Low-temperature sintering and microwave dielectric properties of Mg4Nb2O9 ceramics

The effects of V₂O₅ and Li₂CO₃ on the sinterability and microwave dielectric properties of Mg₄Nb₂O₉ (MN) ceramics were investigated. With addition of 1.5wt% V₂O₅, the dielectric constant (?) and Q·? value of MN ceramics sintered at 1,000 °C are comparable to those of pure MN sintered at 1,400 °C. The good results are because of the enhancement of the density by liquid sintering at the lower temperatures. With the mixtures of V₂O₅ and Li₂CO₃, the sintering temperature of MN was further reduced to 925 °C at the expense of the quality factor (Q·?) value. Typically, ? of 13.7 and Q·? value of 78,000 GHz were obtained for the specimens with mixtures of 1.5wt% V₂O₅ and 1.5wt% Li₂CO₃ and sintered at 925 °C for 5 h.     

Microwave dielectric properties of low-firing BiNbO4 ceramics with V2O5 substitution

The effect of V₂O₅ substitution on the sintering behavior and the microwave dielectric properties of BiNbO₄ ceramics were studied. The sintering temperatures of Bi(V _x Nb_1?x )O₄ ceramics decrease from 990 to 810°C with x value increasing from 0.002 to 0.064. The size of grains increased with the sintering temperature increasing and decreased with the substitution amount increasing. The dielectric properties are affected by the microstructures very much. The quality factor Q value is from 2500 to 4000 at about frequency?=?5 GHz and reach to the maximum when x?=?0.032. With the different x value, the Q _f values change between 15000 to 20000 GHz; the τ _f values changes between 0 and +20 ppm/°C between temperature range 25～85°C and decreased with the increasing of x value.     

The effect of sintering atmosphere on V2O5 substituted BiNbO4 microwave ceramics

In multiplayer passive devices, low sintering temperature dielectric materials were needed to co-fire with low melting point inner electrode such as copper or silver, a major problem of base metal electrode (BME) was that the devices must be fired under low oxygen partial pressure atmosphere to protect Cu from oxidation. In this paper, dielectric properties of Bi(V_xNb_1?x)O₄ (x?=?0.001, 0.004, 0.008, 0.016, 0.048) microwave ceramics sintered under air and N₂ atmosphere have been investigated. The densification temperature sintered in different atmosphere decreased from 1010 to 830°C with the amount of V₂O₅ increasing from 0.001 to 0.048. Due to the increasing vacancy defects, the density of ceramics sintered in N₂ was smaller than that sintered in air. The ceramics sintered under N₂ have similar dielectric constant, and its Qf values are higher while x?<?0.016.     

The sintering behavior and microwave dielectric properties of Mg4(Nb,Sb)2O9 ceramics

The sintering behavior, microstructure and microwave dielectric properties of Mg₄(Nb_2?x Sb _x )O₉ (0?≤?x?≤?2) solid solutions were investigated systematically by X-ray diffraction(XRD), scanning electron microscopy(SEM) and a network analyzer. The solid solutions of Mg₄(Nb_2?x Sb _x )O₉ was formed with x value being no more than 1.6. The dielectric constant (?) of the sintered ceramics decreased from 13.06 to 6.28 with Sb content x from 0 to 1.6. With a substitution of Sb⁵⁺ for Nb⁵⁺ (0.04?≤?x?≤?0.08), the sintering temperature of Mg₄Nb₂O₉ ceramics was decreased from 1400 to 1300 °C without degradation of the Qf values. The optimum microwave dielectric properties of ??～?12.26, Qf?～?168,450 GHz, and τ _f?～??56.4 ppm/°C were obtained in the composition of Mg₄(Nb_1.6Sb_0.4)O₉ sintered at 1300 °C.     

Sintering and dielectric properties of Al2O3 ceramics doped by TiO2 and CuO

The effects of CuO and TiO₂ additives on the microstructure and microwave dielectric properties of Al₂O₃ ceramics were investigated. Al₂O₃ ceramics with CuO and TiO₂ additions can be well sintered to achieve 93∼98% theoretical densities below 1,360 °C due to Ti₄Cu₂O liquid phase sintering effect. The Qf values decreased with increasing CuO and TiO₂ content, due to the formation of the second phase Ti₄Cu₂O. However, the varying behaviors of the dielectric constant (ɛ _r ) and temperature coefficients (τ _f ) were associated with phase constitutions, as a result of the change of CuO and TiO₂content. The τ _f can be shifted close to 0 ppm/°C by controlling the content of CuO and TiO₂. The specimens with 0.5 wt.% CuO and 7 wt.% TiO₂ sintered at 1,360 °C for 4 h showed ɛ _r of 11.8, Qf value of 30,000 GHz, and τ _f of −7 ppm/°C.     

Microwave dielectric properties of Mg4Nb2O9 ceramics produced by hydrothermal synthesis

Mg₄Nb₂O₉ ceramics have been prepared by a hydrothermal synthesis in order to reduce the sintering temperature. The sintering and microwave dielectric properties of the hydrothermally processed Mg₄Nb₂O₉ were studied under various sintering temperatures ranging from 900 to 1300°C. The highest Q×f _o value of 26,069 GHz was obtained at the sintering temperature of 1300°C and is attributed to the increased density and appropriate grain growth. τ _f value of ?17.1 ppm/°C was improved by the addition of TiO₂ and τ _f value of 6.7 ppm/°C was obtained at 20 wt% TiO₂. Chemical compatibility of Mg₄Nb₂O₉ with Ag was tested to identity the possibility of using Mg₄Nb₂O₉ for an LTCC application. Since any secondary phase was not observed in the XRD pattern of the mixtures of Mg₄Nb₂O₉ and Ag powder heat treated at 900°C, it was considered that the Mg₄Nb₂O₉ system is applicable to the multilayer microwave devices using Ag as an electrode.     

Effect of B2O3 and CuO on the sintering temperature and microwave dielectric properties of the BaTi4O9 ceramics

The effect of B₂O₃ and CuO on the sintering temperature and microwave dielectric properties of BaTi₄O₉ ceramics was investigated. The BaTi₄O₉ ceramics were able to be sintered at 975^∘C when B₂O₃ was added. This decrease in the sintering temperature of the BaTi₄O₉ ceramics upon the addition of B₂O₃ is attributed to the formation of BaB₂O₄ second phase whose melting temperature is around 900^∘C. The B₂O₃ added BaTi₄O₉ ceramics alone were not sintered below 975^∘C, but were sintered at 875^∘C when CuO was added. The formation of BaCu(B₂O₅) second phase could be responsible for the decrease in the sintering temperature of the CuO and B₂O₃ added BaTi₄O₉ ceramics. The BaTi₄O₉ ceramics containing 2.0 mol% B₂O₃ and 5.0 mol% CuO sintered at 900^∘C for 2 h have good microwave dielectric properties of ε_r = 36.3, Q× f = 30,500 GHz and τ_f = 28.1 ppm/^∘C     

Effects of V2O5 addition on the phase-structure and dielectric properties of zinc titanate ceramics

V₂O₅-doped zinc titanate ceramics (ZnTiO₃) were prepared by conventional mixed-oxide method combined with a semi-chemical processing. The effects of V₂O₅ addition on the phase-structures and the dielectric properties of ZnTiO₃ ceramics were investigated. The results show the sintering temperature of zinc titanate ceramics could be lowered from 1,150 to 930 °C by reducing the size of starting powders using a semi-chemical processing; and with adding V₂O₅ addition, the densification temperature of ZnTiO₃ ceramics could be reduced to 875 °C. Also the phase transition temperature from hexagonal ZnTiO₃ phase to cubic Zn₂TiO₄ was lowered by adding V₂O₅. The best properties were: ? _r?=?20.6, $ Q \times f = 8,873\;{\text{GHz}} $ , when the ceramics was sintered at 900 °C, which is a promising candidate in the field of multi-layer devices requiring low sintering temperature (≤900 °C).     

Improved giant dielectric properties in microwave flash combustion derived and microwave sintered CaCu 3 Ti 4 O 12 ceramics

The nanocrystals of CaCu3Ti4O12 ceramic were prepared by microwave flash combustion technique. The microwave sintering of powders was optimized to 1025 − 1075 °C for 20 min with heating and cooling rate of 50 °C/min. Microstructural evaluation of sintered sample was carried out using SEM. The dielectric properties were measured in the frequency range 10–2 × 106 Hz and the temperature range 30–100 °C. The CCTO sample sintered at 1075 °C had giant dielectric constant 53,300 at 100 Hz. It was observed that dielectric constant was greatly increased on a slight increase in sintering temperature. Modulus and impedance analysis were performed to explore the observed unusual dielectric response. Grain and grain boundary resistance were observed as 8 Ω and 350,000 Ω, respectively. The grain boundary activation energy for electro-conduction was calculated as 0.65 eV by using the characteristic frequencies in cole-cole plots. It was noticed that the thermally activated charge carriers had long-range mobility.     

Structural and microwave dielectric properties of Ba5-xLaxTixNb4-xO15 ceramics

The structural and microwave dielectric properties of Ba_5?x La _x Ti _x Nb_4?x O₁₅ (1?≤?x?≤?3) was investigated. The single phase with A₅B₄O₁₅-type cation-deficient hexagonal perovskite structure was obtained over the whole composition range. These ceramics have high dielectric constant up to 56, high quality factors (Q?×?f ) up to 35,000, and low temperature coefficient of resonant frequencies (τ _f ) in the range +69 to ?3 ppm °C^?1. The dielectric constants and τ _f of these ceramics gradually decrease parallel to an increase in B-site bond valence with increasing La and Ti content.     

Phase transformation and microwave dielectric properties of BiPO4 ceramics

Monazite-type compounds, BiPO₄ polymorphs were prepared by the solid-state reaction method. The phase transformation and microwave dielectric properties of sintered ceramics were investigated using the X-ray powder diffraction (XRD) and a network analyzer, respectively. The low-temperature phase of BiPO₄ has monoclinic structure, and was transformed into the high-temperature phase with a slight distortion of monoclinic when it is heated above 600^∘C. The effect of the transformation on the microwave dielectric properties was examined. It was found that the dielectric properties of each phase were significantly different. In particular, the high-temperature phase sintered at 950^∘C has good microwave dielectric properties; the relative dielectric constant (ε _r ) = 22, the quality factor (Q× f) = 32,500 GHz and the temperature coefficient of resonant frequency (τ _f ) = − 79 ppm/ ^∘C.     

Effects of BaWO4 and MnWO4 on the microwave dielectric properties of (Zr0.8 Sn0.2)TiO4 ceramics

Abstract

The effects of BaWO₄ and MnWO₄ on the microwave dielectric properties for (Zr_0.8Sn_0.2)TiO₄ ceramics have been investigated as a function of additives concentrations (0–5 mol%). As the amount of BaWO₄ and MnWO₄ increase up to 1 mol%, the unloaded Q increases due to reduction of the oxygen vacancy concentration. Further addition of BaWO₄ or MnWO₄ causes the unloaded Q to decrease due to the presence of secondary phases, either BaWO₄ itself or a needle shaped undetermined MnWO₄ phase. The temperature coefficient of resonant frequency can be controlled by the volume mixing rule for (Zr_0.8Sn_0.2)TiO₄ and secondary phases.     

Effect of La3+ substitution on microwave dielectric properties of (Pb0.5Ca0.5)(Fe0.5Nb0.5)O3 ceramics

Microwave dielectric properties of the [(Pb_0.5Ca_0.5)_1?x La_2x/3](Fe_0.5Nb_0.5)O₃ and [(Pb_0.5Ca_0.5)_1?x La _x ](Fe_0.5Nb_0.5)O₃ ceramics were investigated as a function of La³⁺ content $ {\left( {0.0 \leqslant \times \leqslant 0.2} \right)} $ . A single perovskite phase was detected in [(Pb_0.5Ca_0.5)_1?x La_2x/3](Fe_0.5Nb_0.5)O₃, while Pb₃Nb₄O₁₃ were detected as a secondary phase in [(Pb_0.5Ca_0.5)_1?x La _x ](Fe_0.5Nb_0.5)O₃ beyond x?=?0.05 due to the excess of unbalanced charge. The amount of Pb₃Nb₄O₁₃ was proportional to the unbalanced charge. Qf value of [(Pb_0.5Ca_0.5)_1?x La_2x/3](Fe_0.5Nb_0.5)O₃ decreased remarkably with La³⁺ substitution due to the increase of oxygen vacancy. For [(Pb_0.5Ca_0.5)_1?x La _x ](Fe_0.5Nb_0.5)O₃ ceramics, dielectric constant and Qf value increased with La³⁺ content up to x?=?0.03 due to an increase of density and grain size. Temperature coefficient of resonant frequency (TCF) was depended on B-site bond valence in single perovskite phase.     

Sintering and dielectric properties of (Ta2O5)1−x (TiO2) x polycrystalline ceramics

(Ta₂O₅)_1?x (TiO₂) _x system ceramics has been studied intensively as a promising dielectric material for next generation of high density dynamic random access memories instead of SiO₂ and Si₃N₄. It is found that the dielectric permittivity of (Ta₂O₅)_1?x (TiO₂) _x ceramics was dependent of fabrication process. But in the previous work, their calcining and sintering time were too long, generally for 24 h or even more. A relatively quick sintering process was provided which calcining and sintering time can be decreased to 12 h at 1200°C and 1 h at 1550°C, respectively. This kind of sintering process can save a lot of energy and time that is in favor of the industrial production. Under this sintering process, the composition dependent dielectric properties of (Ta₂O₅)_1?x (TiO₂) _x ceramics have been studied in a wide range of composition (0.01?≤?x?≤?0.20), and the dielectric constants of most compositions can be drastically enhanced. The maximum dielectric value can reach 216 at composition x?=?0.04. In the meantime, the mechanism of improvement of ceramic dielectric constants sintered at 1550°C was also discussed.     

Microwave dielectric properties of B2O3-added Li2MgTiO4 ceramics for LTCC applications

Li₂MgTiO₄ (LMT) ceramics which are synthesized using a conventional solid-state reaction route. The LMT ceramic sintered at 1250°C for 4 h had good microwave dielectric properties. However, this sintering temperature is too high to meet the requirement of low-temperature co-fired ceramics (LTCC). In this study, the effects of B₂O₃ additives and sintering temperature on the microstructure and microwave dielectric properties of LMT ceramics were investigated. The B₂O₃ additive forms a liquid phase during sintering, which decreases the sintering temperature from 1250°C to 925°C. The LMT ceramic with 8 wt% B₂O₃ sintered at 925°C for 4 h was found to exhibit optimum microwave dielectric properties: dielectric constant 15.16, quality factor 64,164 GHz, and temperature coefficient of resonant frequency -28.07 ppm/°C. Moreover, co-firing of the LMT ceramic with 8 wt% B₂O₃ and 20 wt% Ag powder demonstrated good chemical compatibility. Therefore, the LMT ceramics with 8 wt% B₂O₃ sintered at 925°C for 4 h is suitable for LTCC applications.     

Control of 0.2CaTiO3-0.8Li0.5Nd0.5TiO3 microwave dielectric ceramics by additions of Bi2Ti2O7

Ceramics of 0.2CaTiO₃-0.8Li_0.5Nd_0.5TiO₃) have been prepared by the mixed oxide route using additions of Bi₂O₃-2TiO₂ (up to 15 wt%). Powders were calcined 1100^∘C; cylindrical specimens were fired at temperatures in the range 1250–1325^∘C. Sintered products were typically 95% dense. The microstructures were dominated by angular grains 1–2 μm in size. With increasing levels of Bi₂O₃-2TiO₂ additions, needle and lath shaped second phases developed. For Bi₂Ti₂O₇ additions up to 5 wt%, the relative permittivity increased from 95 to 131, the product of dielectric Q value and measurement frequency increased from 2150 to 2450 GHz and the temperature coefficient of resonant frequency (τ _f ) increased from −28pp/^∘C to +22pp/^∘C. A product with temperature stable τ _f could be obtained at ∼2 wt% Bi₂Ti₂O₇ additions. For high levels of additives, there is minimal change in relative permittivity, the Qxf values degrade and τ _f becomes increasingly negative.     

Phase formation,microstructure and microwave dielectric properties of Li2SnO3-MO (M=Mg,Zn,) ceramics

Phase formation, microstructure and microwave dielectric properties of (1-x)Li₂SnO₃-xMO (M=Mg, Zn) ceramics have been investigated using x-ray powder diffractometer (XRD), scanning electron microscope (SEM) and a network analyzer at the frequency of about 8-12GHz in this paper. The results showed that Li₂SnO₃ formed limited range of solid solution ((β-Li₂SnO₃(ss)) with MgO doping (x?≤?0.1) or ZnO doping (x?≤?0.3). Multiphase of Li₄MgSn₂O₇, β-Li₂SnO₃ (ss) and α-Li₂SnO₃(ss) existed in the compositions of x?=?0.2?0.5 for MgO-added specimens. ZnO second phase appeared when x?>?0.3 for the ZnO–added specimens. Dense and homogeneous microstructure could be obtained for the ZnO-doped composition with x?=?0.3. The dielectric permittivity decreased with the increase of MgO doping content, but increased with the increase of ZnO dopant within the miscible compositional range (β-Li₂SnO₃(ss)). The presence of Li₄MgSn₂O₇ or ZnO second phase reduced the dielectric permittivity. The doping of ZnO improved the Q?×?f value of β-Li₂SnO₃(ss), whereas the doping of MgO slightly decreased the Q?×?f value. The improvement of Q?×?f value could be ascribed to the stabilization of the ordering-induced domain boundaries by the partial segregation of the larger doping cation. The τ _f value changed from positive into negative value with increasing MgO or ZnO addition and near zero τ _f value (4.67 or ?0.27 ppm/°C) could be obtained at x?=?0.3 composition for MgO or ZnO added specimens, respectively.     

Preparation and dielectric properties of La doped NBCCTO ceramics

Journal of Electroceramics - CaCu3Ti4O12 ceramics have great dielectric constant, excellent temperature stability and good frequency stability. However, due to high dielectric loss, its practical...     

Effect of B2O3 addition on the microwave dielectric properties of Li2ZnTi3O8 ceramic

Li₂ZnTi₃O₈ ceramics doped with B₂O₃ were prepared by the conventional solid-state reaction. The effects of B₂O₃ additions on the sintering characteristic, phase composition, microstructure and microwave dielectric properties of Li₂ZnTi₃O₈ ceramics were investigated. The addition of B₂O₃ reduces the sintering temperature of the Li₂ZnTi₃O₈ ceramic from 1075 °C to 925 °C. Only a single phase Li₂ZnTi₃O₈ forms in the Li₂ZnTi₃O₈ ceramic with less than 2.0 wt% B₂O₃ sintered at 925 °C. However, when the addition of B₂O₃ exceeds 2.0 wt%, the second phase Li₂B₄O₇ appears in the Li₂ZnTi₃O₈ ceramic. Li₂ZnTi₃O₈ ceramic doped with 1.5 wt% B₂O₃ addition sintered at 925 °C reaches a maximum relative density of 94.5 % and exhibits good microwave dielectric properties of ε_r?=?24.96, Q×f?=?49,600 GHz and τ_f?=??11.3 ppm/°C.