Haishen Ren

Low temperature sintering process, phase evolution and dielectric properties of BaTi4O9-filled B–La–Mg–Ti–O glass/ceramic composites

Low temperature co-fired ceramics composite is fabricated by mixing B2O3–La2O3–MgO–TiO2 (BLMT) glass matrix with BaTi4O9 ceramic filler and the influence of the filler on sintering behavior, phase composition, microstructure and dielectric properties of the composite is investigated. The results show that the densification of composites can be achieved at 860xa0°C for 20xa0min by three-stage reactive liquid assisted sintering process, consisting of glass redistribution and local grains rearrangement, viscous flow, and solid state sintering and closure of pores. The XRD patterns exhibit that the main phase of all samples is LaBO3 phase formed from the crystallization of BLMT glass and the secondary phases have changed due to chemical reaction between BLMT glass and BaTi4O9 forming two new phases BaTi(BO3)2 and TiO2 during sintering. Meanwhile, the microstructure results indicate that the reaction helps to eliminate the closed pores in composites. As the filler is increased, the dielectric constant and quality factor firstly increases and then decreases, while the temperature coefficient of resonant frequency increases. Typically, the 30xa0wt% BaTi4O9-filled BLMT glass composite sintered at 860xa0°C for 20xa0min displays dielectric properties of εεru2009=u200920.49, Qu2009×u2009fu2009=u200924000xa0GHz and ττfu2009=u2009+145xa0ppm/°C.

The influence of BBZ glass on phase evolution, sintering behavior and dielectric properties of BaTi4O9 ceramics

A low temperature co-fired ceramic (LTCC) material has been fabricated by mixing BaTi4O9 ceramic powder with a BaO–B2O3–ZnO (BBZ) glass and sintering the mixture at 925xa0°C/2xa0h. The influence of the BBZ glass on sintering behavior, phase evolution, microstructure and microwave dielectric properties of the BaTi4O9-based LTCC material has been investigated. The results show that the BBZ glass can significantly lower the sintering temperature of the BaTi4O9 ceramics from 1350xa0°C to below 950xa0°C. The XRD patterns exhibit that remarkable chemical reactions happen between BaTi4O9 and the BBZ glass during sintering, forming two new phases BaTi(BO3)2 and Ba4Ti13O30 in the material. As BBZ glass is increased from 5 to 30xa0wt%, BaTi(BO3)2 phase gradually dominates the material and BaTi4O9 decreases and almost disappears at the end. At the same time, the dielectric constant decreases from 33 to 25, the temperature coefficient of resonant frequency decreases from +25.44 to −3.19xa0ppm/°C, and the quality factor firstly increases and then decreases with the peak value of 29500xa0GHz. The changes of the dielectric properties with the BBZ glass content are correlated with the phase evolution of the material during sintering. Typically, the BaTi4O9-based ceramics with 25xa0wt% BBZ glass sintered at 925xa0°C for 2xa0h displays excellent comprehensive properties with a maximum density of 4.33xa0g/cm3, the dielectric constant of 27.08, quality factor of 29,500xa0GHz and temperature coefficient of resonant frequency of +3.5xa0ppm/°C. In addition, the good chemical compatibility of this material with Ag electrode makes it a potential candidate for LTCC technology.

Investigation of Li 2 Zn 3 Ti 4 O 12 -based temperature stable dielectric ceramics for LTCC applications

A low temperature co-fired ceramic (LTCC) was fabricated at 910xa0°C /2xa0h from the powder mixture of Li2Zn3Ti4O12, TiO2 and a B2O3–La2O3–MgO–TiO2 glass (BLMT), and the influence of TiO2 on microstructure and dielectric properties of the composite was investigated in the composition range (wt%) of 20BLMT–(80u2009−u2009x)Li2Zn3Ti4O12–xTiO2 (xu2009=u20090, 2.5, 5, 7.5, 9 and 10). The results showed that all samples consisted of Li2Zn3Ti4O12, TiO2, LaBO3 and LaMgB5O10 phase. And LaBO3, LaMgB5O10 and a small amounts of TiO2 were crystallized from BLMT glass during sintering process. As x increases, dielectric constant and temperature coefficient of resonance frequency of the composites demonstrated gradually increase, whereas the quality factor of the sample of xu2009=u20090xa0wt% was about 41,500xa0GHz and the ones maintained stable at a high level of 49,000–51,000xa0GHz for other samples. The composite with xu2009=u20099xa0wt% had an optimal microwave dielectric properties with the dielectric constant of 20.2, quality factor of 50,000xa0GHz and temperature coefficient of resonant frequency of −u20090.33xa0ppm/°C.

Effects of B2O3 additive on ultra-low-loss Mg4Ta2O9 microwave dielectric ceramics

The effects of B2O3 additive on the phase composition and microwave dielectric properties of Mg4Ta2O9 ceramic were investigated by solid state reaction method. The results showed that the B2O3 additive can lower sintering temperatures of Mg4Ta2O9 ceramics from 1425xa0°C to below 1325xa0°C. The XRD patterns exhibited that chemical reactions happened between Mg4Ta2O9 and B2O3 forming two new phases MgTa2O6 and Mg5TaO3 (BO3)3 during sintering in the materials. As B2O3 additive increased from 0 to 5xa0wt%, MgTa2O6 and Mg5TaO3 (BO3)3 phases also gradually increased. At the same time, the relative permittivity (εr) increased from 11.67 to 12.57, whereas the quality factor (Qf) decreased from 280,000xa0GHz to 170,000xa0GHz, and the temperature coefficient of resonant frequency (τf) remained unchanged. The changes of the dielectric properties with the B2O3 additive content were correlated with the phase evolutions of the material during sintering. Typically, the Mg4Ta2O9-1xa0wt% B2O3 ceramic sintered at 1325xa0°C for 4xa0h acquired the best dielectric properties: εru2009=u200912.15,Qfu2009=u2009260000 GHz,and τf = −u200964xa0ppm/°C.

Low loss and temperature stable microwave dielectric ceramics in (1 − x)Li 2 TiO 3 –xLi 2 Mg 3 TiO 6 (0.1 ≤ x ≤ 0.5) system

The (1u2009−u2009x)Li2TiO3–xLi2Mg3TiO6 (xu2009=u20090.1, 0.15, 0.2, 0.3, 0.4, 0.5) ceramics system was fabricated by solid-state synthesis. Test results of X-ray diffraction and electron diffraction spectrum show that all ceramic samples only contain Li2TO3 and Li2Mg3TiO6 phase. Scanning electron microscope shows that pores were found in crystal grain due to Li volatilization in high temperature (>u20091000xa0°C). With the rise proportion of Li2Mg3TiO6 in ceramics, dielectric constant (ɛr) decreases from 19.55 to 14.53, quality factor (Q×f) increases from 102,800 to 126,000xa0GHz and temperature coefficient (τf) decreases from +u200915.9 to −u200930.08xa0ppm/°C. High performance microwave dielectric properties of ɛru2009=u200918.5, Q×fu2009=u2009108,000xa0GHz, τfu2009=u20094.2xa0ppm/°C were obtained at 1390xa0°C for 0.85Li2TiO3–0.15Li2Mg3TiO6 ceramics. To suppress Li volatilization, LiF, a low temperature melting addition, was added to 0.85Li2TiO3–0.15Li2Mg3TiO6 ceramics. LiF effective lowers sintering temperature from 1390 to 1175xa0°C due to LiF liquid-phase sintering and restricts Li evaporation, and a well-developed grain morphology and excellent dielectric properties (ɛru2009=u200918.5, Q×fu2009=u200987,000xa0GHz, τfu2009=u2009−u200918xa0ppm/°C) was obtained which hold promise in 4G tele-communication applications.

Temperature stable microwave dielectric ceramics in Li2ZnTi3O8–based composite for LTCC applications

A temperature stable low temperature co-fired ceramic (LTCC) was fabricated by the powder mixture of Li2ZnTi3O8 ceramic, TiO2 τf-tailoring dopant and B2O3–La2O3–MgO–TiO2 (BLMT) glass sintering aid, and the sintering behavior, activation energy, phase composition, microstructure and microwave dielectric properties of the composite were investigated in the composition range (wt%) of 5 BLMT–(95-x) Li2ZnTi3O8−X TiO2 (xu2009=u20090, 1, 2, 3, 4 and 5). The sintering behavior results showed that all composites could be well sintered at 910xa0°C for 2xa0h through liquid-phase sintering. The activation energy of Li2ZnTi3O8 ceramic was calculated to be 520.9u2009±u200940.46xa0kJ/mol, while 5BLMT–93Li2ZnTi3O8–2TiO2 (in wt%) composite was reduced to 330.98u2009±u200947.34xa0kJ/mol. The XRD results showed that Li2ZnTi3O8 and TiO2 phase stably existed in all sample and a new phase LaBO3 was crystallized from BLMT glass during sintering process. As x increases, the rutile TiO2 phase increased in composite, which could adjust the temperature coefficient of resonant frequency (τf) to near-zero owing to the opposite τf value to other phases. And simultaneously dielectric constant (εr) demonstrated gradually increase, whereas the quality factor (Qu2009×u2009f) decreased gradually. The composite with xu2009=u20092 had an optimal microwave dielectric properties with εru2009=u200925.3, Qu2009×u2009fxa0=xa032,800xa0GHz, and τfxa0=xa0−xa00.54xa0ppm/°C. The corresponding fitting equations of εr, Qu2009×u2009f and τf on the x value were obtained by the Origin software, indicating that the dielectric properties of the composite could be precisely controlled by varying the content of TiO2. In addition, the good chemical compatibility of this material with Ag electrode made it as a potential candidate for LTCC technology.