Improved Microwave Dielectric Properties Research Articles

Novel Series of Low‐Firing Microwave Dielectric Ceramics: (1−x)Li3Bi2P3O12–xTiO2

A new thermally stable microwave dielectric ceramic with low‐firing temperature in (1−x)Li3Bi2P3O12–xTiO2 [(1−x)LBP–xT, 0 ≤ x ≤ 0.6] ceramics system was obtained using conventional solid‐state reaction method. The phase transformation, microstructure, and microwave dielectric properties of materials were investigated using X‐ray powder diffraction (XRD), scanning electron microscopy (SEM) , and a network analyzer. The LBP ceramic (x = 0) sintered at 725°C has optimum microwave dielectric properties with relative permittivity (εr) of 15.8, Q × f of 26 600 GHz and temperature coefficients of resonant frequency (τf) of −130 ppm/°C. The εr and τf of (1−x)LBP–xT ceramics were tailored with increasing x values. At x = 0.55, the ceramic exhibits improved microwave dielectric properties with εr = 22.1, Q × f = 14 900 GHz and τf = −2.6 ppm/°C.

Improved Microwave Dielectric Properties of La(Mg0.5Sn0.5)O3 Ceramics with Yb3+ Doping

The La1−xYbx(Mg0.5Sn0.5)O3 ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the La0.97Yb0.03(Mg0.5Sn0.5)O3 ceramics revealed no significant variation of phase with sintering temperatures. An apparent density of 6.65 g/cm3, a dielectric constant (er) of 20.2, a quality factor (Q × f) of 56,800 GHz, and a temperature coefficient of resonant frequency (τf) of −76.9 ppm/°C were obtained for La0.97Yb0.03(Mg0.5Sn0.5)O3 ceramics that were sintered at 1550°C for 4 h.

Improved microwave dielectric properties of Nd(Mg0.5Sn0.5)O3 ceramics by substituting Mg2+ with Zn2+

This study elucidates the microwave dielectric properties and microstructures of Nd(Mg0.5−xZnxSn0.5)O3 ceramics for their potential applications in microwave devices. The Nd(Mg0.5−xZnxSn0.5)O3 ceramics were prepared by the conventional solid-state method with various sintering temperatures. X-ray diffraction (XRD) patterns of the Nd(Mg0.4Zn0.1Sn0.5)O3 ceramics revealed only a slight variation of phase with sintering temperatures. Additionally, a dielectric constant (εr) of 19.5, a quality factor (Q×f) of 129,200GHz, and a temperature coefficient of resonant frequency (τf) of −66ppm/°C were obtained for Nd(Mg0.4Zn0.1Sn0.5)O3 ceramics sintered at 1500°C for 4h.

Effects of Al2O3 addition on the sintering behavior and microwave dielectric properties of CaSiO3 ceramics

The effects of Al2O3 addition on the densification, structure and microwave dielectric properties of CaSiO3 ceramics have been investigated. The Al2O3 addition results in the presence of two distinct phases, e.g. Ca2Al2SiO7 and CaAl2Si2O8, which can restrict the growth of CaSiO3 grains by surrounding their boundaries and also improve the bulk density of CaSiO3–Al2O3 ceramics. However, excessive addition (≥2 wt%) of Al2O3 undermines the microwave dielectric properties of the title ceramics since the derived phases of Ca2Al2SiO7 and CaAl2Si2O8 have poor quality factor. The optimum amount of Al2O3 addition is found to be 1 wt%, and the derived CaSiO3–Al2O3 ceramic sintered at 1250 °C presents improved microwave dielectric properties of ɛr = 6.66 and Q × f = 24,626 GHz, which is much better than those of pure CaSiO3 ceramic sintered at 1340 °C (Q × f = 13,109 GHz).

Improved Microwave Dielectric Properties of La(Mg0.5Sn0.5)O3Ceramics with Yb3+Doping

The La1−xYbx(Mg0.5Sn0.5)O3 ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the La0.97Yb0.03(Mg0.5Sn0.5)O3 ceramics revealed no significant variation of phase with sintering temperatures. An apparent density of 6.65 g/cm3, a dielectric constant (εr) of 20.2, a quality factor (Q × f) of 56,800 GHz, and a temperature coefficient of resonant frequency (τf) of −76.9 ppm/°C were obtained for La0.97Yb0.03(Mg0.5Sn0.5)O3 ceramics that were sintered at 1550°C for 4 h.

Influence of lead oxide addition on LnTiTaO6 (Ln = Ce, Pr and Nd) microwave ceramics

The effect of PbO addition on the structural, processing and microwave dielectric properties of LnTiTaO6 (Ln = Ce, Pr and Nd) ceramics are reported. Conventional solid state ceramic route was used for the preparation of samples. Phase pure LnTiTaO6 (Ln = Ce, Pr and Nd) ceramics are prepared at a calcination temperature of 1300°C. The samples are sintered at optimized temperatures. Addition of PbO reduces the sintering temperature. The crystal structure of the materials was analysed using X-ray diffraction techniques and the surface morphology of the sintered samples was analysed using scanning electron microscopy. The dielectric constant at microwave frequency range decreases for higher PbO addition for all the samples but the quality factor improves on small PbO addition. The thermal stability of resonant frequency was also improved with PbO addition on all the systems. A number of samples with improved microwave dielectric properties were obtained on all the systems suitable for practical applications.

Low-Temperature Sintering and Microwave Dielectric Properties of the Zn<sub>2</sub>SiO<sub>4</sub> Ceramics

Willemite ceramics (Zn2SiO4) possess excellent millimeter-wave dielectric properties, but it also has a high sintering temperature above 1300°C by traditional solid-state reaction and relatively large negative τf value. Zn2SiO4 nanoparticles synthesized by Sol–Gel method were used to improve the sintering and dielectric properties of the Zn2SiO4 ceramics. Using the nanoparticles, Zn2SiO4 ceramics can be sintered at a low temperature, 1150°C and exhibited improved microwave dielectric properties of εr =6.62, Q × f=24500 GHz, τf =-59ppm/°C. By adding TiO2 with high positive τf value (+450 ppm/°C) and CuO as sintering aid, near zero τf value and low sintering temperature can be achieved. With 11wt% of TiO2 and 5 wt% of CuO, an εr value of 9.3, a Q × f value of 12200GHz and a τf value of -11 ppm/°C were obtained at 1000°C, confirming the promising potential of the CuO-added TiO2-Zn2SiO4 ceramics as candidate materials for low–temperature cofired ceramic (LTCC) devices.

Effect of WO 3 and MoO 3 addition on LnTiTaO 6 (Ln = Ce, Pr and Nd) microwave ceramics

The effect of dopants such as WO 3 and MoO 3 on the structural, processing and microwave dielectric properties of LnTiTaO 6 (Ln = Ce, Pr and Nd) ceramics is reported. Conventional solid-state ceramic route was used for the preparation of samples. The samples are calcined and sintered at optimized temperatures. A reduction of 50 °C in the sintering temperature was observed for all the samples. The crystal structure of the materials was analyzed using X-ray diffraction techniques and the surface morphology of the sintered samples was analyzed using scanning electron microscopy. The dielectric constant at microwave frequency range decreased on higher doping concentrations for all the samples but the quality factor is improved on small doping concentrations. The thermal stability of resonant frequency is also improved with doping on all the systems. A number of samples with improved microwave dielectric properties were obtained on all the systems and are suitable for practical applications.

Improved Microwave Dielectric Properties of Ba6Ti1−xSnxNb4O18Ceramics

Single-phase polycrystalline microwave dielectric ceramics Ba6Ti1−xSnxNb4O18, with x changing from 0 to 1, were synthesized by the solid-state reaction method. All the solid solutions fitted well with A6B5O18 cation-deficient hexagonal perovskite structure. The substitution of Sn for Ti effectively enhanced the quality factor and controlled τf. With increasing Sn content, the dielectric constant decreased from ∼47 to ∼32, and the Q×f value increased significantly from 11 530 to 28 496 GHz, with τf varying from 64 to 0 ppm/°C. A zero τf was realized when Sn was fully replaced by Ti with the composition Ba6SnNb4O18.

Effect of Zn/Si Ratio on the Microstructural and Microwave Dielectric Properties of Zn2SiO4 Ceramics

Zn2SiO4 ceramics synthesized by the conventional solid‐state method exhibited a low Q×f value, possibly due to the formation of a ZnO second phase. However, with a small ZnO reduction from the Zn2SiO4 ceramics, the ZnO second phase disappeared and grain growth occurred due to the formation of a Si‐rich liquid phase. Specimens with a large grain size exhibited an improved Q×f value. In particular, the ceramics with nominal composition Zn1.8SiO3.8 sintered at 1300°C exhibited improved microwave dielectric properties of ɛr=6.6, Q×f=147 000 GHz, and τf=−22 ppm/°C.

Improved microwave dielectric properties of B 2O 3-doped Nd(Co 1/2Ti 1/2)O 3 ceramics with near zero temperature coefficient of resonant frequency

The microwave dielectric properties and the microstructures of Nd(Co 1/2Ti 1/2)O 3 ceramics prepared by conventional solid-state route have been studied. The prepared Nd(Co 1/2Ti 1/2)O 3 exhibited a mixture of Co and Ti showing 1:1 order in the B-site. It is found that low-level doping of B 2O 3 (up to 0.75 wt.%) can significantly improve the density and dielectric properties of Nd(Co 1/2Ti 1/2)O 3 ceramics. Nd(Co 1/2Ti 1/2)O 3 ceramics with additives could be sintered to a theoretical density higher than 98.5% at 1320 °C. Second phases were not observed at the level of 0.25–0.75 wt.% B 2O 3 addition. The temperature coefficient of resonant frequency ( τ f ) was not significantly affected, while the dielectric constants ( ɛ r) and the unloaded quality factors Q were effectively promoted by B 2O 3 addition. At 1320 °C/4 h, Nd(Co 1/2Ti 1/2)O 3 ceramics with 0.75 wt.% B 2O 3 addition possesses a dielectric constant ( ɛ r) of 27.2, a Q × f value of 153,000 GHz (at 9 GHz) and a temperature coefficient of resonant frequency ( τ f ) of 0 ppm/°C. The B 2O 3-doped Nd(Co 1/2Ti 1/2)O 3 ceramics can find applications in microwave devices requiring low sintering temperature.

Improved microwave dielectric properties of (Mg1−(x+y)CaxLay)(Ti1−yAly)O3 ceramics

Phase-singular solids of the composition, (Mg1−(x+y) Cax Lay)(Ti1−yAly)O3 (x=0 to 0.88; y=0.05 to 0.35) having the cubic perovskite-type structure were prepared by the substitution of La3+ and Al3+ in equivalent quantities which brought about complete miscibility between MgTiO3 and CaTiO3. These ceramics showed relative permittivities of 16.5 to 50 (at 6GHz) with increasing Ca content, high Q values of 10 000 to 30 000 and retained near-zero temperature coefficients in permittivity at optimum y values. Their dielectric characteristics are better accountable in terms of the positional disorder rather than the tolerance factor of perovskite structure.

Low Loss Tunable Thick Films Based on (Ba,Sr)TiO3 and Ba4Ti13O30 Materials

Modification on microwave dielectric properties of (Ba0.6Sr0.4)TiO3 (BST) materials due to the incorporation of Ba4Ti13O30 (B4T13) materials was investigated. The dielectric constant of the BST materials was lowered from KBST = 600 to KCOMP = 100, whereas the quality factor of the materials was increased markedly from (Q ×} f)BST = 80 to (Q ×} f)COMP = 2,000, due to the addition of B4T13 materials. Evanescent microwave probe (EMP) measurements indicate that the thick films prepared from the mixture contain two phases. The low-K and high-Q particulates, which are presumably B4T13 phase, are distributed uniformly among the high-K and low-Q matrix, resulting in a tunable materials with improved microwave dielectric properties.

Mo을 치환한 BiNbO4세라믹 후막 모노폴 안테나의 전기적 특성

We fabricated thick film monopole antennas using Mo-doped BiNbO<TEX>$_4$</TEX> ceramics and investigated their electrical properties as a function of the Mo-doping concentration. Compared with undoped BiNbO<TEX>$_4$</TEX> ceramics, 10 at.% Mo-doping improved microwave dielectric properties of ceramics by increased sintered density as well as decreased space charge density. Further increase in the Mo-doping concentration caused formation of Bi<TEX>$_2$</TEX>MoO<TEX>$_{6}$</TEX> phases, resulting in deterioration of the microwave characteristics. The gain and bandwidth of the ceramic monopole antenna were also greatly affected by the Mo-doping concentration. When Mo-doping concentration was 10 at.%, highest gain of -0.7dBi with lowest bandwidth of 30% at 2.3GHz was obtained.

Microwave dielectric materials based on the MgO–SiO2–TiO2 system

Abstract Ceramics in the system MgO–SiO 2 –TiO 2 were prepared by standard mixed oxide route. By adding ZnO–B 2 O 3 to the starting mixtures, the firing temperature of the ceramics could be reduced to 1160 °C. Small additions of MnCO 3 and CaTiO 3 improve microwave dielectric properties leading to an increase in insulation resistance and a decrease in temperature coefficient of capacitance. By adding Co 2 O 3 grain growth can be inhibited and the dielectric Qf value greatly increased. The resultant ceramic material exhibited low dielectric constant and low dielectric loss: relative permittivity ( e r ): 20±2; temperature coefficient of capacitance ( τ c ): 0±30 ppm/°C; Qf : 100,000 (at 10 GHz); insulation resistance: 10 13 Ω cm:

Microwave Dielectric Properties of Y2Ba(Cu1-xZnx)O5 Solid Solutions

The microwave dielectric properties of Y2Ba(Cu1-xZnx)O5 (0≤x≤1) solid solutions, prepared by the solid state reaction method, were studied in relation to the amount of Zn substitutions, and measured using the Hakki and Coleman method. The εr and the τf increased slightly, and the Q·f values changed nonlinearly as the amount of Zn substitution was increased. In particular, it is shown that improved microwave dielectric properties with Q·f=110665 GHz, εr=14.2 and τf=-41.5 ppm/°C are obtained for samples with x=0.5, which also have few pores and high relative density. Thus, it was concluded that the Q·f values were closely related to the presence of pores in the samples.