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1.
A series of ceramics with a general formula Ca 1+xLa 4?xNb xTi 5?xO 17 (0 ≤ x ≤ 4) were fabricated using the solid-state ceramic route. The phase, microstructure, and microwave dielectric properties varied distinctly with composition or the value of x. X-ray diffraction results showed that the two end member phases, CaLa 4Ti 5O 17 and Ca 5Nb 4TiO 17, crystallized into single phases with orthorhombic and monoclinic crystal structure, respectively. For intermediate compounds with x = 1, 2, and 3, mixture phases CaLa 4Ti 5O 17 and Ca 5Nb 4TiO 17 coexisted and a trace amount of second phase was detected. The ceramics showed high ε r in the range of 45–52, relatively high quality factors with Q × f in the range of 9,870–15,680 GHz and τ f value in the range between ?38 and ?126.4 ppm/°C. τ f of CaLa 4Ti 5O 17 can be tuned to a near-zero value by addition of suitable amount of TiO 2. 相似文献
2.
5BaO–2V 2O 5 ceramic has been prepared by conventional solid state reaction method. The X-ray diffraction and Laser Raman studies have been carried out to ascertain the phase purity and crystal structure of the prepared composition. The microwave dielectric properties of the well sintered ceramic compacts were measured by Hakki & Colemann post resonator and cavity perturbation techniques using a vector network analyzer. The 5BaO–2V 2O 5 ceramic exhibits a low dielectric constant of 12.1, relatively good quality factor of 26,790 GHz, and a small temperature variation of resonant frequency of 7 ppm/°C in the microwave frequency region. 相似文献
3.
New microwave dielectric ceramics in the SrLa 4?xNd xTi 5O 17 (0 ≤ x ≤ 4) composition series were prepared through a solid state mixed oxide route. All the compositions formed highly dense (~95%) single phase ceramics upon sintering at 1500–1580 °C. The molar volume and theoretical density decreased due to the substitution of small (1.27 Å) Nd ions for large (1.36 Å) La ions. This decrease was associated with a decrease in the dielectric constant ( ?r), temperature coefficient of resonant frequency ( τf) and quality factor ( Qufo). An analysis of properties achieved in the present study indicated that ceramics exhibiting nearly zero τf corresponding to ?r ~ 54 could be fabricated in the SrLa 4?xNd xTi 5O 17 composition series at x ~ 1.6; however, further work is required to improve Qufo (~6000 GHz) for possible practical applications. 相似文献
5.
The effects of ZnO–B 2O 3–SiO 2 glass (ZBS) additions on the sintering behavior and microwave dielectric properties of Ba 2Ti 3Nb 4O 18 ceramic have been investigated. Due to the liquid phase effects resulting from the additives, the addition of ZBS glass can
reduce the sintering temperature of Ba 2Ti 3Nb 4O 18 ceramic from 1,250 to 925 °C and induce no obvious degradation of the microwave dielectric properties. Typically, when 3wt%
ZBS is added, a dense ceramic can be sintered at 925 °C with a ε r of 33.2, a high of Q × f of 13,600 GHz and a low τ
f
of −5.9 ppm/°C. Moreover, ZBS glass-added Ba 2Ti 3Nb 4O 18 ceramic has a chemical compatibility with silver electrode, which suggests that the ceramic could be applied to LTCC devices
application. 相似文献
6.
A new Li 2O–Nb 2O 5–TiO 2 (LNT) ceramic with the Li 2O:Nb 2O 5:TiO 2 mole ratio of 3:1:3 has been investigated. The compound is composed of two phases, the Li 2TiO 3 and “M-phase” solid solution phase. The microwave dielectric ceramic has low sintering temperature (∼1100 °C) and good microwave
dielectric properties of a relatively high permittivity (∼51), high Q × f value up to 8700, and small temperature coefficient (∼37 ppm/°C). The low-amount doping of 0.83Li 2O–0.17V 2O 5 (LV) can effectively lower the sintering temperature from 1100 to 900 °C and induce no obvious degradation of the microwave
dielectric properties. Typically, the 1 wt.% LV-doped ceramic sintered at 900 °C has better microwave dielectric properties
of ε r = 51.3, Q × f = 7235 GHz, τ
f
= 22 ppm/°C, which suggests that the ceramics can be applied in microwave LTCC devices. 相似文献
7.
The stabilization of La2/3TiO3 in the perovskite structure by 4 mol% LaAlO3 resulted in maximum values for the relative permittivity (k72) and temperature coefficient of resonant frequency (f=123 ppm K-1). The Q-value quality factor of these ceramics were over 5300 measured at 4.5 GHz. Higher contents of LaAlO3 cause a decrease in both the permittivity and f values, accompanied by an increase in the Q-value. Typical values measured at 6.0 GHz for ceramics with the composition 70 mol% La2/3TiO3 – 30 mol% LaAlO3 are k>44, f=+7 ppm K-1 and Q>5500. The results depend on the processing parameters. The sintering temperature increases with increasing LaAlO3 content. An oxidizing sintering atmosphere improves the Q-value, whereas the permittivity and f are not significantly affected. 相似文献
11.
In this work, (1?x)Mg2SiO4–xCa1?ySm2y/3TiO3 ceramics were fabricated using the conventional solid-state reaction method. When y?=?0.2, the effects of Ca1?ySm2y/3TiO3 contents on microstructure, phase evolution, and microwave dielectric properties of the samples were studied. The X-ray diffraction showed that Mg2SiO4 and Ca0.8Sm0.4/3TiO3 co-existed in composite ceramics. The dielectric constant (εr) and temperature coefficient of resonant frequency (τf) increased with the increasing content of Ca0.8Sm0.4/3TiO3, while the quality factor (Q?×?f) decreased. At x?=?0.22, the (1?x) Mg2SiO4–xCa0.8Sm0.4/3TiO3 ceramics sintered at 1325?°C for 3?h possessed optimal microwave dielectric properties: εr?~?11.89, Q?×?f value?~?32,703?GHz and τf?~?+?0.49?ppm/°C. As a result, the εr of (1?x) Mg2SiO4?+?xCa1?ySm2y/3TiO3 ceramics could be adjusted in the range of 10.83 to 13.88 while the τf is near-zero. 相似文献
12.
(1 ? y)[0.5ZnNb 2O 6–0.5Zn 3Nb 2O 8]– yZnTa 2O 6 with y = 0.91 (ZNT) ceramic have been prepared by conventional solid state ceramic route. The effect of glass additives on the microstructure, densification, and microwave dielectric properties of the ZNT ceramic for low temperature co-fired ceramic applications was investigated. Different weight percentages of quenched glass such as ZnO–B 2O 3–SiO 2, BaO–B 2O 3–SiO 2, LiO–B 2O 3–SiO 2 and MgO–B 2O 3–SiO 2 were added to ZNT powder. The crystal structure of the ceramic–glass composites was studied by X-ray diffraction and microstructure by scanning electron microscopy. The microwave dielectric properties such as relative permittivity (ε r), quality factor (Q uxf) and co-efficient of temperature variation of resonant frequency (τ f) of the ceramics have been measured in the frequency range 4–6 GHz. The 5 wt% ZnO–B 2O 3–SiO 2 added ZNT ceramic sintered at 900 °C showed: ε r = 28.1, Q uxf = 32820 GHz (at 4.92 GHz), and τ f = ?7.7 ppm/ oC respectively. 相似文献
13.
Tin niobiophosphate glasses were produced using a domestic microwave oven under a nitrogen flow. The fast microwave melting
method and the protective atmosphere prevent the oxidation of SnO. After 10 min of heating, the NaPO 3, SnO, and Nb 2O 5 mixtures are homogeneous and permit to obtain transparent glasses. Three series of glasses with different Sn/Nb ratio were
studied to determine the influence of each oxide. The glass transition temperature increases linearly with the amount of Nb 2O 5 and SnO. These variations are more important for compositions with high metallic cation proportions and with a low Sn/Nb
ratio. The same evolutions were observed for the density, Vickers hardness, and elastic modulus while the thermal expansion
coefficient decreases monotonously. The simultaneous insertion of SnO and Nb 2O 5 in phosphate glass matrix leads to a progressive strengthening of the glass network. The chemical durability of the glasses
also increases as a function of the amount of metal oxides. We prepared a bulk glass sample with a dissolution rate of about
3.3 × 10 −8 g cm −2 min −1 in renewed water conditions at 95 °C. This durability is equivalent to those of the window glass whereas the glass transition
temperature remains lower than 485 °C. 相似文献
14.
Effects of 1.0 wt.% V 2O 5–CuO mixture addition on the sintering behavior, phase composition and microwave dielectric properties of BiSbO 4 ceramics have been investigated. BiSbO 4 ceramics can be well densified below temperature about 930 °C with 1.0 wt.% V 2O 5–CuO mixtures addition with different ratios of CuO to V 2O 5. The formation of BiVO 4 phase and substitution of Cu 2+ can explain the decrease of sintering temperature. Dense BiSbO 4 ceramics sintered at 930 °C for 2 h exhibited good microwave dielectric properties with permittivity between 19 and 20.5, Qf values between 19,000 and 40,000 GHz and temperature coefficient of resonant frequency shifting between ?71.5 ppm °C ?1 and ?77.8 ppm °C ?1. BiSbO 4 ceramics could be a candidate for microwave application and low temperature co-fired ceramics technology. 相似文献
17.
The effect of SrO–B 2O 3–SiO 2 glass additive (SBS) on the microstructure and dielectric properties of CaCu 3Ti 4O 12 (CCTO) ceramics was investigated. This SBS–added CCTO ceramics were prepared by the solid state reaction. The undesirable
impurity phases Ca 3SiO 5 started appearing in the XRD patterns, suggesting a possible chemical reaction between CaTiO 3 and SiO 2 (the devitrification production of SBS glass). The SBS glass additive promoted the grain growth and densification of CCTO
ceramics. Cole–Cole plots of conductance suggested that the resistivity grain boundary decreased with increasing amount of
SBS glass (when x = 0–2 wt%), then increased (when x = 2–3 wt%). The addition of SBS glass was desirable to increase the dielectric constants (up to 10 4) and lowered the dielectric losses of CCTO over the frequency range of 450–40 kHz at the relatively lower sintering temperature
for relatively shorter sintering time (1,050 °C, 12 h). 相似文献
19.
The microwave dielectric properties of BaO–TiO 2–ZnO (BTZ) system ceramics were studied as a function of the amount of Nb 2O 5 dopant. With the addition of 0–0.025 mol% Nb 2O 5, the substitution of Ti 4+ ions with Nb 5+ ions decreased the sintering temperature and increased the dielectric constant ε r and quality factor Q of the system due to the similar atomic radius of Nb 5+ and Ti 4+ ions. When the amount of Nb 5+ increased further (>0.025 mol%), Q was decreased by increasing the titanium vacancies. When the system doped with 0.025 mol%
Nb 2O 5 was sintered at 1160 °C for 6 h, the ε r, Qf 0, and the temperature coefficient of resonant frequency (τ f) were 36.7, 41,000 GHz, and −5.0 ppm/°C, respectively, at 5 GHz. 相似文献
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