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1.
Crystallizable zinc borate glasses modified with different contents of La 2O 3 or Nd 2O 3 were investigated as a potential low loss dielectric with respect to their crystallization behavior and microwave dielectric characteristics. The glasses were admixed with Al 2O 3 filler and fired at 850°C for 30 min in air to prepare low temperature dielectrics. Crystallization behavior and microwave dielectric properties of the resulting samples strongly depended on the relative content of La 2O 3 or Nd 2O 3 in the glass. As a promising result, the composition of 0.15ZnO-0.25Nd 2O 3-0.6B 2O 3 exhibited k?~?6.5 and Q?~?1194 at the resonant frequency of 18.9 GHz. Near zero temperature coefficient of frequency (TCF) was obtained by additional modification of the composition with ~10 wt.% of TiO 2 filler. Crystallization kinetics of the samples was studied based on the differential thermal analysis (DTA) curves obtained with different heating rates. Correlation of the observed dielectric properties to the crystallization behavior is the main subject of this work. 相似文献
2.
Though need for precise alignment of interlayer patterning in LTCC application, there have been few reports about zero-shrinkage sintering techniques. In this study, ceramic substrate with minimal x– y shrinkage was prepared by glass infiltration method with ‘Al 2O 3/glass/Al 2O 3’ structure. Glass infiltration into alumina particle layer was observed with variation of both sintering temperature (700?≤? T sint.?≤?900 °C) and alumina particle size distribution (0.5?≤? D 50?≤?1.8 μm). Since glass had low viscosity enough to infiltrate at 700 °C, infiltration started at that temperature and infiltrated up to 20 μm or so with temperature increase, but infiltration depth did not increase noticeably above 750 °C. Based on these results, when sintered at 900 °C with controlled sheet thickness of both glass and alumina, the shrinkage in x– y direction was calculated as less than 0.2%, with 40% in z direction. Dielectric constant ( ? r) measured 6.19 with quality factor ( Q) of 552 at 1 GHz of frequency. From these results, it is thought that zero-shrinkage ceramic substrates would be obtained without de-lamination. 相似文献
3.
Ceramics have generally been fabricated from powders by shape forming & sintering methods except for glasses and glass ceramics.
Glasses and glass ceramics can be fabricated by melting methods. The melting method has not only higher productivity but also
higher shape forming ability than powder processes via forming & sintering methods. Thus we have reinvestigated melting methods
in binary and ternary oxides systems to fabricate amorphous bulk ceramics and bulk nano composites. We have successfully fabricated
amorphous phases by simple melt solidification methods in ternary eutectic melts in the HfO 2-Al 2O 3-Gd 2O 3system. The present study demonstrates the formation of the amorphous phases in quaternary systems HfO 2-Al 2O 3-Gd 2O 3-Eu 2O 3. Furthermore, we have also succeeded to fabricate nano-structured bulk ceramics, which consisted of constituent oxide grains
with 20–100 nm in size, by post annealing of the amorphous phase. 相似文献
4.
We have studied glass formable region in the Y 2O 3-CaO-Al 2O 3 system. An optimal composition for the amorphous phase formation was found in the pseudo-eutectic 12CaO⋅7Al 2O 3-CaYAlO 4 system. An amorphous bulk plate of 10 × 25 × 1.8 mm was successfully fabricated using a simple molding technique. The fabricated
glass plate showed an IR absorption edge at around 5.6 μm. The crystallization of the glass sample was observed above 890 ∘C by an X-ray diffraction (XRD) and Thermogravimetry and Differential thermal analysis (TG-DTA). 相似文献
5.
A conventional BaO–Nd 2O 3–TiO 2 ceramic of microwave dielectric material was added to rare-earth derived borate glasses (La 2O 3–B 2O 3–TiO 2) for use as LTCC (low temperature co-fired ceramic) materials. The sintering behavior, phase evaluation, and microwave dielectric properties were investigated. It was found that increasing the sintering temperature from 750 to 850 °C led to increases in shrinkage and microwave dielectric properties (≈15 for ? r , >10,000 GHz for Q*f 0 and >94 ppm/ °C for τ f at 7–8 GHz for resonant frequency). The results suggest that a composite with suitable additives for τ f could feasibly be developed as a material for LTCC applications. 相似文献
6.
Glass-ceramics materials of SrO-BaO-Nb2O5-B2O3 system have been prepared by conventional melt-casting followed by controlled crystallization. The crystallization kinetics, phase evolution, microstructure, breakdown strength and dielectric properties have been explored by differential scanning calorimetry (DSC), X-ray diffractometer (XRD), scanning electron microscope (SEM), and multifunction LCR meter. The results reveal that crystallization mechanism of this glass is believed to be three-dimensional interfacial growth. It was observed that predominant crystalline phase is Ba0.39Sr0.61Nb2O6 in these glass-ceramics crystallized at 750 °C, and the grain size increases with increase in crystallization time. The uniform microstructure can be seen clearly in glass-ceramics crystallized at 750 °C for 3 h, and the obtained glass-ceramics was found to possess optimal properties. Moreover, glass-ceramic with a dielectric constant of 58, the dielectric loss of 0.007 and breakdown strength of 1010 kV/cm could be achieved. In addition, energy storage density of glass-ceramics reached a maximal value of 2.62 J/cm3. To our knowledge, studies on SrO-BaO-Nb2O5-B2O3 glass-ceramics without SiO2 as a glass network former are few, and the melting temperature of the B2O3-based glass is lower than that of SiO2-based glass, which is conducive to the purpose of energy saving. These findings indicate that this glass may be a candidate for high energy-storage capacitors. 相似文献
7.
LaNi 0.6Co 0.4O 3 (LNC) is a perovskite-type conducting ceramic oxide, which is an ideal electrode layer for perovskite ferroelectric and piezoelectric
thin and thick film devices, owing to its unique crystal structure that can facilitate film growth and improve fatigue behavior.
When used for thick films, however, one of the drawbacks is its high sintering temperature of above 1200 ∘C, which can lead to severe inter-diffusion. In an attempt to reduce the sintering temperature of LNC without substantially
deteriorating the electrical properties, we have investigated the effects of doping LNC with an appropriate glass addition.
LNC powder was synthesized through a solid state reaction process. Varying amounts of glass compositions were then introduced,
in order to study their effects on densification, microstructure and electrical properties of LNC. The glass compositions
exhibited a strong effect on the sintering behaviors and microstructure, where the density after sintering was improved with
increasing amount of glass addition. While the electrical conductivity was adversely affected by an increasing amount of glass
addition, the composition with optimal glass addition showed a lowered sintering temperature of 950 ∘C, and at the same time maintained a high conductivity of 117 S cm −1. 相似文献
8.
CaO-Al 2O 3-SiO 2 glass-ceramic were prepared by melt quenching technique. The crystallization behavior and properties were studied by means of a non-isothermal, thermal analysis technique, X-ray diffraction and scanning electron microscopy. The influence of sintering temperature on phase formation, microstructure, bending strength, dielectric and thermal properties were determined. The activation energy of crystallization and the Avrami parameter were also discussed. The X-ray diffraction results show that SiO 2 phase could be found in all samples and CaSiO 3 and anorthite phases could only be observed in the samples sintered at above 875°C. The densification of glass-ceramic starts at 730°C after the liquid glass is formed and stops at 803°C. Complete densification was achieved at 875°C and the highest mechanical strength was obtained at 850°C, but density significantly decreased at higher temperatures. The coefficient of thermal expansion and the dielectric constant increase with the increasing sintering temperature. The value of the Avrami parameter (n) is ~1.6 and the apparent activation energy (E) is 298 kJ/mol. 相似文献
9.
Glasses in the ZnO-B 2O 3-MO 3(M = W, Mo) ternary were examined as potential replacements to PbO-B 2O 3-SiO 2-ZnO glass frits with the low firing temperature (500–600 ∘C) for the dielectric layer of a plasma display panels (PDPs). Glasses were melted in air at 950–1150 ∘C in a narrow region of the ternary using standard reagent grade materials. The glasses were evaluated for glass transition
temperature ( T
g
), softening temperature ( T
d
), the coefficient of thermal expansion ( CTE), dielectric constant ( ε
r
), and optical property. The glass transition temperature of the glasses varied between 470 and 560 ∘C. The coefficient of thermal expansion and the dielectric constant of the glasses were in the range of 5–8 × 10 − 6/ ∘C and 8–10, respectively. The addition of MO 3to ZnO-B 2O 3binary could induce the expansion of glass forming region, the reduction of T
g
and the increase in the CTE and the dielectric constant of the glasses. Also, the effect of the addition of MO 3to ZnO-B 2O 3binary on the transmittance in the visible-light region (350–700 nm) was investigated. 相似文献
10.
The glass-ceramic in the Li 2O-Al 2O 3-SiO 2 system has been prepared by melt quenching route. The crystallization kinetics was studied by differential scanning calorimetry. The effects of sintering temperature on the phase transformation, sintering behavior, bulk density, microstructure, thermal expansion, bending strength and dielectric properties were also investigated by X-ray diffractometry and scanning electron microscopy. (Li, Mg, Zn) 1.7Al 2O 4Si 6O 12 is the first crystalline phase forming in the glass-ceramic and transforms to LiAlSi 3O 8 phase at 800 °C. The other two crystalline phases of ZrO 2 and CaMgSi 2O 6 precipitate at 700 and 750 °C, respectively. The densification of this LAS glass-ceramic starts at around 730 °C and stops at about 805 °C. The coefficient of thermal expansion increases with the increasing sintering temperature. The sample sintered at 800 °C for 30 min exhibited excellent properties. The nonisothermal activation energy of crystallization is 149 kJ/mol and the values of Avrami constant (n) are in the range of 3.2 to 3.9. The LAS glass-ceramic sintered at 800 °C for 30 min showed excellent properties. This makes that this material suitable for a number of LTCC applications. 相似文献
11.
Li 2MgTiO 4 (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 B 2O 3 additives and sintering temperature on the microstructure and microwave dielectric properties of LMT ceramics were investigated. The B 2O 3 additive forms a liquid phase during sintering, which decreases the sintering temperature from 1250°C to 925°C. The LMT ceramic with 8 wt% B 2O 3 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% B 2O 3 and 20 wt% Ag powder demonstrated good chemical compatibility. Therefore, the LMT ceramics with 8 wt% B 2O 3 sintered at 925°C for 4 h is suitable for LTCC applications. 相似文献
12.
Abstract There has been increasing interest in ferroelectric lead zirconate titanate (PZT) films for the applications in piezoelectric and pyroelectric devices. Many potential applications require a film thickness of above 10 μm for higher force, better sensitivity and stability. But it is very difficult to fabricate the PZT thick film on the silicon substrate because of the volatility of PbO and the interdiffusion of the Pb and Si through the bottom electrode during the sintering at normal temperatures (such as above 1200°C). We speculated densification and reaction mechanism of the PZT thick films fabricated at relatively low temperature (under 1000°C) without sintering aids. The PZT thick films were screen-printed on Pt / Al 2O 3 substrate using a paste of PbO, ZrO 2 and TiO 2 powder mixture. Highly densified PZT thick films could be fabricated on Pt / Al 2O 3 substrate at 1000°C, and we achieved the density, remanent polarization, coercive field, dielectric permittivity, dissipation factor and breakdown field of 98%, 10 μC/cm 2 and 20 kV/cm, 540, 0.009 and 15 MV/m, respectively. The results show the possibility of densification of the PZT thick film at relatively low temperature without sintering aids, and the results are promising for the use of PZT thick films in various applications. 相似文献
13.
In this work the synthesis of anorthite-diopside glass-ceramics (GCs) was carried out via sintering and crystallization of
glass powder compacts in the temperature interval 800°C and 950°C. Glass powder compacts with mean particle size of 2 μm were
prepared. The effects of adding TiO 2 and P 2O 5 on the sintering behavior of glass powder compacts and on the properties of resultant glass-ceramics were studied. Mechanical,
thermal, chemical and dielectric properties of sintered GCs were investigated with the aim to evaluate the potential of the
GCs as substrate materials for microelectronics applications. 相似文献
14.
Piezoelectric properties of Al 2O 3-doped Pb(Mn 1/3Nb 2/3)O 3-PbZrO 3-PbTiO 3 ceramics were investigated. The constituent phases, microstructure, electromechanical coupling factor, dielectric constant,
piezoelectric charge and voltage constants were analyzed. Diffraction peaks for (002) and (200) planes were identified by
X-ray diffractometer for all the specimens doped with Al 2O 3. The highest sintered density of 7.8 g/cm 3 was obtained for 0.2 wt% Al 2O 3-doped specimen. Grain size increased by doping Al 2O 3 up to 0.3 wt%, and it decreased by more doping. Electromechanical coupling factor, dielectric constant, piezoelectric charge
and voltage constants increased by doping Al 2O 3 up to 0.2 wt%, and it decreased by more doping. This might result from the formation of oxygen vacancies due to defects in
O 2 − ion sites and the substitution of Al 3+ ions. 相似文献
15.
The electrical properties of a ceramic varistor depend strongly on its microstructural uniformity. In the present study, the microstructure of the Bi 2O 3-doped ZnO after sintering is characterized. A very small amount, 0.04 mol%, of Bi 2O 3-addition may induce density inhomogeneity in the early stage of sintering. A critical amount, >0.09 mol%, of Bi 2O 3 is needed to result in density uniformity. The addition of Bi 2O 3 can enhance the coarsening rate of ZnO grains; nevertheless, the grain size distribution is not affected. 相似文献
16.
Future-generation memory devices will require materials with higher dielectric constants compared to conventional dielectric materials such as silicon oxide and silicon nitride. Tantalum oxide (Ta 2O 5) is one of the most promising high dielectric constant materials because of its ease of integration into conventional VLSI processes compared to other complex oxide dielectrics. The dielectric constant and thermal stability characteristics of bulk Ta 2O 5 samples were previously reported to enhance significantly through small substitutions of Al 2O 3. However, this improvement in the dielectric constant of (1 – x)Ta 2O 5- xAl 2O 3 was not clearly understood. The present research attempts to explain the higher dielectric constant of (1 – x)Ta 2O 5- xAl 2O 3 by fabricating thin films with enhanced dielectric properties. A higher dielectric constant of 42.8 was obtained for 0.9Ta 2O 5-0.1Al 2O 3 thin films compared to that reported for pure Ta 2O 5 (25–30). This increase was shown to be closely related to a-axis orientation. Pure Ta 2O 5 thin films with similar a-axis orientation also exhibited a high dielectric constant of 51.7, thus confirming the orientation effect. Systematic study of dielectric and insulating properties of (1 – x)Ta 2O 5- xAl 2O 3 thin films indicate improved leakage current properties and reliability characteristics such as temperature coefficient of capacitance and bias stability with increase in Al 2O 3 concentrations. 相似文献
17.
In the present study, a new procedure, arc-melting followed by spark plasma sintering, was employed to prepare BaTi 2O 5 ceramics with high relative density and large dimension. Single-phased BaTi 2O 5 powders were synthesized from BaCO 3 and TiO 2 powders by arc-melting, and then the BaTi 2O 5 powders were densified by spark plasma sintering at different temperatures (1273-1473?K) and pressures (20-50?MPa). Single-phased BaTi 2O 5 ceramic was obtained at and below 1423?K, however, it tended to decompose at elevated temperatures. Considering the upperbound decomposing temperature, we further enhanced the densification of BaTi 2O 5 ceramics by increasing the sintering pressure, and a high relative density of 92.1?% was achieved at 50?MPa. The permittivity of the BaTi 2O 5 ceramics was 28.7 at 1?MHz, and increased with the measuring temperature, reaching a maximum value of 191 at the Curie temperature of?~?740?K. 相似文献
18.
Dielectric ceramics of Mg 2TiO 4 (MTO) were prepared by solid-state reaction method with 0.5–1.5 wt.% of La 2O 3 or V 2O 5 as sintering aid. The influences of La 2O 3 and V 2O 5 additives on the densification, microstructure and microwave dielectric properties of MTO ceramics were investigated. It is found that La 2O 3 and V 2O 5 additives lowered the sintering temperature of MTO ceramics to 1300 °C and 1250 °C respectively, whereas the pure MTO exhibits highest density at 1400 °C. The reduction in sintering temperature with these additives was attributed to the liquid phase effect. The average grain sizes of the MTO ceramics added with La 2O 3, and V 2O 5 found to decrease with an increase in wt%. The dielectric constant (ε r) was not significantly changed, while unloaded Q values were affected with these additives, and the values were in the range of 92,000–157,550 GHz and 98,000–168,000 GHz with the addition of La 2O 3 and V 2O 5, respectively. The dielectric properties are strongly dependent on the densification and the microstructure of the MTO ceramics. The decrease in Q× f o value at higher concentration of La 2O 3 and V 2O 5 addition was owing to inhomogeneous grain growth and the liquid phase which is segregated at the grain boundary. In comparison with pure MTO ceramics, La 2O 3 and V 2O 5 additives effectively improved the densification and dielectric properties with lowering of sintering temperature. The proposed loss mechanisms suggest that the oxygen vacancies and the average grain sizes are the influencing factors in the dielectric loss of MTO ceramics. 相似文献
19.
The effect of the addition of glass on the densification, low temperature sintering, and microwave dielectric properties of
the Ca[(Li 1/3Nb 2/3) 1−x
Ti x]O 3−δ(CLNT) was investigated. Addition of glass (B 2O 3-ZnO-SiO 2-PbO system) improved the densification and reduced the sintering temperature from 1150 ∘C to 900 ∘C of Ca[(Li 1/3Nb 2/3) 1−x
-Ti x]O 3−δ microwave dielectric ceramics. As increasing glass contents from 10 wt% to 15 wt%, the dielectric constants (ε r) and bulk density were increased. The quality factor (Q⋅f 0), however, was decreased slightly. The temperature coefficients of the resonant frequency (τ f) shifted positive value as increasing glass contents over Ti content is 0.2 mol. The dielectric properties of Ca[(Li 1/3Nb 2/3) 0.75Ti 0.25]O 3−δ with 10 wt% glass sintered at 900 ∘C for 3 h were ε r = 40 Q·f 0 = 11500 GHz, τ f = 8, ppm/°C. The relationship between the microstructure and dielectric properties of ceramics was studied by X-ray diffraction
(XRD), and scanning electron microscope (SEM). 相似文献
20.
NASICON-type Li 1.4Al 0.4Ti 1.6(PO 4) 3 solid electrolytes were prepared by various processes, such as crystallization of glasses, spark plasma sintering (SPS) and conventional sintering process from nanosized precursor powders synthesized by a sol–gel route. The experimental results showed that grain size and relative density were the main factors determining the ionic conductivity of the bulk materials. The SPS technique produced ceramics with nearly 100% of the theoretical density. Maximum room temperature conductivities, 1.39?×?10 ?3 S cm ?1 and 1.12?×?10 ?3 S cm ?1 of grain boundary conductivity and total conductivity, respectively were obtained which were the highest values for Li + inorganic oxide conductors as reported. Crystallization of ceramics from a glass was also certified as a favorable route to fabricate a bulk material with high conductivity. 相似文献
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