Microwave dielectric properties and low-temperature sintering of Ba3Ti4Nb4O21 ceramics with B2O3 and CuO additions

The low sintering temperature and the good dielectric properties such as high dielectric constant (ɛ_r), high quality factor (Q × f) and small temperature coefficient of resonant frequency (τ_f) are required for the application of chip passive components in the wireless communication technologies. In the present study, the sintering behaviors and dielectric properties of Ba₃Ti₄Nb₄O₂₁ ceramics were investigated as a function of B₂O₃–CuO content. Ba₃Ti₄Nb₄O₂₁ ceramics with B₂O₃ or CuO addition could be sintered above 1100 °C. However, the additions of both B₂O₃ and CuO successfully reduced the sintering temperature of Ba₃Ti₄Nb₄O₂₁ ceramics from 1350 to 900 °C without detriment to the microwave dielectric properties. From the X-ray diffraction (XRD) studies, the sintering behaviors and the microwave dielectric properties of low-fired Ba₃Ti₄Nb₄O₂₁ ceramics were examined and discussed in the formation of the secondary phases. The Ba₃Ti₄Nb₄O₂₁ sample with 1 wt% B₂O₃ and 3 wt% CuO addition, sintered at 900 °C for 2 h, had the good dielectric properties: ɛ_r = 65, Q × f = 16,000 GHz and τ_f = 101 ppm/°C.     

Influence of Ti4+ substitution for Ta5+ on the crystal structure,Raman spectra,and microwave dielectric properties of Ba3Ta4-4xTi4+5xO21 ceramics

This paper systematically investigated the influence of Ti⁴⁺ substitution for Ta⁵⁺ on the phase composition and microwave dielectric properties of Ba₃Ta_4-4xTi_4+5xO₂₁ (x = 0.1, 0.2, and 0.3) ceramics with hexagonal tungsten bronze-like structures. X-ray diffraction and Rietveld refinement results indicated that single-phase Ba₃Ta₄Ti₄O₂₁ could be obtained only with the x values of 0.1 and 0.2, and a secondary phase was detected at an x value of 0.3. The valence state of Ba₃Ta_4-4xTi_4+5xO₂₁ (x = 0.2) ceramics was analyzed through X-ray photoelectron spectroscopy. Increasing Ti⁴⁺/Ta⁵⁺ ratios could reduce sintering temperature and improve the microwave dielectric properties of Ba₃Ta_4-4xTi_4+5xO₂₁ solid solutions. However, the dielectric properties, particularly the quality factor, of Ba₃Ta_4-4xTi_4+5xO₂₁ ceramics deteriorated severely as a result of oxygen vacancy defects caused by the transition of the valence state from Ti⁴⁺ to Ti³⁺ when x = 0.2 and the coexistence of the secondary phase when x = 0.3. Infrared reflectivity spectroscopy was performed to explore the intrinsic dielectric properties of Ba₃Ta_4-4xTi_4+5xO₂₁ (x = 0.1) ceramics. The measured and extrapolated microwave dielectric properties of Ba₃Ta_4-4xTi_4+5xO₂₁ (x = 0.1) ceramics sintered at 1240 °C for 6 h were ε_r ~ 46.5, Q × f = 13,900 GHz, τ_f ~ +49.4 ppm/°C, and ε_r ~ 44, Q × f = 34,850 GHz.     

Low‐Temperature Sintering Microwave Characteristics of B2O3‐doped CaLa4Ti4O15 Dielectric Ceramics

Preparation and microwave dielectric properties of B₂O₃‐doped CaLa₄Ti₄O₁₅ ceramics have been investigated. X‐ray diffraction data show that CaLa₄Ti₄O₁₅ ceramic has a trigonal structure coupled with a second phase of CaLa₄Ti₅O₁₇. The CaLa₄Ti₄O₁₅ ceramic with addition of 0.5 wt% B₂O₃, sintered at 1220°C for 4 h, exhibits microwave dielectric properties with a dielectric constant of 45.8, Q × f value of 24,000 GHz, and temperature coefficient of resonant frequency (τ_f) of ?19 ppm/^°C. B₂O₃‐doped CaLa₄Ti₄O₁₅ ceramics, which have better sintering behavior (decrease in sintering temperature ~ 330°C) and dielectric properties than pure CaLa₄Ti₄O₁₅ ceramics, are candidates for applications in microwave devices.     

Enhanced dielectric,ferroelectric and magnetic properties of Ba4Sm2Fe2Nb8O30 RT multiferroics prepared by microwave sintering

High density Ba₄Sm₂Fe₂Nb₈O₃₀ (BSFN) multiferroics ceramics with tetragonal tungsten bronze structure had been prepared by microwave sintering (MS) for 30min and conventional sintering (CS) methods for 4 h at 1275 °C. Single tungsten bronze phase and equiaxial grains are obtained for the MS BSFN ceramics, while a small amount secondary phase of SmNbO₄ is observed in the CS BSFN ceramics with columnar grains. Compared to Ba₄Sm₂Fe₂Nb₈O₃₀ ceramics prepared by CS method, enhanced dielectric, ferroelectric and magnetic properties are achieved for the MS BSFN ceramics. The values of electric polarization Pr and coercive electric field Ec are 2.11 μC/cm² and 7.14 kV/cm for the MS BSFN ceramics, respectively. Meantime, the magnetic polarization Mr of 0.410emu/g and coercive magnetic field Hc of 2930Oe are also obtained for the MS BSFN ceramics. Based on the density, crystal structure, point defect and grain, the reasons of enhanced dielectric, ferroelectric and magnetic properties are discussed for the MS BSFN ceramics It is indicated that Ba₄Sm₂Fe₂Nb₈O₃₀ is an intrinsic room temperature multiferroic materials.     

Crystal structural and microwave dielectric properties of Ba4B'Nb3O12 (B′=Yb,Tm, Er,Y, Ho,Dy, Gd) ceramics

The influence of substitution of rare-earth ion (RE = Yb, Tm, Er, Y, Ho, Dy, Gd) for B′-site on phase composition, crystal structure, micromorphology, and microwave dielectric properties of Ba₄RENb₃O₁₂ ceramics are investigated. The results of XRD and Rietveld refinement indicate that the Ba₄RENb₃O₁₂ ceramic is composed of Ba(RE_1/12Nb_9/12)O₃ and Ba (RE_1/2Nb_1/2)O₃ phases. Porosity analysis shows that the relative density of Ba₄RENb₃O₁₂ ceramics can reach more than 95.25%. The variations of permittivity and temperature coefficient are associated with ionic polarization and cell polarization, respectively. The A_1g Raman‐active modes at 754 cm^?1 are oxygen-octahedron stretch vibration, reflecting the variation of the structure. Optimal microwave dielectric properties (ε_r = 38.75, Q × f = 41251 GHz, τ_f = 71.57 ppm/°C) of Ba₄RENb₃O₁₂ ceramics for RE = Yb are obtained at 1425 °C for 6 h.     

BaO–TiO2 microwave ceramics

In this paper, the structure and dielectric properties of BaO–TiO₂ system ceramics were studied. By adding ZnO and Nb₂O₅ as sintering agents to the raw materials, the BaO–TiO₂ system ceramics were sintered at a temperature of 1260 °C for 2 h and have superior dielectric properties at 1 GHz: quality factor Q=12,500, relative dielectric constant ε_r≈37, temperature coefficient of dielectric constant α_ε=0±30 ppm/°C. XRD pattern shows that the main crystal phase of the ceramics is Ba₂Ti₉O₂₀, accompanied by a small number of additional phases: BaTi₄O₉, Ba₄Ti₁₃Zn₇O₃₄, Ba₄Ti₁₃O₃₀ and Ti₂Nb₁₀O₂₉, etc. The initial Ba/Ti ratio has a great effect on the dielectric properties of the ceramics, which can be explained by the variance in the formation of phases due to different Ba/Ti ratios.     

Structure,Microwave Dielectric Properties and Thermally Stimulated Depolarization Currents of (1 − x)Ba0.6Sr0.4La4Ti4O15–xBa5Nb4O15 Solid Solutions

(1 ? x)Ba_0.6Sr_0.4La₄Ti₄O₁₅–xBa₅Nb₄O₁₅ (x = 0.05, 0.1, 0.15 and 0.2, BSLT–BN) ceramic samples were prepared by co‐firing the mixtures of Ba_0.6Sr_0.4La₄Ti₄O₁₅ and Ba₅Nb₄O₁₅ powders. Crystal structure, microwave dielectric properties and thermally stimulated depolarization currents (TSDC) of the BSLT–BN series ceramics were investigated. X‐ray diffraction patterns reveal that all the samples exhibit a hexagonal perovskite structure, which implies that the BSLT–BN mixtures form solid solutions. With increasing Ba₅Nb₄O₁₅ content, the diffraction peaks shift to low angles and the sintering temperature of BSLT–BN decreases. Raman spectra analysis reveals the shifting and splitting of the vibration modes. The microwave dielectric properties of the well‐sintered (1 ? x)BSLT–xBN ceramics vary with Ba₅Nb₄O₁₅ content. The dielectric permittivity of the ceramics exhibits a slight decreasing trend. The quality factor varies in the range of 45 000–11 200 GHz, whereas near‐zero temperature coefficients of the resonant frequency may be achieved by changing the Ba₅Nb₄O₁₅ content. TSDC was utilized to explore the extrinsic loss mechanism associated with defects. TSDC relaxation peaks are mainly generated by oxygen vacancies, and the Ba₅Nb₄O₁₅ content has a significant influence on the TSDC spectra.     

Low temperature sintering and microwave dielectric properties of Ba3Ti5Nb6O28 with ZnO–B2O3 glass additions for LTCC applications

The effects of ZnB₂O₄ glass additions on the sintering temperature and microwave dielectric properties of Ba₃Ti₅Nb₆O₂₈ have been investigated using dilatometer, X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and a network analyzer. The pure Ba₃Ti₅Nb₆O₂₈ system showed a high sintering temperature (1250 °C) and had the good microwave dielectric properties: Q × f of 10,600 GHz, ɛ_r of 37.0, τ_f of −12 ppm/°C. It was found that the addition of ZnB₂O₄ glass to Ba₃Ti₅Nb₆O₂₈ lowered the sintering temperature from 1250 to 925 °C. The reduced sintering temperature was attributed to the formation of ZnB₂O₄ liquid phase and B₂O₃-rich liquid phases. Also the addition of ZnB₂O₄ glass enhanced the microwave dielectric properties: Q × f of 19,100 GHz, ɛ_r of 36.6, τ_f of 5 ppm/°C. From XPS and XRD studies, these phenomena were explained in terms of the reduction of oxygen vacancies and the formation of secondary phases having the good microwave dielectric properties.     

Microwave dielectric properties of Ba3Ti4−x(Zn1/3Nb2/3)xNb4O21 for low temperature co-fired ceramics

The effects of substitution of (Zn_1/3Nb_2/3) for Ti on the sintering behavior and microwave dielectric properties of Ba₃Ti_4−x(Zn_1/3Nb_2/3)_xNb₄O₂₁ (0 ≤ x ≤ 4) ceramics have been investigated. The dielectric constant (?_r) and the temperature coefficient of the resonant frequency (τ_f) of Ba₃Ti_4−x(Zn_1/3Nb_2/3)_xNb₄O₂₁ ceramics decreased with increasing x. However, the Q × f values enhanced with the substitution of (Zn_1/3Nb_2/3) for Ti. It was found that a small amount of MnCO₃-CuO (MC) and ZnO-B₂O₃-SiO₂ (ZBS) glass additives to Ba₃Ti_4−x(Zn_1/3Nb_2/3)_xNb₄O₂₁ (x = 2) ceramics lowered the sintering temperature from 1250 to 900 °C. And Ba₃Ti_4−x(Zn_1/3Nb_2/3)_xNb₄O₂₁ (x = 2) ceramics with 1 wt% MC and 1 wt% ZBS sintered at 900 °C for 2 h showed excellent dielectric properties: ?_r = 53, Q × f = 14,600 GHz, τ_f = 6 ppm/°C. Moreover, it has a chemical compatibility with silver, which made it as a promising material for low temperature co-fired ceramics technology application.     

Good thermal stability,giant permittivity,and low dielectric loss for X9R-type (Ag1/4Nb3/4)0.005Ti0.995O2 ceramics

With the intense demand of the developing microelectronics market, the study of giant permittivity dielectric materials is being promoted. However, it is difficult to obtain suitable dielectric materials for such applications, especially due to high dielectric loss at low frequencies. In this work, Ag+Nb codoped TiO₂ ceramics were designed and fabricated in a conventional solid reaction by sintering at 1290-1340°C for 5-10 hours. The issue of how the microstructure and dielectric properties of (Ag_1/4Nb_3/4)_0.005Ti_0.995O₂ ceramics are affected by the sintering conditions was discussed. By optimizing sintering conditions, a dense microstructure, a high dielectric constant (ε_r ≈ 9410), and a low dielectric loss (tanδ ≈ 0.037) at 1 kHz were achieved. Most importantly, the temperature coefficient value of ε_r at different frequencies remained stable between −14.3% and 13.7% within the temperature range from −190 to 200°C, which has potential applications in X9R capacitor.     

Structural dependence of microwave dielectric properties in ilmenite-type Mg(Ti1-xNbx)O3 solid solutions by Rietveld refinement and Raman spectra

Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics were prepared by the conventional solid-state reaction method. The phase composition, sintering characteristics, microstructure and dielectric properties of Ti⁴⁺ replacement by Nb⁵⁺ in the formed solid solution Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics were systematically studied. The structural variations and influence of Nb⁵⁺ doping in Mg(Ti_1-xNb_x)O₃ were also systematically investigated by X-ray diffraction and Raman spectroscopy, respectively. X-ray diffraction and its Rietveld refinement results confirmed that Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics crystallised into an ilmenite-type with R-3 (148) space group. The replacement of the low valence Ti⁴⁺ by the high valence Nb⁵⁺ can improve the dielectric properties of Mg(Ti_1-xNb_x)O₃ (x = 0–0.09). This paper also studied the different sintering temperatures for Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics. The obtained results proved that 1350 °C is the best sintering temperature. The permittivity and Q × f initially increased and then decreased mainly due to the effects of porosity caused by the sintering temperature and the doping amount of Nb₂O₅, respectively. Furthermore, the increased Q × f is correlated to the increase in Ti–O bond strength as confirmed by Raman spectroscopy, and the electrons generated by the oxygen vacancies will be compensated by Nb⁵⁺ to a certain extent to suppress Ti⁴⁺ to Ti³⁺, which was confirmed by XPS. The increase in τ_f from ?47 ppm/°C to ?40.1 ppm/°C is due to the increment in cell polarisability. Another reason for the increased τ_f is the reduction in the distortion degree of the [TiO₆] octahedral, which was also confirmed by Raman spectroscopy. Mg(Ti_0.95Nb_0.05)O₃ ceramics sintered at 1350 °C for 2 h possessed excellent microwave dielectric properties of ε_r = 18.12, Q × f = 163618 GHz and τ_f = ?40.1 ppm/°C.     

Low-temperature sintering and microwave dielectric properties of Ba5Nb4O15 with ZnB2O4 glass

The Influence of ZnB₂O₄ glass addition on the sintering temperature and microwave dielectric properties of Ba₅Nb₄O₁₅ has been investigated using dilatometry, X-ray diffraction, scanning electron microscopy and network analyzer. It was found that a small amount of glass addition to Ba₅Nb₄O₁₅ lowered the sintering temperature from 1400 to 900 °C. The reduced sintering temperature was attributed to the formation of ZnB₂O₄ liquid phase and B₂O₃-rich liquid phases such as Ba₃B₂O₆. The Ba₅Nb₄O₁₅ ceramics with ZnB₂O₄ glass, sintered at a low temperature, exhibited good microwave dielectric characteristics, i.e., a quality factor (Q × f) = 12,100 GHz, a relative dielectric constant (ɛ_r) = 40, a temperature coefficient of resonant frequency (τ_f) = 48 ppm/°C. The dielectric properties were discussed in terms of the densification of specimens and the influence of glassy phases such as Ba₃B₂O₆ and ZnB₂O₄.     

Structure and electrical properties evolution of B-site complex ions (Li1/4Nb3/4) modification BNT–BT ceramics

Abstract

B-site complex ions (Li_1/4Nb_3/4)⁴⁺ modification (Bi_1/2Na_1/2)_0·94Ba_0·06TiO₃ ceramics with compositions of (Bi_1/2Na_1/2)_0·94Ba_0·06Ti_1?x(Li_1/4Nb_3/4)_xO₃ (x?=?0, 0·01, 0·03 and 0·06) have been synthesised via the conventional solid state reaction. The effect of (Li_1/4Nb_3/4)⁴⁺ content and sintering temperature on structures and electrical properties were investigated. It was found that both compositions and sintering temperatures have no significant effect on the crystal structure, and trace (Li_1/4Nb_3/4)⁴⁺ addition and sintering temperatures have a great influence on the microstructure. Two obvious dielectric anomaly peaks (T_d and T_m) were observed and dielectric constant for all poled specimens displayed significant frequency dispersion at T_d and diffusion phase transition at T_m. The piezoelectric properties of the ceramics are insensitive to the sintering temperatures, and the composition with x?=?0·03 sintering at 1150°C exhibits favourable piezoelectric properties of d₃₃?=?155 pC N^?1 and k_p?=?0·312.     

Improvement of microwave dielectric properties of the LiNb0.6Ti0.5O3 M-phase by doping with (Co1/3Nb2/3)4+

Structural evolution and microwave dielectric properties of LiNb_0.6(Ti_1-x[Co_1/3Nb_2/3]_x)_0.5O₃ (.05≤x≤.2) ceramics have been studied in this paper. Although the doped compositions maintain the M-phase solid solutions, compositional fluctuation due to nonuniform dispersion of minor dopants could be observed as x < .05, and trace amount of Li₂TiO₃-based solid solution (Li₂TiO₃ss) secondary phase presents in the x > .05 compositions. The microwave dielectric properties could be remarkably improved by the doping of (Co_1/2Nb_1/2)⁴⁺ in comparison to the undoped counterpart. Optimized microwave dielectric properties with Q × f = ∼6500 GHz, ε_r = ∼74 and τ_f = +8.2 ppm/°C could be obtained at x = .10 after sintering at 1050°C/2 h. The sintering temperature could be further reduced to 900°C/2 h by adding .2 wt% B₂O₃ without affecting significantly its microwave dielectric properties: ε_r = 73, Q × f = 6000 GHz, τ_f = +8.5 ppm/°C. The LiNb_0.6(Ti_1-x[Co_1/3Nb_2/3]_x)_0.5O₃ ceramics obtained in this case exhibit large dielectric permittivity coupled with much improved Q × f values, near zero τ_f, and low sintering temperature simultaneously, which makes it a promising high-k microwave dielectric material for low temperature cofired ceramic applications.     

Improved sinterability and microwave dielectric properties of [Zn0.5Ti0.5]3+-doped ZnAl2O4 spinel solid solution

Low-permittivity ZnAl_2-x(Zn_0.5Ti_0.5)_xO₄ ceramics were synthesized via conventional solid-state reaction method. A pure ZnAl₂O₄ solid-state solution with an Fd-3m space group was achieved at x ≤ 0.1. Results showed that partial substitution of [Zn_0.5Ti_0.5]³⁺ for Al³⁺ effectively lowered the sintering temperature of the ZnAl₂O₄ ceramics and remarkably increased the quality factor (Q × f) values. Optimum microwave dielectric properties (ε_r = 9.1, Q × f = 115,800 GHz and τ_f = −78 ppm/°C) were obtained in the sample with x = 0.1 sintered at 1400°C in oxygen atmosphere for 10 h. The temperature used for the sample was approximately 250°C lower than the sintering temperature of conventional ZnAl₂O₄ ceramics.     

Low loss and good chemical compatibility with silver electrodes of Cu2+-substituted Ba3Ti4Nb4O21 ceramics realizing low temperature co-fired ceramics technology: Crystal structure,vibration modes and chemical bonds studies

New low loss and low-sintering temperature co-fired Ba_3-xCu_xTi₄Nb₄O₂₁ (BCTN, 0 ≤ x ≤ 0.12) ceramics with 0.60 wt% Li₂O-B₂O₃-SiO₂-CaO-Al₂O₃ (LBSCA) glass were prepared by solid-state reaction methodology. This work showed that CuO and LBSCA were effective sintering aid, which improved the densification and decreased sintering temperature. Thus, the excellent microwave dielectric properties of BCTN ceramics (x = 0.08) were obtained after sintering at 925 ℃ with ε_r ~ 44.18, Q×f ~ 17,860 GHz (@ 5.6 GHz) and τ_f ~ 94.76 ppm/℃. Q×f value was increased nearly 3-fold compared to pure BTN ceramics (~ 6090 GHz). Based on the P-V-L bond theory, the Ti-O and Nb-O bonds together contributed greatly to ε_r. The Nb-O bonds was the main factor affecting the internal loss on Q×f. The τ_f closely related to the oxygen octahedron [Ti1/Nb1O₆]. The BCTN ceramics would not react with Ag electrodes, and had great potential to be used in LTCC microwave devices.     

Dielectric properties with high dielectric permittivity and low loss tangent and nonlinear electrical response of sol-gel synthesized Na1/2Sm1/2Cu3Ti4O12 perovskite ceramic

Giant dielectric ceramic, Na_1/2Sm_1/2Cu₃Ti₄O₁₂, was successfully prepared by a modified sol-gel method. X-ray diffraction experiments indicated that a body-centered cubic structure with a space group of Im3 was obtained. Our density functional theory calculations revealed that codoping Na and Sm in the CaCu₃Ti₄O₁₂ structure resulted in charge compensation between Na and Sm ions in this structure, whereas the oxidation states of Cu and Ti were unaltered. Giant dielectric permittivity ～7.21 × 10³ - 8.04 × 10³ and low dielectric loss tangent ～0.045–0.049 were accomplished at a sintering temperature of 1050 °C for 12–18 h. Nonlinear J - E property with breakdown electric field ～5.13 – 5.78 × 10³ V/cm and nonlinear coefficient ～6.08–6.82 were also achieved. The n-type semiconducting grain originated from short-range migrations of mixed Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺ charges. Finally, our charge analysis showed that the occurrence of Cu⁺ and Ti³⁺ was related to the existence of oxygen vacancy in these ceramics.     

Colossal dielectric response and relaxation behavior in novel system of Zr4+ and Nb5+ co-substituted CaCu3Ti4O12 ceramics

In this work, we developed a novel system of isovalent Zr⁴⁺ and donor Nb⁵⁺ co-doped CaCu₃Ti₄O₁₂ (CCTO) ceramics to enhance dielectric response. The influences of Zr⁴⁺ and Nb⁵⁺ co-substituting on the colossal dielectric response and relaxation behavior of the CCTO ceramics fabricated by a conventional solid-phase synthesis method were investigated methodically. Co-doping of Zr⁴⁺ and Nb⁵⁺ ions leads to a significant reduction in grain size for the CCTO ceramics sintered at 1060 °C for 10 h. XRD and Raman results of the CaCu₃Ti_3.8-xZr_xNb_0.2O₁₂ (CCTZNO) ceramics show a cubic perovskite structure with space group Im-3. The first principle calculation result exhibits a better thermodynamic stability of the CCTO structure co-doped with Zr⁴⁺ and Nb⁵⁺ ions than that of single-doped with Zr⁴⁺ or Nb⁵⁺ ion. Interestingly, the CCTZNO ceramics exhibit greatly improved dielectric constant (~10⁵) at a frequency range of 10²–10⁵ Hz and at a temperature range of 20–210 °C, indicating a giant dielectric response within broader frequency and temperature ranges. The dielectric properties of CCTZNO ceramics were analyzed from the viewpoints of defect-dipole effect and internal barrier layer capacitance (IBLC) model. Accordingly, the immensely enhanced dielectric response is primarily ascribed to the complex defect dipoles associated with oxygen vacancies by co-doping Zr⁴⁺ and Nb⁵⁺ ions into CCTO structure. In addition, the obvious dielectric relaxation behavior has been found in CCTZNO ceramics, and the relaxation process in middle frequency regions is attributed to the grain boundary response confirmed by complex impedance spectroscopy and electric modulus.     

Influences of B2O3/CuO additions on the sintering behavior,microstructure and microwave dielectric properties of 6Nd[(Zn0.7Co0.3)0.5Ti0.5]O3–4(Na0.5Nd0.5)TiO3 ceramics

B₂O₃ and CuO were codoped into 6Nd[(Zn_0.7Co_0.3)_0.5Ti_0.5]O₃–4(Na_0.5Nd_0.5)TiO₃ (abbreviated as 6NZCT–4NNT) ceramics as sintering aids. The influences of the sintering aids on the sintering characteristics, microstructure and microwave dielectric properties of the 6NZCT–4NNT ceramics were systematically investigated as a function of the proportion of B₂O₃ and CuO. Codoping could greatly reduce the sintering temperature from 1410 °C to 1150 °C, indicating that B₂O₃/CuO are good sintering aids for 6NZCT–4NNT ceramics. The B₂O₃/CuO sintering aids had no significant impact on the phase purity of the investigated ceramics, even though a solid solution was formed due to Cu²⁺ ion substitution. However, they had evident influences on the surface morphology and grain size. The average grain size was enlarged with increasing amounts of CuO in the B₂O₃/CuO sintering aids. Remarkable deterioration of the microwave dielectric properties for 6NZCT-4NNT ceramics was not observed when codoping an appropriate amount of B₂O₃ and CuO. The 6NZCT–4NNT ceramics codoped with 2.0 mol% B₂O₃ and 2.0 mol% CuO sintered at 1150 °C for 3 h exhibited a homogeneous microstructure and promising microwave dielectric properties: an appropriate dielectric constant (ε_r = 49.37), a high quality factor (QF = 47,295 GHz), and a near-zero temperature coefficient of resonant frequency (TCF = +0.9 ppm/^°C).     

Low-fire processing and microwave dielectric properties of LB glass-doped Ba3.75Nd9.5Ti17.5(Cr0.5Nb0.5)0.5O54 ceramic

The effects of LB glass on the sintering behavior, structure, and dielectric properties for the Ba_3.75Nd_9.5Ti_17.5(Cr_0.5Nb_0.5)_0.5O₅₄ (BNTCN) ceramic were investigated. The results showed that the LB glass, as an effective sintering aid, successfully lowered the sintering temperature of BNTCN ceramic by formation of the liquid phase. Furthermore, the change of the structure and decrease in grain size had influences on the electrical conductivity, thermal stability, and microwave dielectric properties for the BNTCN ceramics doped LB glass. Finally, the excellent microwave dielectric properties with ε_r = 73.4, Q × f = 5277 GHz, and τ_f = +7.1 ppm/°C were obtained for samples sintered at 950°C when x = 5, indicating the BNTCN ceramic doped with 5 wt% LB glass is a promoting LTCC material.