Low temperature sintering of the Ba2Ti9O20 ceramics using B2O3/CuO and BaCu(B2O5) additives

The effects of B₂O₃/CuO and BaCu(B₂O₅) additives on the sintering temperature and microwave dielectric properties of Ba₂Ti₉O₂₀ ceramics were investigated. The B₂O₃ added Ba₂Ti₉O₂₀ ceramics were not able to be sintered below 1000 °C. However, when both CuO and B₂O₃ were added, they were sintered below 900 °C and had the good microwave dielectric properties. It was suggested that a liquid phase with the composition of BaCu(B₂O₅) was formed during the sintering and assisted the densification of the Ba₂Ti₉O₂₀ ceramics at low temperature. BaCu(B₂O₅) powders were produced and used to reduce the sintering temperature of the Ba₂Ti₉O₂₀ ceramics. Good microwave dielectric properties of Qxf = 16,000 GHz, ɛ_r = 36.0 and τ_f = 9.11 ppm/°C were obtained for the Ba₂Ti₉O₂₀ ceramics containing 10.0 mol% BaCu(B₂O₅) sintered at 875 °C for 2 h.     

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.     

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.     

Effect of B2O3 on the sintering and microwave dielectric properties of M-phase LiNb0.6Ti0.5O3 ceramics

The effect of B₂O₃ addition on the sintering, microstructure and the microwave dielectric properties of LiNb_0.6Ti_0.5O₃ ceramics have been investigated. It is found that low-level doping of B₂O₃ (≤2 wt.%) can significantly improve the densification and dielectric properties of LiNb_0.6Ti_0.5O₃ ceramics. Due to the liquid phase effect of B₂O₃ addition, LiNb_0.6Ti_0.5O₃ ceramics could be sintered to a theoretical density higher than 95% even at 880 °C. No secondary phase was observed for the B₂O₃-doped ceramics. There is no obvious degradation in dielectric properties for the ceramics with B₂O₃ additions. In the case of 1 wt.% B₂O₃ addition, the ceramics sintered at 880 °C show good microwave dielectric properties of ɛ_r = 70, Q × f = 5400 GHz, τ_f = −6.39 ppm/°C. It represents that the ceramics could be promising for multilayer low-temperature co-fired ceramics (LTCC) applications.     

Anti-reduction of Ti4+ in Ba4.2Sm9.2Ti18O54 ceramics by doping with MgO,Al2O3 and MnO2

The anti-reduction of Ti⁴⁺ ions in Ba_4.2Sm_9.2Ti₁₈O₅₄ (BST) ceramics at high sintering temperature over 1300 °C was investigated. MgO, Al₂O₃ and MnO₂ were added separately to suppress the reduction of Ti⁴⁺ ions so as to improve the microwave dielectric properties of BST ceramics. The microstructure of BST ceramics was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) was used to study the electroconductivity of BST ceramics and valency changes of Ti ions. The results showed that MgO or Al₂O₃, when acting as an acceptor, could effectively suppress the reduction of Ti⁴⁺ ions and significantly improve the Q × f values of BST ceramics at the cost of dielectric constant. Meanwhile, MnO₂ as an oxidant had also improved the Q × f values but with no decrease in dielectric constant. Excellent microwave dielectric properties were achieved in Ba_4.2Sm_9.2Ti₁₈O₅₄ ceramics doped with 0.2 wt.% Al₂O₃ sintered at 1340 °C for 3 h: ?_r = 76.9, Q × f = 10,120 GHz and τ_f  = ?22.7 ppm/°C.     

Low sintering BaNd2Ti4O12 microwave ceramics prepared by CuO thin layer coated powder

Recently, BaO–Nd₂O₃–TiO₂ systems are widely studied for microwave applications because of their high dielectric constant and high quality factor. However, pure BaNd₂Ti₄O₁₂ ceramics without additives have to be sintered above 1300 °C to achieve densification. Copper oxide has been known as a good sintering aid for electronic ceramics and less reactive toward silver. We have introduced the CuO into BaNd₂Ti₄O₁₂ by modifying the surface of BaNd₂Ti₄O₁₂ by CuO thin layer on the calcined powder instead of mixing CuO directly with BaNd₂Ti₄O₁₂ powder. The process reduces the amount of sintering aid and minimized the negative impact of sintering aid on dielectric properties such as quality factor. The CuO precursor solution of Cu(CH₃COO)₂, Cu(NO₃)₂ and CuSO₄, were used to prepare CuO thin layer. They were investigated individually to determine their effects on the densification, crystalline structure, microstructure and microwave dielectric properties of BaNd₂Ti₄O₁₂. The CuSO₄ coated BaNd₂Ti₄O₁₂ sintered at 1150 °C has exhibited better dielectric properties than those of CuO doped BaNd₂Ti₄O₁₂ (k, 62.5 versus 61.2; Q × f, 11,500 GHz versus 10,500 GHz). The thin layer dopant coating process has been found to be a very effective way to lower ceramic sintering temperature without scarifying its dielectric properties.     

Effect of B2O3 and CuO additives on the sintering temperature and microwave dielectric properties of Ba(Zn1/3Nb2/3)O3 ceramics

The B₂O₃ added Ba(Zn_1/3Nb_2/3)O₃ (BBZN) ceramic was sintered at 900 °C. BaB₄O₇, BaB₂O₄, and BaNb₂O₆ second phases were found in the BBZN ceramic. Since BaB₄O₇ and BaB₂O₄ second phases have an eutectic temperature around 900 °C, they might exist as the liquid phase during sintering at 900 °C and assist the densification of the BZN ceramics. Microwave dielectric properties of dielectric constant (ɛ_r) = 32, Q × f = 3500 GHz, and temperature coefficient of resonance frequency (τ_f) = 20 ppm/°C were obtained for the BZN with 5.0 mol% B₂O₃ sintered at 900 °C for 2 h. The BBZN ceramics were not sintered below 900 °C and the microwave dielectric properties of the BBZN ceramics sintered at 900 °C were very low. However, when CuO was added, BBZN ceramic was well sintered even at 875 °C. The liquid phase related to the BaCu(B₂O₅) second phase could be responsible for the decrease of sintering temperature. Good microwave dielectric properties of ɛ_r = 36, Q × f = 19,000 GHz and τ_f = 21 ppm/°C can be obtained for CuO doped BBZN ceramics sintered at 875 °C for 2 h.     

(Cu1/3Nb2/3)4+ ionic substituting effects,low-temperature sintering behaviors,and improved temperature stability of Ba3Nb4Ti4O21 microwave dielectric ceramics

In this study, (Cu_1/3Nb_2/3)⁴⁺ complex cation and BaO–ZnO–B₂O₃ glass frit were adopted to solve the high sintering temperature and poor temperature stability of Ba₃Nb₄Ti₄O₂₁ ceramics. It is shown that pure Ba₃Nb₄Ti₄O₂₁ phase was formed when Ti site was partially replaced by (Cu_1/3Nb_2/3)⁴⁺ cation. The increasing number of dopants decreases the dielectric polarizability, correspondingly, the dielectric constant and temperature coefficient of the resonance frequency values are reduced consistently. The variation of the Q × f value is determined by internal ionic packing fraction and external sintering densification. The (Cu_1/3Nb_2/3)⁴⁺ cation effectively decreases the suitable sintering temperature from 1200 to 1050 °C while greatly improving the temperature stability. BaO–ZnO–B₂O₃ glass was used to further improve the low-temperature sintering characteristics of Ba₃Nb₄Ti₄O₂₁ ceramics. It is proven that the addition of glass frits effectively decreases the temperature to 925 °C with combinational excellent microwave dielectric properties: ε_r ～55.6, Q × f ～5700 GHz, τ_f ～3 ppm/^°C, making the Ba₃Nb₄Ti₄O₂₁ ceramics promising in the applications of low-temperature cofired ceramic technology.     

Low-temperature sintering of Ti1−xCux/3Nb2x/3O2 (x = 0.23) microwave dielectric ceramics with CuO and B2O3 addition

The influence of CuO and B₂O₃ addition on the sintering behavior, microstructure and microwave dielectric properties of Ti_1?xCu_x/3Nb_2x/3O₂ (TCN, x = 0.23) ceramic have been investigated. It was found that the addition of CuO and B₂O₃ successfully reduced the sintering temperature of TCN ceramics from 950 to 875 °C. X-ray diffraction studies showed that addition of CuO-B₂O₃ has no effect on the phase composition. The TCN ceramics with 0.5 wt% CuO-B₂O₃ addition showed a high dielectric constant of 95.63, τ_f value of + 329 ppm/°C and a good Q × f value of 8700 GHz after sintered at 875 °C for 5 h, cofirable with silver electrode.     

Microwave dielectric properties and microstructures of Nb2O5-Zn0.95Mg0.05TiO3 + 0.25TiO2 ceramics with Bi2O3 addition

The effects of Bi₂O₃ addition on the microwave dielectric properties and the microstructures of Nb₂O₅-Zn_0.95Mg_0.05TiO₃ + 0.25TiO₂ (Nb-ZMT′) ceramics prepared by conventional solid-state routes have been investigated. The results of X-ray diffraction (XRD) indicate the presence of four crystalline phases, ZnTiO₃, TiO₂, Bi₂Ti₂O₇, and (Bi_1.5Zn_0.5)(Ti_1.5Nb_0.5)O₇ in the sintered ceramics, depending upon the amount of Bi₂O₃ addition. In addition, in order to confirm the existence of (Bi_1.5Zn_0.5)(Ti_1.5Nb_0.5)O₇ phase in the samples, the microstructure of Nb-ZMT′ ceramic with 5 wt.% B₂O₃ addition was analyzed by using a transmission electron micrograph. The dielectric constant of Nb-ZMT′ samples was higher than ZMT′ ceramics. The Nb-ZMT′ ceramic with 5 wt.% Bi₂O₃ addition exhibits the optimum dielectric properties: Q × f = 12,000 GHz, ?_r = 30, and τ_f = ?12 ppm/°C. Unlike the ZMT′ ceramic sintered at 900 °C, the Nb-ZMT′ ceramics show higher Q value and dielectric constant. Moreover, there is no Zn₂TiO₄ existence at 960 °C sintering. To understand the co-sinterability between silver electrodes and the Nb-ZMT′ dielectrics, the multilayer samples are prepared by multilayer thick film processing. The co-sinterability (900 °C) between silver electrode and Nb-ZMT′ dielectric are well compatible, because there are no cracks, delaminations, and deformations in multilayer specimens.     

Li4Mg3Ti2O9: A novel low-loss microwave dielectric ceramic for LTCC applications

Low-loss novel Li₄Mg₃Ti₂O₉ dielectric ceramics with rock-salt structure were prepared by a conventional solid-state route. The crystalline structure, chemical bond properties, infrared spectroscopy and microwave dielectric properties of the abovementioned system were initially investigated. It could be concluded from this work that the extrinsic factors such as sintering temperatures and grain sizes significantly affected the dielectric properties of Li₄Mg₃Ti₂O₉ at lower sintering temperatures, while the intrinsic factors like bond ionicity and lattice energy played a dominant role when the ceramics were densified at 1450 °C. In order to explore the origin of intrinsic characteristics, complex dielectric constants (ε^’ and ε^’’) were calculated by the infrared spectra, which indicated that the absorptions of phonon oscillation predominantly effected the polarization of the ceramics. The Li₄Mg₃Ti₂O₉ ceramics sintered at 1450 °C exhibited excellent properties of ε_r=15.97, Q·f=135,800 GHz and τ_f=−7.06 ppm/°C. In addition, certain amounts of lithium fluoride (LiF) were added to lower the sintering temperatures of matrix. The Li₄Mg₃Ti₂O₉−3 wt% LiF ceramics sintered at 900 °C possessed suitable dielectric properties of ε_r=15.17, Q·f =42,800 GHz and τ_f=−11.30 ppm/°C, which made such materials promising for low temperature co-fired ceramic applications (LTCC).     

Silver cofirability differences between Bi1.5Zn0.92Nb1.5O6.92 and Zn3Nb2O8

We have investigated systematically the differences of silver cofirability and microwave dielectric properties between Zn₃Nb₂O₈ and Bi_1.5Zn_0.92Nb_1.5O_6.92 (BZN). Two type dopants: 0.29BaCO₃–0.71CuO (BC) and 0.81MoO₃–0.19CuO (MC) were used in Zn₃Nb₂O₈ and Bi_1.5Zn_0.92Nb_1.5O_6.92 ceramics so they can be cofired with silver. The BC-doped ceramics in general have better dielectric properties than those of MC-doped ceramics. The BC-doped Zn₃Nb₂O₈ exhibits better dielectric properties than those of BC-doped BZN (k = 14.7, Q × f = 8200 GHz versus k = 120.1, Q × f = 1050 GHz). For silver compatibility study, the interfacial behaviors between microwave dielectric materials and silver were investigated by using X-ray diffractometer, scanning electronic microscope, and electronic probe microanalyzer. No new crystalline phase and no silver migration behavior were found in the BC-doped Zn₃Nb₂O₈ ceramics cofired with silver, but slight silver migration was detected for BC-doped BZN. But slight silver migration was detected for MC-doped Zn₃Nb₂O₈ and BZN ceramics cofired with silver. Therefore, the good overall properties of BC-doped Zn₃Nb₂O₈ are suitable for microwave applications.     

Effect of Li2O–V2O5 on the low temperature sintering and microwave dielectric properties of Li1.0Nb0.6Ti0.5O3 ceramics

Li₂O–Nb₂O₅–TiO₂ based ceramic systems have been the candidate materials for LTCC application, due to their high dielectric constant and Q × f value and controllable temperature coefficient in the microwave region. However, the sintering temperature was relatively higher (above 1100 °C) for practical application. In this study, dielectric properties of Li_(1+x−y)Nb_(1−x−3y)Ti_(x+4y)O₃ solid solution were studied with different x and y contents and among them, the Li_1.0Nb_0.6Ti_0.5O₃ composition (x = 0.1, y = 0.1) was selected, due to its reasonable dielectric properties to determine the possibility of low temperature sintering. The effects of 0.17Li₂O–0.83V₂O₅, as a sintering agent, on sinterability and microwave dielectric properties of Li_1.0Nb_0.6Ti_0.5O₃ ceramics were investigated as a function of the sintering agent content and sintering temperature. With addition of 0.17Li₂O–0.83V₂O₅ above 0.5 wt%, the specimens were well densified at a relatively lower temperature of 850 °C. Only slight decrease in apparent density was observed with increasing 0.17Li₂O–0.83V₂O₅ content above 0.75 wt%. In the case of 0.5 wt% 0.17Li₂O–0.83V₂O₅ addition, the values of dielectric constant and Q × f reached maximum. Further addition caused inferior microstructure, resulting in degraded dielectric properties. For the specimens with 0.5 wt% 0.17Li₂O–0.83V₂O₅ sintered at 850 °C, dielectric constant, Q × f and TCF values were 64.7, 5933 GHz and 9.4 ppm per °C, respectively.     

Effect of dopants on synthesis of BaTi4O9 and Ba2Ti9O20 ceramics prepared by reaction-sintering process

The effect of dopants on BaTi₄O₉ (BT4) and Ba₂Ti₉O₂₀ (B2T9) ceramics by the reaction-sintering process was investigated. CuO addition is more effective in lowering the sintering temperature of BT4 and B2T9 ceramics. MnO₂ and CuO addition are effective to obtain temperature stable BT4 ceramics. With MnO₂ addition, Q × f of BT4 ceramics could be raised. ZrO₂ addition is effective to obtain B2T9 ceramics with higher dielectric constant. With CuO addition, τ_f of B2T9 ceramics shifted toward negative values and 0 ppm/°C could be obtained. Optimum properties in BT4 doped with MnO₂ of ɛ_r = 37.1, Q × f = 51,200 GHz (at 7 GHz) and τ_f = 0 ppm/°C and in B2T9 doped with ZrO₂ of ɛ_r = 37.9, Q × f = 39,700 GHz (at 7 GHz) and τ_f = 5.9 ppm/°C were obtained.     

Microwave dielectric properties of Ca(Li1/4Nb3/4)O3–CaTiO3 ceramic systems

The microwave dielectric properties of Ca(Li_1/4Nb_3/4)O₃–CaTiO₃ ceramics have been investigated with regard to calcination temperature and the amount of CaTiO₃ additive. Ca(Li_1/4Nb_3/4)O₃ ceramics with an orthorhombic crystal structure can be synthesized by the conventional mixed oxide method by calcining at 750 °C and sintering at 1275 °C. The dielectric constant (ɛ_r), quality factor (Q × f₀) and temperature coefficient of resonant frequency (τ_f) for Ca(Li_1/4Nb_3/4)O₃ ceramics are 26, 13,000 GHz and −49 ± 2 ppm/°C, respectively. With increase in the CaTiO₃ content, ɛ_r and τ_f are increased and the quality factor decreased due to the solid-solution formation between Ca(Li_1/4Nb_3/4)O₃ and CaTiO₃. The 0.7Ca(Li_1/4Nb_3/4)O₃–0.3CaTiO₃ ceramic exhibits ɛ_r of 44, quality factor (Q × f₀) of 12,000 GHz and τ_f of −9 ± 1 ppm/°C.     

Low temperature firing of BiSbO4 microwave dielectric ceramic with B2O3–CuO addition

The influence of B₂O₃–CuO addition on the sintering behavior, phase composition, microstructure and microwave dielectric properties of BiSbO₄ ceramic have been investigated. The BiSbO₄ ceramics can be well densified to approach above 95% theoretical density in the sintering temperature range from 840 to 960 °C as the addition amount of B₂O₃–CuO increases from 0.6 to 1.2 wt.%. Sintered ceramic samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The microwave permittivity ?_r saturated at 19–20 and Qf values varied between 33,000 and 46,000 GHz while temperature coefficient of resonant frequency shifting between ?70 and ?60 ppm/°C at sintering temperature around 930 °C. Lowering sintering temperature of BiSbO₄ ceramics makes it possible for application in low temperature co-fired ceramic technology.     

Microwave dielectric properties and compatibility with silver electrode of novel low-fired Ba4CuTi11O27 ceramic

A novel low-fired microwave dielectric ceramic with composition of Ba₄CuTi₁₁O₂₇ was prepared by a conventional solid-state reaction method. A single-phase Ba₄CuTi₁₁O₂₇ ceramic could be well densified after sintering above 950 °C for 4 h in air. A refinement using X-ray powder diffraction data was carried out in the Rietveld method using the parameters of Ba₄Ti₁₂O₂₇ as a starting model. Ba₄CuTi₁₁O₂₇ ceramic sintered at 975 °C has a monoclinic structure (C12/m1) with lattice parameters of a=19.8061(4) Å, b=11.4456(2) Å, c=9.9131(2) Å, β=108.8988(15) Å, V=2126.08(8) Å³, Z=4. The Ba₄CuTi₁₁O₂₇ ceramics exhibited a low sintering temperature (~975 °C) and good microwave dielectric properties with Q×f value of 15,040 GHz, ε_r of 36.3 and τ_f value 11.9 ppm/°C. More importantly, the Ba₄CuTi₁₁O₂₇ dielectrics demonstrated good chemical compatibility with Ag when sintered at 950 °C, keeping excellent microwave dielectric properties with Q×f=12,130 GHz, ε_r=36.1, τ_f=12.1 ppm/°C, which indicates that Ba₄CuTi₁₁O₂₇ ceramic is a candidate for LTCC devices.     

Effect of CuO/MnO additives on microstructure and microwave dielectric properties of 3ZrO2-3TiO2-ZnNb2O6 ceramics

The effect of CuO/MnO additives on phase composition, microstructures, sintering behavior, and microwave dielectric properties of 3ZrO₂-3TiO₂-ZnNb₂O₆ (3Z-3T-ZN) ceramics prepared by conventional solid-state route were systematically investigated. CuO/MnO doped ceramics exhibited a main phase of α-PbO₂-structured ZrTi₂O₆ and a secondary phase of rutile TiO₂. SEM results showed that the grain size of MnO doped ceramics became larger with increasing amount of dopants. The presence of CuO/MnO additives effectively reduced the sintering temperature of 3Z-3T-ZN ceramics to 1220 °C. MnO doped into ceramics could enhance the Q×f values significantly. The 0.5 wt% CuO doped 3Z-3T-ZN ceramics with 0.5 wt% of MnO, sintered at 1220 °C for 4 h, was measured to show superior microwave dielectric properties, with an ε_r of 41.02, a Q×f value of 44,230 GHz (at 5.2 GHz), and τ_f value of +2.32 ppm/°C.     

Sintering behavior and microwave dielectric characteristics of BaO–Sm2O3–4TiO2 ceramics with B2O3 and BaB2O4 addition

We studied the low temperature sintering and the reaction in BaO–Sm₂O₃–4TiO₂ ceramics with boron-based additives for the application to microwave dielectric devices. The amount of the boride glasses of B₂O₃ and BaB₂O₄ was varied from 1 to 10 wt.% and the green compacts were sintered in the temperature range of 900–1200 °C for 2 h. When B₂O₃ was added, second phases of Sm₂Ti₂O₇, BaTi(BO₃)₂, Ba₂Ti₉O₂₀, and TiO₂ were formed, while BaB₂O₄ addition resulted in the formation of BaSm₂Ti₄O₁₂ single phase without second phases. On the basis of these results, it is regarded that the B₂O₃ is a reactive glass and the BaB₂O₄ is a non-reactive glass. The second-phase development, sintering behavior and microwave dielectric characteristics of BaO–Sm₂O₃–4TiO₂ ceramics were examined.     

Synthesis and dielectric anomalies of CdCu3Ti4O12 ceramics

CdCu₃Ti₄O₁₂ ceramics were successfully synthetized by the conventional solid-state reaction method. The influences of sintering parameters on phase structure, microstructure and dielectric properties were investigated systematically. CdCu₃Ti₄O₁₂ ceramics sintered at 1020 °C for 15 h exhibited high temperature stability and outstanding dielectric properties, evidenced by the △C_T/C_25 °C ranges from −14.8% to 12.1% measured from −55 to 125 °C at 1 kHz, and the giant dielectric constant ε′=2.4×10⁴ as well as dielectric loss tanδ=0.072. Four dielectric anomalies were evidenced in dielectric temperature spectra and the related physical mechanisms were discussed in detail. The oxygen vacancies play an important role in dielectric anomalies in the high temperature range.