Microwave Dielectric Properties Of Ceramics Research Articles

Effects of lithium fluoride addition on sintering characteristics and microwave dielectric properties of rock–salt structure Li2Mg4TiO7 ceramics

Li2Mg4TiO7 ceramics doped with 1–5 wt% LiF were successfully prepared by the conventional solid-state method. The sintered samples could be well indexed as the rock salt structure with space group Fm-3m (JCPDS #70-2711). The sintering behaviors, phase compositions, microstructures and microwave dielectric properties of ceramics were associated with the sintering temperature and the amount of LiF addition. The e r and Q·f values of the Li2Mg4TiO7 ceramics increased firstly and then decreased with increasing the amount of LiF addition. A near zero temperature coefficient of resonant of frequency (τ f ) value could be obtained by adjusting the amount of LiF additions. The Li2Mg4TiO7 ceramics doped with 2 wt% LiF sintered at 950 °C for 4 h possessed promising microwave dielectric properties with e r value of 14.43, Q·f value of 48,700 GHz and τ f value of −3.83 ppm/°C, making them suitable for low-temperature co-fired ceramic applications.

Phase evolution, microstructure and microwave dielectric properties of 2Li2O-AO-3WO3 (A=Mg, Zn) composite ceramics

Low-firing microwave dielectric ceramics with compositions of 2Li2O-AO-3WO3 (A=Mg, Zn) were prepared by the solid state reaction method. The sintering behavior, microstructure and microwave dielectric properties of ceramics were investigated. The bulk density, quality factor (Q × f) and relative permittivity (e r ) of 2Li2O-AO-3WO3 (A=Mg, Zn) ceramics firstly increased, reached a max value and then decreased with increasing the sintering temperature. 2Li2O-MgO-3WO3 ceramics shown a low sintering temperature (~700 °C) and good microwave dielectric properties with Q × f value of 23,582 GHz, e r of 5.89 and τ f value of −78 ppm/°C. 2Li2O-ZnO-3WO3 ceramics sintered at 675 °C also presented excellent microwave dielectric properties with Q × f = 21,706 GHz, e r = 6.76 and τ f = −94 ppm/°C. Most importantly, 2Li2O-AO-3WO3 (A=Mg, Zn) ceramics illustrated good chemical compatiblity with silver powders, which indicate that they can be used to LTCC multilayer devices.

Compatibility with silver electrode and microwave dielectric properties of low firing CaWO4-2Li2WO4 ceramics

A low firing microwave dielectric ceramic with the composition of CaWO4-2Li2WO4 was prepared by the solid-state reaction method. The phase composition, microstructure and microwave dielectric properties of ceramics were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and network analyzer. The CaWO4-2Li2WO4 ceramics sintered at 740°C for 4h possessed the superior comprehensive performance with relative permittivity (εr) of 6.10, quality factor (Q×f) of 62400GHz and temperature coefficient of resonant frequency (τf) of −100.1ppm/°C. The CaWO4-2Li2WO4 dielectric ceramics were chemically compatible with silver (Ag) electrode, indicating that CaWO4-2Li2WO4 ceramics might be a promising candidate for low temperature co-fired ceramic (LTCC) devices.

Sintering behavior, phase structure and adjustable microwave dielectric properties of Li2O–MgO–nTiO2 ceramics (1 ≤ n ≤ 5)

Li2O–MgO–nTiO2 (1 ≤ n ≤ 5) ceramics were prepared by a solid state reaction method. The sintering behavior, phase evolution, microstructure and microwave dielectric properties of ceramics were investigated. With increasing n value, the microstructure of ceramics changed from a porous structure to the compact structure. Bulk density, relative permittivity (er) and temperature coefficient of resonator frequency (τf) firstly increased, reached a max value and then decreased with increasing n values. Q × f value first decreased, then increased and finally decreased again. When n = 2, Li2O–MgO–2TiO2 systems presented good microwave dielectric properties with Q × f value of 44,914 GHz, er of 20.8 and τf of −10.15 ppm/oC and low density of 3.33 g/cm3. When n = 3, Li2O–MgO–3TiO2 systems showed better comprehensive performances with sintering temperature of 1050 °C, Q × f value of 48,513 GHz, er of 25.5, τf of 1.6 ppm/oC and low density of 3.40 g/cm3.

Phase structure, sintering behavior and adjustable microwave dielectric properties of Mg1−xLi2xTixO1+2x solid solution ceramics

Mg1−xLi2xTixO1+2x (1/5 ≤ x ≤ 1/2) solid solution ceramics were prepared by the solid state reaction method. The sintering behavior, microstructure and microwave dielectric properties of ceramics were investigated. X-ray diffraction patterns showed that MgO and Li2TiO3 could form Mg1−xLi2xTixO1+2x solid solutions with a rock salt structure. With increasing x values, the unit cell parameters of ceramics decreased, both the Q×f value and bulk density increased firstly, reached the max value and then decreased. Most importantly, the thermal stability of microwave dielectric properties for ceramics was improved. When x = 1/4, Li2Mg3TiO6 ceramics exhibited good microwave dielectric properties with Q×f = 110,703 GHz, εr = 13.6 and τf = −35.1 ppm/°C.

Preparation, structure and microwave dielectric properties of 3MgO–Al2O3–3TiO2 ceramics

3MgO–Al2O3–3TiO2 (MAT) ceramics were prepared by a conventional solid-state reaction method. The crystal structure, sintering behavior and microwave dielectric properties of ceramics were investigated using X-ray diffraction, scanning electron microscopy and network analyzer. MAT ceramics contained the coexistence of three phases, including MgAl2O4, MgTiO3 and MgTi2O5. The ceramics sintered at 1350 °C for 4 h presented excellent comprehensive performances with relative permittivity (e r ) of 15.4, quality factor (Q × f) of 91,000 GHz and temperature coefficient of resonant frequency (τ f ) about −55.1 ppm/°C.

Structure and microwave dielectric properties of ZnTa2O6 ceramics with TiO2 and ZrO2 additions

Ceramic samples based on ZnTa2O6 and ZnTa2O6–MO2 (M = Ti, Zr) systems have been obtained by the solid state ceramic route. The phase composition and microstructure of samples were investigated. The effect of the aliovalent substitution of ions Zn2+ and Ta5+ by M4+ (M = Ti, Zr) in the structure of ZnTa2O6 on microwave dielectric properties of ceramics was studied. The way of the compensation of the positive temperature coefficient of resonant frequency of dielectric resonators based on ZnTa2O6 ceramics with using the aliovalent substitution of cations was proposed. Dielectric resonators with the high temperature stability of the resonant frequency and high dielectric properties in the microwave range based on the ZnTa2O6–ZrO2 system were obtained for application in electronics.

Characterization and Microwave Dielectric Properties of Mg4Nb2O9 ceramics produced via using nanopowders

ABSTRACTMg4Nb2O9 ceramics were prepared by using nanopowders (average grain size of 63.4 nm) as a precursor, synthesized via high-energy ball milling method at 900°C. The microstructure, sintering behaviors and microwave dielectric properties of ceramics are systematically investigated. Due to the refined grains, Sintering temperature of Mg4Nb2O9 ceramics is effectively reduced to 1200°C, 150°C lower than that required by a conventional solid state reaction process. Mg4Nb2O9 ceramics possess a relative densities of 96.4%, a grain size of 1.5–5.0 μm and an excellent microwave dielectric properties (ϵr of 12.6, Q ×f of 175810.0 GHz, and τf of −56.6 ppm/°C), which make it as a potential candidate for practical application.

Optimized sintering temperature and enhanced microwave dielectric performance of Mg2B2O5 ceramic

Mg2B2O5 ceramic was prepared by a solid-state reaction process using the mole ratio of MgO:B2O3 = 1:1. The crystal structure, sintering behavior and microwave dielectric properties of ceramics were investigated by X-ray diffraction, scanning electron microscopy and dielectric measurement. The Mg2B2O5 ceramic can be well densified at 1100 °C for 4 h. X-ray diffraction patterns show that the ceramic is a pure Mg2B2O5 (P-1) anorthic phase structure with parameters of a = 6.1563(1) A, b = 9.2228(1) A, c = 3.1217(1) A, α = 90.4618(2)°, β = 92.1601 (1)°, γ = 104.3993(1)°, V = 171.53(1) A3. The best microwave dielectric properties can be obtained in ceramic sintered at 1100 °C for 4 h with permittivity about 5.83, Q × f about 41,930 GHz and τ f about −62 ppm/°C.

A novel self-composite property-tunable LaTiNbO6 microwave dielectric ceramic

A novel self-composite LaTiNbO6 microwave dielectric ceramic was fabricated via a solid-state reaction method together with an annealing process. A monoclinic LaTiNbO6 after a conventional sintering was found to gradually transform into an orthorhombic counterpart with prolonging annealing time. Microwave dielectric properties of ceramics can be easily tailored by changing the relative content of two coexisting phases with complementary performances. A thermal-stable dielectric ceramic (εr=30.2, Qÿf=GHz) was yielded after annealing at 1100°C for 1h. The concept of the self composite might provide an innovative and simple way to develop property-tunable microwave dielectric ceramics.

Microwave dielectric properties of sol-gel derived CoTiNb2O8 ceramics

CoTiNb2O8 microwave dielectric ceramics were synthesized via a modified sol-gel route. The thermal decomposition behavior of the as-prepared precursor was characterized by differential thermal analysis (DTA)/thermogravimetry (TG). Highly reactive CoTiNb2O8 nano-powders with average particle size of 34 nm were achieved by the reaction between TiO2 and intermediate phase CoNb2O6 at 800 °C. The microwave dielectric properties of ceramics were sensitive to processing condition and crystal structure. For the CoTiNb2O8 compounds, the variations of εr and Q × f value agreed well with that of the relative density. The τf was explained in terms of oxygen octahedral distortion and B-site bond valence. At 1000°C/4h, CoTiNb2O8 ceramic possessed optimal microwave dielectric properties with an εr of 64.19, a high Q × f of 16,800 GHz (at 6.4 GHz) and a τf of 66.17 ppm/°C.

Investigation of the microwave dielectric properties of Li2ZnTi5O12 ceramics

Cubic-structured Li2ZnTi5O12 ceramics were prepared by a conventional solid-state reaction method, and their characterization and microstructure were investigated, with the microwave dielectric properties of these ceramics being studied for the first time. The relationships between the sintering temperature and the microwave dielectric properties in Li2ZnTi5O12 ceramics were also studied. The variation trend of the dielectric constant was in accordance with that of the apparent density. The Q × f and τf were correlated with the density (an extrinsic factor), FWHM (an intrinsic factor) and bond valence in these compositions, respectively. The new microwave dielectric material Li2ZnTi5O12 ceramics sintered at 1260 °C for 4 h have a dielectric constant (εr) of ∼38.4, a Q × f of ∼54,300 GHz (f = 5.898 GHz), and a τf ∼ 82.9 ppm/°C, and thus they are a suitable candidate for use in microwave applications.

New microwave dielectric system of Li4x Mg3(1−x)Al6(1−x)Ti5x O12 with adjustable thermal stability and high quality factor

Li4x Mg3(1−x)Al6(1−x)Ti5x O12 (x = 0.2, 0.4, 0.6, 0.8) ceramics were prepared by a solid state reaction method. The phase evolution, microstructure and composition of ceramics were investigated using X-ray powder diffractometer, scanning electron microscope, energy dispersive spectrometer. The microwave dielectric properties of ceramics were studied by a network analyzer. Both MgAl2O4 and Li4Ti5O12 have a cubic spinel structure, whereas no uniform solid solution was formed in Li4x Mg3(1−x)Al6(1−x)Ti5x O12 ceramics. There were Al-rich compounds and Ti-rich compounds in the mixed phases. With increasing x form 0.2 to 0.8, Al-rich compounds decreased and Ti-rich compounds increased. A complex phase evolution was appeared in the process, such as Mg2TiO4, Li2MgTi3O8 and Li4Ti5O12 compounds. With increasing x values, the sintering temperature was reduced from 1280 to 925 °C. Li4x Mg3(1−x)Al6(1−x)Ti5x O12 ceramics presented an excellent comprehensive performance with e r of 11.5–26.5, Q × f values of 7102–30,191 GHz and τ f values of −55.4 ~ +5.7 ppm/ °C.

Novel middle permittivity ceramic Ba4CoTi11O27: Sintering characteristic, cations distribution, crystal structure and microwave dielectric properties

Novel middle permittivity microwave dielectric ceramic with the composition of Ba4CoTi11O27 was prepared by a solid-state reaction process. The crystal structure, sintering behavior and microwave dielectric properties of ceramics were investigated using X-ray diffraction, scanning electron microscopy and dielectric measurement. The Ba4CoTi11O27 ceramic can be well densified in the temperature range from 1125 to 1275°C. A refinement using X-ray powder diffraction data was carried out in the Rietveld method with the parameters of Ba4Ti12O27 as a starting model. Ba4CoTi11O27 has a monoclinic structure (C2/m) with lattice parameters of a=19.8525(2) Å, b=11.4616(1) Å, c=9.9052(1) Å, β=109.201(2)°, V=2128.49(3) Å3, Z=4 when the sintering temperature is 1225°C. Pure monoclinic Ba4CoTi11O27 ceramic sintered at 1225°C for 3h exhibits excellent microwave dielectric properties with εr=36.5, Q×f=15,290GHz and τf=17.3ppm/°C.

Effect of H<sub>3</sub>BO<sub>3</sub> Additive and Forming Pressure on Microwave Dielectric Properties of 0.95MgTiO<sub>3</sub>-0.05CaTiO<sub>3</sub>

0.95MgTiO3-0.05CaTiO3 (95MCT) microwave dielectric ceramics was prepared solid-state reaction method. Effect of H3BO3 additive and forming pressure on sintering process, microstructure and microwave dielectric properties of 95MCT were investigated. The result showed that the additive of H3BO3 can lower the sintering temperature of 95MCT, and improve the densification of 95MCT. MgTi2O5 was found as mesosphere, which can be effectively suppressed through the additive of H3BO3. Excellent microwave dielectric properties of ceramics was obtained when the H3BO3 additive was 0.50wt%. The best value of dielectric constant (εr), quality factor (Q×f) and temperature coefficient of resonant frequency (τf ) of 21.54, 67,286GHz and-4.1ppm/oC was obtained for the ceramics with sintering 1220oC for 2h.

Sintering characteristic, crystal structure and microwave dielectric properties of a novel thermally stable ultra-low-firing Na2BiMg2V3O12 ceramic

A novel ultra low-firing microwave dielectric ceramic with the composition of Na2BiMg2V3O12 was fabricated by a solid state reaction method. The phase structure, sintering behavior and microwave dielectric properties of ceramics were investigated. The ceramic can be well densified at 660 °C for 4 h. X-ray diffraction data show that Na2BiMg2V3O12 has a cubic garnet structure with lattice parameters of a = 12.4929 A, V = 1,949.80 A3, Z = 8 and ρ = 4.42 g/cm3. The microwave dielectric properties are strongly related to the density and morphology of the samples. The ceramic sintered 660 °C exhibits good microwave dielectric properties with er = 23.2, Q × f = 3,700 GHz and τ f = 8.2 ppm/°C. These results indicate that Na2BiMg2V3O12 ceramic is a candidate for low temperature co-fired ceramics devices, such as chip multi-layer LC filter, microstrip bandpass filter, multilayer antenna.

Series of thermally stable Li1+2x Mg4−x V3O12 ceramics: low temperature sintering characteristic, crystal structure and microwave dielectric properties

Series of novel low-firing microwave dielectric ceramics with the composition of Li1+2x Mg4−x V3O12 (−0.2 ≤ x ≤ 0.1) were prepared by a solid-state reaction process. The crystal structure, sintering behavior and microwave dielectric properties of ceramics were investigated using X-ray diffraction, scanning electron microscopy and dielectric measurement. As x increased from −0.2 to 0.1, the optimized sintering temperature was reduced from 880 to 700 °C, the quality factors (Q × f) were effectively enhanced from 21,000 to 33,200 GHz. A good combined microwave dielectric properties with er = 12.1, Q × f = 21,800 GHz, τ f = 1.8 ppm/°C were obtained for x = −0.1.

Ba4LiNb3−xSbxO12: Phase evolution, microstructure and optimized microwave dielectric properties

Series microwave dielectric ceramics with the composition of Ba4LiNb3−xSbxO12 (0≤x≤3) were prepared by the solid state reaction method. The phase transformation, microstructure and microwave dielectric properties of ceramics were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and a network analyzer. The sequence of structure transformation was detected with increasing x values; Hexagonal (0≤x≤0.75)→Hexagonal+Cubic (0.75<x≤1.25)→Cubic (1.25<x≤3). The microwave dielectric properties were improved through substituting Sb for Nb. Especially, the temperature coefficient of resonate frequency (τf) can be tailored to zero. Based on the overall performance, the best result was obtained for the Ba4LiNb2SbO12 (εr=24.6, Qf=52,100GHz, τf=0ppm/°C), indicating that the Ba4LiNb3−xSbxO12 ceramics are suited for the dielectric resonate applications.

Sintering behavior and microwave dielectric properties of Ca1-xBixW1-xVxO4 ceramics

Structure, sintering behavior and microwave dielectric properties of ceramics have been investigated by x-ray powder diffraction (XRD) and scanning electron microscopy (SEM) in this paper. The microwave dielectric properties of the ceramics were studied with a network analyzer at the frequency of about 6–11GHz. The sintering temperature and microwave dielectric properties could be successfully tuned in a wide window simultaneously by adjusting the A–O bond characteristics. The sintering temperature of CaWO4 was successfully reduced from 1100°C to about 950°C by BiVO4 addition. Approximately 95%–96% theoretical density could be obtained after sintering at 950°C for 2h. All samples exhibit single Scheelite structure (I41/a) phase. The dielectric constant increased, whereas the Q×f value decreased, with the increase of x. The τf value changed from negative to positive with the increases of x. Combined excellent microwave dielectric properties with εr=22. 1, Q×f=16,730GHz and τf=2.39ppm/°C could be obtained after sintered at the 950°C for 2h for x=0.3 compositions.

Sintering Behavior and Microwave Dielectric Properties of MgTiO3 Ceramics Doped with B2O3 by Sol-Gel Method

The B 2 O 3 -doped MgTiO 3 powders and ceramics have been prepared by sol-gel method using Mg(NO 3 ) 2 6H 2 O, Ti(C 4 H 9 O) 4 and H 3 BO 3 as the starting materials. The sintering behavior and microwave dielectric properties of ceramics prepared from powders with different particle sizes were investigated. The gels were calcined at 650, 700, 750, 800, 850 and 900 °C and the derived particle sizes of powders were 20–30 nm, 30–40 nm, 40–60 nm, 60–90 nm, 90–120 nm and 120–150 nm, respectively The nanoparticles with the size of 30–60 nm benefited the sintering process with high surface energy whereas nanoparticles with the size of 20–30 nm damaged the microwave dielectric properties due to the pores in the ceramics. The addition of B 2 O 3 used as a liquid sintering aid reduced the sintering temperature of MgTiO 3 ceramic, which was supposed to enter the MgTiO 3 lattice and resulted in the formation of (MgTi) 2 (BO 3 )O phase. The B 2 O 3 -doped MgTiO 3 ceramic sintered at 1100°C and prepared from the nanoparticles of 40–60 nm had compact structure and exhibited good microwave dielectric properties: ɛ r =17.63, Q × f =33,768 GHz τ f =−48×10 −6 °C −1 .