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.     

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.     

Microwave dielectric properties of LiNb3O8 ceramics with TiO2 additions

The microwave dielectric properties of LiNb₃O₈ ceramics were investigated as a function of the sintering temperature and the amount of TiO₂ additive. LiNb₃O₈ ceramics, which were calcined at 750 °C and sintered at 1075 °C for 2 h, showed a dielectric constant (ɛ_r) of 34, a quality factor (Q × f₀) of 58,000 GHz and a temperature coefficient of resonance frequency (τ_f) of −96 ppm/°C, respectively. The density of the samples influenced the properties of these properties. As the TiO₂ content increased in the LiNb₃O₈–TiO₂ system, ɛ_r and τ_f of the material were increased due to the mixing effect of TiO₂ phase, which has higher dielectric constant and larger positive τ_f. The 0.65LiNb₃O₈–0.35TiO₂ ceramics showed a dielectric constant ɛ_r of 46.2, a quality factor (Q × f₀) of 5800 GHz and a temperature coefficient of resonance frequency τ_f of near to 0 ppm/°C.     

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.     

Effect of BaCu(B2O5) on the sintering and microwave dielectric properties of Ca0.4Li0.3Sm0.05Nd0.25TiO3 ceramics

The sintering behaviors and microwave dielectric properties of the Ca_0.4Li_0.3Sm_0.05Nd_0.25TiO₃ (abbreviated CLSNT) ceramics with different amounts of BaCu(B₂O₅) addition were investigated in this paper. Adding BaCu(B₂O₅) to CLSNT lowered its sintering temperature from 1300 °C to 925 °C. No secondary phase was observed in the CLSNT ceramics and complete solid solution of the complex perovskite phase was confirmed. The CLSNT ceramics with small amounts of BaCu(B₂O₅) addition could be well sintered at 925 °C without much degradation in the microwave dielectric properties. Especially, the 1.75 wt.% BaCu(B₂O₅)-doped CLSNT ceramic sample sintered at 925 °C for 3 h had optimum microwave dielectric properties of ε_r = 93.5 ± 3.2, Q × f = 6486 ± 434 GHz, and τ_f = 5 ± 1.5 ppm/°C (at 3–4 GHz), enabling it a promising candidate material for LTCC applications. Obviously, BaCu(B₂O₅) could be a suitable sintering aid to facilitate the densification and microwave dielectric properties of the CLSNT ceramics.     

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.     

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.     

Effects of sintering parameters and Nd doping on the microwave dielectric properties of Y2O3 ceramics

Y₂O₃ ceramics with good dielectric properties were prepared via co-precipitation reaction and subsequent sintering in a muffle furnace. The effects of Nd doping and sintering temperature on microwave dielectric properties were studied. With the increase in sintering temperature, the density, quality factor (Q×f), and dielectric constant (ε_r) values of pure Y₂O₃ ceramics increased to the maximum and then gradually decreased. The Y₂O₃ ceramics sintered at 1500 °C for 4 h showed optimal dielectric properties: ε_r=10.76, Q×f=82, 188 GHz, and τ_f=−54.4 ppm/°C. With the addition of Nd dopant, the Q×f values, ε_r, and τ_f of the Nd: Y₂O₃ ceramics apparently increased, but excessive amount degraded the quality factor. The Y₂O₃ ceramics with 2 at% Nd₂O₃ sintered at 1460 °C displayed good microwave dielectric properties: ε_r=10.4, Q×f=94, 149 GHz and τ_f=−46.2 ppm/°C.     

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.     

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).     

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.     

Microwave dielectric properties of novel temperature stable high Q Li2Mg1−xZnxTi3O8 and Li2A1−xCaxTi3O8 (A = Mg,Zn) ceramics

The Li₂Mg_1?xZn_xTi₃O₈ (x = 0–1) and Li₂A_1?xCa_xTi₃O₈ (A = Mg, Zn and x = 0–0.2) ceramics are synthesized by solid-state ceramic route and the microwave dielectric properties are investigated. The Li₂MgTi₃O₈ ceramic shows ?_r = 27.2, Q_u × f = 42,000 GHz, and τ_f = (+)3.2 ppm/°C and Li₂ZnTi₃O₈ has ?_r = 25.6, Q_u × f = 72,000 GHz, and τ_f = (?)11.2 ppm/°C respectively when sintered at 1075 °C/4 h. The Li₂Mg_0.9Zn_0.1Ti₃O₈ dielectric ceramic composition shows the best dielectric properties with ?_r = 27, Q_u × f = 62,000 GHz, and τ_f = (+)1.1 ppm/°C. The effect of Ca substitution on the structure, microstructure and microwave dielectric properties of Li₂A_1?xCa_xTi₃O₈ (A = Mg, Zn and x = 0–0.2) has also been investigated. The materials reported in this paper are excellent in terms of dielectric properties and cost of production compared to commercially available high Q dielectric resonators.     

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.     

Parallel preparation and properties investigation on Li2O-Nb2O5-TiO2 microwave dielectric ceramics

A parallel preparation method was developed using dry powders as starting materials to synthesize multi-compositional microwave dielectric ceramics. The Li₂O-Nb₂O₅-TiO₂ ternary system was investigated as a model material. The validity of the parallel ceramic preparation process was confirmed by synthesizing a group of LiNb_0.6Ti_0.5O₃ ceramics in parallel, which showed the same crystalline structure and close dielectric properties. The ceramic libraries with M-phase-rich samples and Li₂TiO₃-rich samples were prepared using the parallel process, and the microwave dielectric properties and crystal phases were investigated systematically. An excellent microwave ceramic with a composition of 0.55Li₂O-0.05Nb₂O₅-0.40TiO₂ was obtained, which has a dielectric constant of 18.4 and a high quality value (Q × f) of 79000 GHz. This parallel process can be applied extensively to explore a variety of bulk ceramic libraries for discovering new functional materials with high performances.     

Effect of Al2O3 on the structure and microwave dielectric properties of Ca0.7Ti0.7La0.3Al0.3O3

The effect of excess Al₂O₃ on the densification, structure and microwave dielectric properties of Ca_0.7Ti_0.7La_0.3Al_0.3O₃ (CTLA) was investigated. CTLA ceramics were prepared using the conventional mixed oxide route. Excess Al₂O₃ in the range of 0.1–0.5 wt% was added. It was found that Al₂O₃ improved the densification. A phase rich in Ca and Al was found in the microstructure of Al₂O₃ doped samples. Additions of Al₂O₃ coupled with the slow cooling after sintering improved the microwave dielectric properties. CTLA ceramics with 0.25 wt% Al₂O₃ cooled at 5 °C/h showed high density and a uniform grain structure with ɛ_r = 46, Q × f = 38,289 and τ_f = +12 ppm/°C at 4 GHz. XRD and TEM examinations showed the presence of (1 1 2) and (1 1 0) type twins arising from a⁻a⁻c⁺ tilt system with the presence of anti-phase domain boundaries from the displacement of A-site cations of the orthorhombic perovskite structure.     

The effect of sintering temperature and time on microwave properties of Sm(Zn1/2Ti1/2)O3 ceramics for resonators

The microwave dielectric properties of Sm(Zn_1/2Ti_1/2)O₃ ceramics have been investigated. Sm(Zn_1/2Ti_1/2)O₃ ceramics were prepared by conventional solid-state route with various sintering temperatures and times. The prepared Sm(Zn_1/2Ti_1/2)O₃ exhibited a mixture of Zn and Ti showing 1:1 order in the B-site. Higher sintered density of 7.01 g/cm³ can be produced at 1310 °C for 2 h. The dielectric constant values (ɛ_r) of 22–31 and the Q × f values of 4700–37,000 (at 8 GHz) can be obtained when the sintering temperatures are in the range of 1250–1370 °C for 2 h. The temperature coefficient of resonant frequency τ_f was a function of sintering temperature. The ɛ_r value of 31, Q  ×  f value of 37,000 (at 8 GHz) and τ_f value of −19 ppm/°C were obtained for Sm(Zn_1/2Ti_1/2)O₃ ceramics sintered at 1310 °C for 2 h. For applications of high selective microwave ceramic resonator, filter and antenna, Sm(Zn_1/2Ti_1/2)O₃ is proposed as a suitable material candidate.     

Low temperature sintering of BaCu(B2O5)-added BaO–Re2O3–TiO2 (Re = Sm,Nd) ceramics

The sintering temperature of BaSm₂Ti₄O₁₂ (BST) and BaNd₂Ti₅O₁₄ (BNT) ceramics was approximately 1350 °C and decreased to 875 °C with the addition of BaCu(B₂O₅) (BCB) ceramic powder. The presence of the liquid phase was responsible for the decrease of the sintering temperature. The liquid phase is considered to have a composition similar to the BaO-deficient BCB. The bulk density and dielectric constant (ɛ_r) of the specimens increased and reached saturated value with increasing BCB content. 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 Q × f = 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. Moreover, the BST and BNT ceramics containing BCB show good compatibility with silver metal.     

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 of La3Ti2TaO11 ceramics with perovskite-like layered structure

The first characterization of the microwave dielectric properties of the La₃Ti₂TaO₁₁ ceramics is presented. An ordinarily sintered ceramic at 1560 °C exhibits good microwave dielectric properties with ?_r = 46, Q × f = 7500 GHz and τ_f = ?47 ppm/°C. An alternative approach to tailor the temperature coefficient of resonate frequency of La₃Ti₂TaO₁₁ ceramics is also presented. Textured La₃Ti₂TaO₁₁ ceramics were fabricated using spark plasma sintering (SPS). By controlling the sintering temperature, orientation degree increased together with the steadily increase in ?_r and Q × f. A noteworthy change in τ_f from ?43.1 ppm/°C to ?13.6 ppm/°C with increasing orientation degree was observed. These results suggest that grain-orientation control was an effective way to tailor the microwave dielectric properties of La₃Ti₂TaO₁₁ ceramics.     

Low-temperature sintering and microwave dielectric properties of Nd(Co1/2Ti1/2)O3 ceramics using glass addition of oxides

The microstructures and microwave dielectric characteristics of complex perovskite Nd(Co_1/2Ti_1/2)O₃ ceramics with 60P₂O₅–15ZnO–5La₂O₃–5Al₂O₃–5Na₂O–5MgO–5Yb₂O₃ (PZLANMY) additions (1–4 wt%) prepared through the conventional solid-state route were investigated. It was found that Nd(Co_1/2Ti_1/2)O₃ ceramics can be sintered at 1210 °C owing to the sintering aid of PZLANMY-glass addition. At 1300 °C, Nd(Co_1/2Ti_1/2)O₃ ceramics with 1 wt% of PZLANMY-glass addition possess a dielectric constant (ε_r) of 27, a Q×f value of 64,000 GHz and a temperature coefficient of resonant frequency (τ_f) of ?29 ppm/°C. The PZLANMY-glass doped Nd(Co_1/2Ti_1/2)O₃ ceramics can find applications in microwave devices that require low sintering temperature.