₂ (BST) and BaNd₂Ti₅O₁₄ (BNT) ceramics. The sintering temperature of the BST and BNT ceramics was reduced from approximately 1350 °C to 850 °C by the addition of BCB. The bulk density of the specimens increased and reached the saturated value with increasing BCB content. The variation of the dielectric constant (ɛ_r) was similar to that of the bulk density and, thus, the relative density plays an important role in determining the ɛ_r value of the specimens. The Q-value initially increased with the addition of BCB but decreased considerably when a large amount of BCB was added because of the presence of the liquid phase. Good microwave dielectric properties of Qxf = 4500 GHz, ɛ_r = 60 and τ_f = −30 ppm/°C were obtained for the 16.0 mol% BCB-added BST ceramics sintered at 875 °C for 2 h.     

Effect of V2O5 additive to 0.4SrTiO3–0.6La(Mg0.5Ti0.5)O3 ceramics on sintering behavior and microwave dielectric properties

The effect of V₂O₅ addition on the microwave dielectric properties and the microstructures of 0.4SrTiO₃–0.6La(Mg_0.5Ti_0.5)O₃ ceramics sintered for 5 h at different sintering temperature were investigated systematically. It was found that the sintering temperature was effectively lowered about 200 °C by increasing V₂O₅ addition content. The grain sizes, bulk density as well as microwave dielectric properties were greatly dependent on sintering temperature and V₂O₅ content. The 4ST–6LMT ceramics with 0.25% V₂O₅ sintered at 1400 °C for 5 h in air exhibited optimum microwave dielectric properties of ɛ_r = 50.7, Q × f = 15049.6 GHz, T_f = −1.7 ppm/°C.     

Low-firing of BiSbO4 microwave dielectric ceramic with V2O5–CuO addition

Effects of 1.0 wt.% V₂O₅–CuO mixture addition on the sintering behavior, phase composition and microwave dielectric properties of BiSbO₄ ceramics have been investigated. BiSbO₄ ceramics can be well densified below temperature about 930 °C with 1.0 wt.% V₂O₅–CuO mixtures addition with different ratios of CuO to V₂O₅. The formation of BiVO₄ phase and substitution of Cu²⁺ can explain the decrease of sintering temperature. Dense BiSbO₄ ceramics sintered at 930 °C for 2 h exhibited good microwave dielectric properties with permittivity between 19 and 20.5, Qf values between 19,000 and 40,000 GHz and temperature coefficient of resonant frequency shifting between ?71.5 ppm °C^?1 and ?77.8 ppm °C^?1. BiSbO₄ ceramics could be a candidate for microwave application and low temperature co-fired ceramics technology.     

Preparation,phase structure and microwave dielectric properties of CoLi2/3Ti4/3O4 ceramic

A new low loss microwave dielectric ceramic with composition of CoLi_2/3Ti_4/3O₄ was prepared by a conventional solid-state reaction method. The compound has a cubic spinel structure [Fd-3m (227)] similar to MgFe₂O₄ with lattice parameters of a = 8.3939 Å, V = 591.42 Å³, Z = 8 and ρ = 4.30 g/cm³. This ceramic has a low sintering temperature (～1050 °C) and good microwave dielectric properties with relative permittivity of 21.4, Q × f value of 35,000 GHz and τ_f value of ?22 ppm/°C. Furthermore, the addition of BaCu(B₂O₅) (BCB) can effectively lower the sintering temperature from 1050 °C to 900 °C and does not induce much degradation of the microwave dielectric properties. Compatibility with Ag electrode indicates that the BCB added CoLi_2/3Ti_4/3O₄ ceramics are good candidates for LTCC applications.     

Synthesis of the giant dielectric constant oxide CaCu3Ti4O12 via ethylenediaminetetraacetic acid precursor

CaCu₃Ti₄O₁₂ powders were prepared via EDTA route and single-phase CaCu₃Ti₄O₁₂ was obtained at 800 °C for 2 h. DTA/TG and XRD were used to characterize the precursor and derived oxide powders. The dielectric properties of CaCu₃Ti₄O₁₂ ceramics were presented. Increasing sintering temperature leads to the increase in dielectric constant. CaCu₃Ti₄O₁₂ ceramics sintered at 1090 °C for 3 h exhibited giant dielectric constant of up to 2.1 × 10⁵ at room temperature and 100 Hz, which is significantly higher than those obtained from other chemical methods.     

Effect of B2O3 and CuO additives on the sintering temperature and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3 ceramics

B₂O₃ added Ba(Mg_1/3Nb_2/3)O₃ (BBMN) ceramics cannot be sintered below 930 °C. However, when CuO was added to them, they were sintered even at 850 °C. The amount of the Ba₂B₂O₅ second phase, which was formed in the BBMN ceramics decreased with the addition of CuO. Therefore, the CuO additive is considered to react with the B₂O₃ inhibiting the reaction between B₂O₃ and BaO. A dense microstructure without pores developed with the addition of a small amount of CuO. The bulk density, dielectric constant (ɛ_r) and Q-value increased with the addition of CuO, but decreased when a large amount of CuO was added. Excellent microwave dielectric properties were obtained for the Ba(Mg_1/3Nb_2/3)O₃ + 2.0 mol% B₂O₃ + 10.0 mol% CuO ceramic sintered at 875 °C for 2 h, with values Q_xf = 21 500 GHz, ɛ_r = 31 and temperature coefficient of resonance frequency (τ_f) = 21.3 ppm/°C.     

Microstructures and microwave dielectric properties of Ba4LiNb3O12–BaWO4 composite ceramics

Composite ceramics of (1 ? x)Ba₄LiNb₃O₁₂–xBaWO₄ (x = 0.36–0.69) had been synthesized by co-firing the mixtures of Ba₄LiNb₃O₁₂ and BaWO₄ powders. The structures and microwave dielectric properties of the ceramics were studied by XRD, SEM, and TEM. These ceramics consisted of hexagonal Ba₄LiNb₃O₁₂ and tetragonal BaWO₄. The two phases co-existed well in the ceramics, and there was not obvious reaction at interfacial areas among grains. These ceramics had low sintering temperatures and excellent microwave dielectric properties, especially the small temperature coefficients of resonant frequency (τ_f) and high quality factor (Q × f) values. For composition at x = 0.69, the ceramic sintered at 1070 °C had Q × f value of 75,500 GHz and τ_f value of +8.7 ppm/°C.     

Microwave dielectric properties of xNd(Zn1/2Ti1/2)O3–(1 − x)CaTiO3 ceramics

The microwave dielectric properties of xNd(Zn_1/2Ti_1/2)O₃–(1 − x)CaTiO₃ have been investigated. The system has been prepared by a conventional solid state ceramic route. Nd(Zn_1/2Ti_1/2)O₃ (NZT) possesses a dielectric constant (ε_r) of 32, a high quality factor (Q × f) of 170,000 GHz and a temperature coefficient of resonant frequency (τ_f) of − 42 ppm/°C. In order to produce a temperature-stable material, the addition of CaTiO₃ leads to a near-zero temperature variation of resonant frequency. In general, the microwave quality factor (Q × f) decreased as x increased and the temperature coefficient of resonant frequency (τ_f) was approximately linearly proportional to permittivity. The dielectric constant decreases from 77 to 32 as x varies from 0.2 to 1.0. The dielectric constant (ε_r) of 45, Q × f value of 56,000 (at 6 GHz) and temperature coefficient of resonant frequency (τ_f) of 0 ppm/°C were obtained for 0.5Nd(Zn_1/2Ti_1/2)O₃–0.5CaTiO₃ ceramics sintered at 1300 °C for 4 h. As the content of x increases, the highest Q × f value of 136,200 GHz for x = 0.8 is achieved at the sintering temperature 1300 °C.     

Low-temperature sintering and microwave dielectric properties of CaTi1−x(Fe0.5Nb0.5)xO3 ceramics with B2O3 addition

CaTi_1−x(Fe_0.5Nb_0.5)_xO₃ (0 ≤ x ≤ 1) dielectrics were synthesized via the solid state reaction route and structure analysis was performed together with the dielectric characterization. The substitution of Ti⁴⁺ by Fe³⁺/Nb⁵⁺ and developed phase were studied by X-ray diffraction. The dielectric constant and temperature coefficient of resonant frequency decrease rapidly with an increase of x. The influence of 1–5 wt.% B₂O₃ as a sintering additive investigated at CaTi_0.5(Fe_0.5Nb_0.5)_0.5O₃ solid solutions. The dielectric properties were found to strongly depend on the sintering conditions and contents of B₂O₃ additions. ɛ_r = 52.3, Q × f_o = 2930 GHz and T_f = 13 ppm/°C were obtained for CaTi_0.5(Fe_0.5Nb_0.5)_0.5O₃ specimen 3 wt.% B₂O₃ sintered at 900 °C for 2 h.     

Influence of V2O5 additions to Ba(Mg1/3Ta2/3)O3 ceramics on sintering behavior and microwave dielectric properties

The microstructures and the microwave dielectric properties of barium magnesium tantalate ceramics prepared by conventional mixed oxide route have been investigated. The prepared Ba(Mg_1/3Ta_2/3)O₃ exhibited a mixture of cubic perovskite and a hexagonal superstructure with Mg and Ta showing 1:2 order in the B-site. It is found that low level doping of V₂O₅ (up to 0.5 wt.%) can significantly improve densification of the specimens and their microwave dielectric properties. The density of doped Ba(Mg_1/3Ta_2/3)O₃ ceramics can be increased beyond 95% of its theoretical value by 1500 °C-sintering, which is caused by the liquid-phase effect of V₂O₅ addition. The detected second phase Ta₂O₅ was mainly the result of V⁵⁺ substitution in the ceramics. Dielectric constant (ε_r) and temperature coefficient of resonant frequency (τ_f) were not significantly affected, while the unloaded quality factors Q were effectively promoted by V₂O₅ addition due to the increase in B-site ordering. The ε_r value of 24.1, Q×f value of 149,000 (at 10 GHz) and τ_f value of 7.2 ppm/°C were obtained for Ba(Mg_1/3Ta_2/3)O₃ ceramics with 0.25 wt.% V₂O₅ addition sintered at 1500 °C for 3 h.     

Effects of CaF2 addition on sintering behavior and microwave dielectric properties of ZnTa2O6 ceramics

Microwave dielectric ceramics ZnTa₂O₆ were prepared by conventional mixed oxide route. The effects of CaF₂ addition on the microstructures and microwave dielectric properties of ZnTa₂O₆ ceramics were investigated. Formation of second phase can be detected at the high addition of CaF₂ (0.5–1.0 wt.%). Variation of grain shapes were observed with CaF₂ content increasing. The sintering temperature of CaF₂-doped ZnTa₂O₆ ceramics can be effectively lowered from 1400 °C to 1225 °C due to liquid phase effect. The microwave dielectric properties were affected by the amount of CaF₂ addition. At 1225 °C for 4 h, ZnTa₂O₆ ceramics with 0.25 wt.% CaF₂ possesses excellent microwave dielectric properties: ε_r = 31.32, Q × ? = 73600 GHz(6.8 GHz) and τ_? = ? 6.97 ppm/°C.     

Low-temperature firing and microwave dielectric properties of MgTiO3 ceramics with Bi2O3–V2O5

The effects of Bi₂O₃–V₂O₅ additive on the microstructures, the phase formation and the microwave dielectric properties of MgTiO₃ Ceramics were investigated. The Bi₂O₃–V₂O₅ addition lowered the sintering temperature of MgTiO₃ ceramics effectively from 1400 to 875 °C due to the liquid-phase effect. The microwave dielectric properties were found to strongly correlate with the amount of Bi₂O₃–V₂O₅ addition. The saturated dielectric constant decreased and the maximum Qf values increased with the increasing V₂O₅ content, which is attributed to the variation of the second phase including Bi₂Ti₂O₇, Bi₄V_1.5Ti_0.5O_10.85 and BiVO₄. At 875 °C, MgTiO₃ ceramics with 5.0 mol% Bi₂O₃–7 mol% V₂O₅ gave excellent microwave dielectric properties: ε_r = 20.6,Qf = 10420 GHz (6.3 GHz).     

Enhanced densification and microwave dielectric properties of Mg2TiO4 ceramics added with CeO2 nanoparticles

We report the study of the effects of processing parameters and additive concentration on the structure, microstructure and microwave dielectric properties of MTO–CeO₂ (x wt.%) ceramics with x = 0, 0.5, 1.0 and 1.5 prepared by solid-state reaction method by adding CeO₂ nanoparticles as a sintering aid. The pure Mg₂TiO₄ ceramics were not densifiable below 1450 °C. However, when CeO₂ nanoparticles were added to MTO, the densification achieved at 1300 °C along with the increase in average grain size with the uniform microstructure and improved microwave dielectric properties. This is mainly driven by the large surface energy of CeO₂ nanoparticles and their defect energy during the sintering process. While the addition of CeO₂ nanoparticles in MTO ceramics does not change the dielectric constant (?_r), the unloaded quality factor (Q_u) was altered significantly. MTO–CeO₂ (1.5 wt.%) ceramics sintered at 1300 °C exhibit superior microwave dielectric properties (?_r ～ 14.6, Q × f₀ ～ 167 THz), as compared to the pure Mg₂TiO₄ ceramics. The observed results are correlated to the enhancement in density and the development of uniform microstructure with the enhanced grain size.     

Low temperature sintering and microwave dielectric properties of Ba4Sm9.33Ti18O54 ceramics

The effect of BaCu(B₂O₅) (BCB) on the sinterability, microstructure and microwave dielectric properties of Ba₄Sm_9.33Ti₁₈O₅₄ (BST) has been investigated. Dilatometric measurements reveal that the sintering temperature of BST can be reduced by the addition of BCB. Microstructural analysis shows abnormal grain growth with large amount of BCB. A ceramic composite with Q × f = 4000 GHz, ?_r = 52 and τ_f = ?29 ppm/°C which can be sintered at 950 °C is obtained when 10 wt% BCB is added to BST. EDS analysis shows that the composite is chemically compatible with silver.     

Modified giant dielectric properties of samarium doped CaCu3Ti4O12 ceramics

Effects of Sm³⁺ substitution on the microstructure and dielectric properties of CaCu₃Ti₄O₁₂ ceramics were investigated. The grain size of CaCu₃Ti₄O₁₂ ceramics was greatly decreased by doping with Sm³⁺, resulting from the ability of Sm³⁺ to inhibit the grain growth rate. This result can cause a decrease in the dielectric constant (?′) and loss tangent (tan δ) of CaCu₃Ti₄O₁₂ ceramics. Interestingly, high dielectric permittivity (?′ ～ 10,863) and low loss tangent (tan δ ～ 0.043 at 20 °C and 1 kHz) were observed in the Ca_0.925Sm_0.05Cu₃Ti₄O₁₂ ceramic. Nonlinear electrical properties of CaCu₃Ti₄O₁₂ ceramics were modified by doping with Sm³⁺. The dielectric relaxation behavior of Sm-doped CaCu₃Ti₄O₁₂ ceramics can be well ascribed based on the internal barrier layer capacitor model of Schottky barriers at the grain boundaries.     

Structure and microwave dielectric characteristics of lithium-excess Ca0.6Nd0.8/3TiO3/(Li0.5Nd0.5)TiO3 ceramics

Compositions based on (1−x)Ca_0.6Nd_8/3TiO₃−x(Li_1/2Nd_1/2)TiO₃ + yLi (CNLNTx + yLi, x = 0.30–0.60, y = 0–0.05), suitable for microwave applications have been developed by systematically adding excess lithium in order to tune the microwave dielectric properties and lower sintering temperature. Addition of 0.03 excess-Li simultaneously reduced the sintering temperature and improved the relative density of sintered CNLNTx ceramics. The excess Li addition can compensate the evaporation of Li during sintering process and decrease the secondary phase content. The CNLNTx (x = 0.45) ceramics with 0.03 Li excess sintered at 1190 °C have single phase orthorhombic perovskite structure, together with the optimum combination of microwave dielectric properties of ɛ_r = 129, Q × f = 3600 GHz, τ_f = 38 ppm/°C. Obviously, excess-Li addition can efficiently decrease the sintering temperature and improve the microwave dielectric properties. The high permittivity and relatively low sintering temperatures of lithium-excess Ca_0.6Nd_0.8/3TiO₃/(Li_0.5Nd_0.5)TiO₃ ceramics are ideal for the development of low cost ultra-small dielectric loaded antenna.     

Preparation of a–b plane oriented Nb-doped Bi4Ti3O12 ceramics by magnetic alignment via gelcasting

Highly a–b plane grain-oriented Nb-doped Bi₄Ti₃O₁₂ ceramics (Bi₄Ti_2.96Nb_0.04O₁₂, BINT) were successfully prepared by magnetic alignment (MA) via gelcasting technique using only conventional solid-state-synthesized starting powder. The micro-size BINT particles with irregular shape were aligned in slurry by strong magnetic force and then in situ locked by polymerization via gelcasting technique in 30 min in a 10 T magnetic field. Highly a–b plane orientation parallel to the magnetic field direction (//B) was obviously observed in the green compact (f_(200)/(020) = 0.41) and sintered sample (f_(200)/(020) = 0.67). The sintered sample contained plate-like grains and reached 97% theoretical density. Compared to the controlled sample without magnetic alignment, the magnetically aligned sample shows enhanced dielectric constant in //B direction (160 versus 120 at room temperature and 350 versus 250 at 580 °C). This method, using typical gelcasting technique in a strong magnetic field, readily applicable to prepare other ceramics and is expected to facilitate the mass preparation of large and dense grain-oriented ceramic components.     

Microwave dielectric properties of Ba3La2Ti2Nb2−xTaxO15 ceramics

High dielectric constant and low loss ceramics in the system Ba₃La₂Ti₂Nb_2−xTa_xO₁₅ (x = 0–2) have been prepared by conventional solid-state ceramic route. Ba₃La₂Ti₂Nb_2−xTa_xO₁₅ solid solutions adopted A₅B₄O₁₅ cation-deficient hexagonal perovskite structure for all compositions. The materials were characterized at microwave frequencies. They show a linear variation of dielectric properties with the value of x. Their dielectric constant varies from 49.8 to 45.1, quality factor Q_u × f from 22,000 to 31,040 GHz and temperature variation of resonant frequency from + 6.9 to − 13.4 ppm/°C as the value of x increases. These low loss ceramics might be used for dielectric resonator (DR) applications.     

Microwave dielectric properties of BaO–TeO2 binary compounds

A series of BaO–TeO₂ binary ceramic compounds were explored for microwave dielectric applications with ultra-low processing temperatures. During the calcination of mixed BaCO₃ and TeO₂ raw powders, BaTe₄O₉, BaTe₂O₆, BaTeO₃, and Ba₂TeO₅ phases were obtained through the sequential phase formations from Te-rich to Ba-rich phases at temperatures ranging from 500 to 850 °C. Sintering temperatures were as low as only 550 °C for the Te-rich phases. Barium tellurate ceramics exhibited excellent microwave dielectric properties with intermediate dielectric permittivities and high quality factors (Q). The dielectric properties at microwave frequencies were ε_r = 10–21, Q × f = 34,000–55,000 GHz, and TCf = − 51 to − 124 ppm/°C, depending on compositions.     

Preparation and dielectric properties of Sr(Ti0.95Zr0.05)O3 ceramics doped with CaOTiO2SiO2 (CTS)

Sr(Ti_0.95Zr_0.05)O₃ ceramic was sintered using x mol.% CTS (x = 0, 0.5, 1.5, 4, 7) as sintering additive for the first time. Although Sr(Ti_0.95Zr_0.05)O₃ ceramic could not be fully sintered even at 1420 °C, the densification temperature could be decreased to 1280 °C by using CTS, which begin melting when temperature reaches higher than 1150 °C. The microstructures of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). Apparent density and the dielectric properties were established at room temperature. The measuring frequency was 1 MHz. The microstructure and dielectric properties greatly changed depending on the amount of CTS additive. The optimum concentration to obtain nicer dielectric properties was 0.5 mol.%.