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1.
The processing conditions, reaction mechanism, fine structure of the powders, microstructure, and dielectric properties of SrBiNb 2O 9 (SBN) were systematically studied. A relative density of >80% was obtained using a two-step sintering process at moderate pressure. XRD showed that a single phase with the layered perovskite structure of SrBi 2Nb 2O 9 (SBN) was formed after calcining at 600 °C. No intermediate phase was found during heat treatment at and above 600 °C. The crystallite size ( D) and the effective strain ( η) were found to be 38.8 nm and 0.01475, respectively, while the particle size obtained from TEM was laid between 25 and 36 nm. SEM revealed that the average grain size after sintering at 900 °C for 4 h was 0.67 μm. Dielectric constant and corresponding tangent loss were measured in the frequency range from 1 kHz to 1 MHz from which the Curie temperature ( Tc) was found to be at 450 °C. 相似文献
2.
The dielectric constants (K) of ceramics composition (Nb 2O 5)( 1-x): xTiO 2, (x = 0.05, 0.08, 0.11) have been measured over the temperature range from -180 °C to 180 °C in the frequency range 100 Hz-IMHz. For all three samples, the temperature dependence of the dielectric constants at various frequencies shows the dielectric dispersion and the frequency dependent dielectric losses are observed, suggesting the several relaxation phenomena. Dielectric loss data are analyzed by Arrhenius formalism indicating the presence of relaxation type dielectric mechanisms in (Nb 2O 5)( 1-x): xTiO 2 ceramics. 相似文献
3.
This article discusses a mechanism for preparing perovskite powders, 0.75Pb(Ni 1/3Nb 2/3)O 3-0.25PbTiO 3 (PNN-PT), using a semichemical method (SCM).Precursors were prepared by adding aqueous Ni(Ac) 2 solutions to an alcohol slurry of PbO, Nb 2O 5, and TiO 2. The TG-DTG and DSC analysis of the precursors and XRD analysis of the powders at different thermal treatment temperatures showed that the reaction mechanisms in this method differ from those in the conventional mixed-oxide method. The aqueous Ni(Ac) 2 solution reacted with PbO to form Pb(Ac) 2 · Pb(OH) 2 · H 2O and Ni(OH) 2, which decomposed to form nascent PbO and NiO, thereby improving the reactivity and distribution of PbO and NiO. Pb 3Nb 2O 8 and NiNb 2O 6 formed and were easily converted into the perovskite phase during the thermal treatment process. At a thermal treatment temperature of 850°C, the content of the perovskite phase reached 98%. Pyrochlore-free PNN-PT ceramic was obtained after 2 h of sintering at 1100°C, and its dielectric properties were found to be excellent at temperatures ranging between -55 and 120°C. 相似文献
4.
Temperature dependence of dielectric permittivity and electric conductivity of polycrystalline PbCd 1/3Nb 2/3O 3 in the region of phase transition have been presented. Electric properties of polycrystalline PbCd 1/3Nb 2/3O 3 depend on frequency of the measuring field. In the region of para-ferroelectric phase transition a change of electric properties takes place. 相似文献
5.
The effects of a forming atmosphere on the stability, the sintering and the dielectric properties of Ba 5Nb 4O 15, BaNb 2O 6, ZnNb 2O 6 and Zn 3Nb 2O 8 ceramics were investigated, because of the primary importance of the sintering atmosphere in relation to copper sintering. These Nb-based materials were sintered in air and in Ar/H 210%. Zn-containing samples are very sensitive to the reductive atmosphere. ZnO volatilises at 800–850 °C and the resulting compound does not exhibit the expected properties. BaNb 2O 6 and Ba 5Nb 4O 15 are more stable in term of relative weight loss. Nevertheless, the phase analysis reveals a modification of the BaNb 2O 6 phase, what induces the degradation of the dielectric property stability versus temperature. The properties of Ba 5Nb 4O 15 are not modified by a sintering in reductive atmosphere. A relative permittivity of 38.8, a permittivity temperature coefficient of −150 ppm °C −1 and an insulating resistivity of 10 10.9 Ω cm were obtained for this latter. 相似文献
6.
X-ray and optical measurements are used to show that the spontaneous strain (b/a-1) and optical birefringence Δn ab in single crystals of ferroelectric PbBi 2Nb 2O 9 are a function of the state of electrical poling, going to a zero in the unpoled state. In poled crystals all spontaneous strain is lost at a temperature ≃200°C below the dielectric Curie temperature in a manner reminiscent of the behavior of the perovskite relaxor ferroelectrics which have diffuse phase transitions. 相似文献
7.
Since the electromechanical devices move towards enhanced power density, high mechanical quality factor ( Qm) and electromechanical coupling factor ( kp) are commonly needed for the high powered piezoelectric transformer with Qm≥2000 and kp=0.60. Although Pb(Mn 1/3Nb 2/3)O 3–PbZrO 3–PbTiO 3 (PMnN–PZ–PT) ceramic system has potential for piezoelectric transformer application, further improvements of Qm and kp are needed. Addition of 2CaO–Fe 2O 3 has been proved to have many beneficial effects on Pb(Zr,Ti)O 3 ceramics. Therefore, 2CaO–Fe 2O 3 is used as additive in order to improve the piezoelectric properties in this study. The piezoelectric properties, density and microstructures of 0.07Pb(Mn 1/3Nb 2/3)O 3–0.468PbZrO 3–0.462PbTiO 3 (PMnN–PZ–PT) piezoelectric ceramics with 2CaO–Fe 2O 3 additive sintered at 1100 and 1250 °C have been studied. When sintering temperature is 1250 °C, Qm has the maximum 2150 with 0.3 wt.% 2CaO–Fe 2O 3 addition. The kp more than 0.6 is observed for samples sintered at 1100 °C. The addition of 2CaO–Fe 2O 3 can significantly enhance the densification of PMnN–PZ–PT ceramics when the sintering temperature is 1250 °C. The grain growth occurred with the amount of 2CaO–Fe 2O 3 at both sintering temperatures. 相似文献
8.
The influence of sintering and poling conditions on dielectric properties and microstructures of the system 0·125Pb(Mg 1/3Nb 2/3)O 3−0·875Pb (Zr 0·5Ti 0·5)O 3 was investigated. Specimens were prepared by the conventional mixed-oxide technique. On account of eliminating the pyrochlore phase and lowering the sintering temperature, the calcined 0·125PZT−0·875PMN ceramic was doped with 4PbO.B 2O 3 glass powder. The 4PbO.B 2O 3 glass frit not only has a low flow temperature, but also a high polarizability. Additions of 4PbO.B 2O 3 to the perovskite 0·125PMN–0·875PZT solid solution will form a liquid phase, which served as a densification aid for the ceramics. With additions of 0·2 wt% glass frit, densities in excess of 98% of theoretical were obtained after sintering at 115°C. By variation of the fabrication processes, the influence of sintering and poling conditions on the properties of the ceramics was studied. 相似文献
9.
In this study, in order to develop low-temperature sintering ceramics for a multilayer piezoelectric transformer application, we explored CuO and Bi 2O 3 as sintering aids at low temperature (900 °C) sintering condition for Sb, Li and Mn-substituted 0.8Pb(Zr 0.48Ti 0.52)O 3–0.16Pb(Zn 1/3Nb 2/3)O 3–0.04Pb(Ni 1/3Nb 2/3)O 3 ceramics. These substituted ceramics have excellent piezoelectric and dielectric properties such as d33 347 pC/N, kp 0.57 and Qm 1469 when sintered at 1200 °C. The addition of CuO decreased the sintering temperature through the formation of a liquid phase. However, the piezoelectric properties of the CuO-added ceramics sintered below 900 °C were lower than the desired values. The additional Bi 2O 3 resulted in a significant improvement in the piezoelectric properties. The composition Sb, Li and Mn-substituted 0.8Pb(Zr 0.48Ti 0.52)O 3–0.16Pb(Zn 1/3Nb 2/3)O 3–0.04Pb(Ni 1/3Nb 2/3)O 3 + 0.5 wt% CuO + 0.5 wt% Bi 2O 3 showed the value of kp = 0.56, Qm = 1042 (planar mode), d33 = 350 pC/N, when it was sintered at 900 °C for 2 h. These values indicated that the newly developed composition might be suitable for multilayer piezoelectric transformer application. 相似文献
10.
A suspension stabilizer-coating technique was employed to prepare x mol% Yb 2O 3 ( x = 1.0, 2.0, 3.0 and 4.0) and 1.0 mol% Y 2O 3 co-doped ZrO 2 powder. A systematic study was conducted on the sintering behaviour, phase assemblage, microstructural development and mechanical properties of Yb 2O 3 and Y 2O 3 co-doped zirconia ceramics. Fully dense ZrO 2 ceramics were obtained by means of pressureless sintering in air for 1 h at 1450 °C. The phase composition of the ceramics could be controlled by tuning the Yb 2O 3 content and the sintering parameters. Polycrystalline tetragonal ZrO 2 (TZP) and fully stabilised cubic ZrO 2 (FSZ) were achieved in the 1.0 mol% Y 2O 3 stabilised ceramic, co-doped with 1.0 mol% Yb 2O 3 and 4.0 mol% Yb 2O 3, respectively. The amount of stabilizer needed to form cubic ZrO 2 phase in the Yb 2O 3 and Y 2O 3 co-doped ZrO 2 ceramics was lower than that of single phase Y 2O 3-doped materials. The indentation fracture toughness could be tailored up to 8.5 MPa m 1/2 in combination with a hardness of 12 GPa by sintering a 1.0 mol% Yb 2O 3 and 1.0 mol% Y 2O 3 ceramic at 1450 °C for 1 h. 相似文献
11.
Bearing in mind the excellent dielectric properties at high frequency of some niobates like ZnNb 2O 6, Zn 3Nb 2O 8, BaNb 2O 6, Ba 5Nb 4O 15 ( r 20–45, tan δ < 10 × 10 −4 and ρi > 10 10 Ω cm), synthesis, sintering and properties of these oxides are reported. The lowering of their sintering temperature has been investigated for these four ceramics using sintering aids. Using appropriate additive, it is possible to densify these ceramics at a temperature for which base metal electrodes, e.g. Cu and Ag can be employed. Two formulations were found to be sinterable at 1000 °C (lower than the copper melting point) whereas a third formulation is co-sinterable with silver electrodes. For this later, the dielectric properties are globally maintained in comparison with the pure compound sintered at 1200 °C. This result makes this formulation suitable for silver based passive components devices manufacturing. 相似文献
12.
In this work, Cu 2Ta 4O 12 ceramic was investigated as a promising, lead-free, nonferroelectric material with high dielectric permittivity. The results of impedance spectroscopy studies carried out at frequencies 10 Hz to 2 MHz over a wide temperature range from −55 to 700 °C were analyzed in the impedance, dielectric permittivity and electric modulus formalisms. In complex impedance plots two distinct arcs were distinguished, ascribed to the semiconducting grains and to the insulating grain boundaries. Cu 2Ta 4O 12 ceramic was found to exhibit a high dielectric permittivity exceeding 10,000 at low frequencies in the temperature range 150–740 °C. High permittivity of this material was attributed to the formation of internal (grain boundary) barrier layer capacitors. The influence of sintering conditions on microstructure, composition and dielectric properties of Cu 2Ta 4O 12 ceramics was also studied. 相似文献
13.
The sintering behavior and dielectric properties of the monoclinic zirconolite-like structure compound Bi 2(Zn 1/3Nb 2/3) 2O 7 (BZN) and Bi 2(Zn 1/3Nb 2/3−xV x) 2O 7 (BZNV, x = 0.001) sintered under air and N 2 atmosphere were investigated. The pure phase were obtained between 810 and 990 °C both for BZN and BZNV ceramics. The substitution of V 2O 5 and N 2 atmosphere accelerated the densification of ceramics slightly. The influences on microwave dielectric properties from different atmosphere were discussed in this work. The best microwave properties of BZN ceramics were obtained at 900 °C under N 2 atmosphere with r = 76.1, Q = 850 and Qf = 3260 GHz while the best properties of BZNV ceramics were got at 930 °C under air atmosphere with r = 76.7, Q = 890 and Qf = 3580 GHz. The temperature coefficient of resonant frequency τf was not obviously influenced by the different atmospheres. For BZN ceramics the τf was −79.8 ppm/°C while τf is −87.5 ppm/°C for BZNV ceramics. 相似文献
14.
Dispersing La 2O 3 on δ- or γ-Al 2O 3 significantly enhances the rate of NO reduction by CH 4 in 1% O 2, compared to unsupported La 2O 3. Typically, no bend-over in activity occurs between 500° and 700°C, and the rate at 700°C is 60% higher than that with a Co/ZSM-5 catalyst. The final activity was dependent upon the La 2O 3 precursor used, the pretreatment, and the La 2O 3 loading. The most active family of catalysts consisted of La 2O 3 on γ-Al 2O 3 prepared with lanthanum acetate and calcined at 750°C for 10 h. A maximum in rate (mol/s/g) and specific activity (mol/s/m 2) occurred between the addition of one and two theoretical monolayers of La 2O 3 on the γ-Al 2O 3 surface. The best catalyst, 40% La 2O 3/γ-Al 2O 3, had a turnover frequency at 700°C of 0.05 s −1, based on NO chemisorption at 25°C, which was 15 times higher than that for Co/ZSM-5. These La 2O 3/Al 2O 3 catalysts exhibited stable activity under high conversion conditions as well as high CH 4 selectivity (CH 4 + NO vs. CH 4 + O 2). The addition of Sr to a 20% La 2O 3/γ-Al 2O 3 sample increased activity, and a maximum rate enhancement of 45% was obtained at a SrO loading of 5%. In contrast, addition of SO =4 to the latter Sr-promoted La 2O 3/Al 2O 3 catalyst decreased activity although sulfate increased the activity of Sr-promoted La 2O 3. Dispersing La 2O 3 on SiO 2 produced catalysts with extremely low specific activities, and rates were even lower than with pure La 2O 3. This is presumably due to water sensitivity and silicate formation. The La 2O 3/Al 2O 3 catalysts are anticipated to show sufficient hydrothermal stability to allow their use in certain high-temperature applications. 相似文献
15.
Dielectric permittivity along the [111] direction has been measured as a function of temperature for a relaxor ferroelectric single crystal (PbMg 1/3Nb 2/3O 3) 0.67(PbTiO 3) 0.33 (PMN-33%PT). A sharp ferroelectric phase transition was observed near 425 K and 429 K for cooling and heating processes, respectively. As temperature decreases, a diffuse phase transition (which begins near 330 K upon cooling) was detected. In addition, the nature of the thermal hysteresis for the dielectric permittivity confirms that these transitions (near 330 and 425 K upon cooling) are diffuse first-order and first-order, respectively. The frequency-dependent dielectric data ε' 111 (ƒ, T) prove the existence of an electric dipolar relaxation process between 350 and 400 K. The activation energy, the Vogel-Fulcher temperature and attempt frequency corresponding to this relaxation process are also calculated. 相似文献
16.
Relaxor perovskite ceramics of lead magnesium niobate (PMN) and lead iron niobate (PFN) have been prepared by employing a two-step mixed oxide synthetic route, followed by the application of a two-stage sintering method. The effect of the latter on phase formation, densification behaviour, microstructure and dielectric properties of both relaxor systems is examined. Two types of pyrochlore phase are found to co-exist with the major phase in the PMN system, i.e. Pb 3Nb 4O 13 and Pb 1·83Nb 1·71Mg 0·29O 6·39 with an MgO inclusion. By comparison, a PbFe 8O 13 pyrochlore phase with an Fe 2O 3 inclusion is observed in the PFN system. The types and concentrations of phases present are found to depend upon sintering conditions. In connection with dielectric properties, a substantial dependence of the maximum values of both relative permittivity (′ r,max) and dissipation factor (tanδ max) on sintering regime is observed. By employing optimised two-stage sintering conditions, high density ceramics with low firing temperatures and reasonable relative permittivities can be achieved in both systems. 相似文献
17.
The system Al 2O 3–ZrO 2 was studied by differential thermal analysis in inert atmosphere and in vacuum. The eutectic was located at 1866°C and 40% mass of ZrO 2. Zirconia solid solution at the eutectic temperature is up to 1.1±0.3% mass of Al 2O 3. Enthalpy of melting of this eutectic is 1080±90 J/g. Pure ZrO 2 transforms from monoclinic to tetragonal at 1162±7°C, but the saturated solid solution of ZrO 2, with 0.7±0.2% mass Al 2O 3 at this temperature, transforms at 1085±5°C. Inverse transitions occur with hysteresis correspondingly at 1055±5 and 995±5°C. Enthalpy of transformation of pure ZrO 2 from monoclinic to tetragonal phase is 42±5 J/g (5.2±0.6 J/mol) but only 30±5 J/g for a ZrO 2 saturated solid solution. 相似文献
18.
A series of CuO–ZnO/Al 2O 3 solids were prepared by wet impregnation using Al(OH) 3 solid and zinc and copper nitrate solutions. The amounts of copper and zinc oxides were varied between 10.3 and 16.0 wt% CuO and between 0.83 and 7.71 wt% ZnO. The prepared solids were subjected to thermal treatment at 400–1000°C. The solid–solid interactions between the different constituents of the prepared solids were studied using XRD analysis of different calcined solids. The surface characteristics of various calcined adsorbents were investigated using nitrogen adsorption at −196°C and their catalytic activities were determined using CO-oxidation by O 2 at temperatures ranged between 125°C and 200°C. The results showed that CuO interacts with Al2O3 to produce copper aluminate at ≥600°C and the completion of this reaction requires heating at 1000°C. ZnO hinders the formation of CuAl2O4 at 600°C while stimulates its production at 800°C. The treatment of CuO/Al2O3 solids with different amounts of ZnO increases their specific surface area and total pore volume and hinders their sintering (the activation energy of sintering increases from 30 to 58 kJ mol−1 in presence of 7.71 wt% ZnO). This treatment resulted in a progressive decrease in the catalytic activities of the investigated solids but increased their catalytic durability. Zinc and copper oxides present did not modify the mechanism of the catalyzed reaction but changed the concentration of catalytically active constituents (surface CuO crystallites) without changing their energetic nature. 相似文献
19.
To establish the correct reaction sequence of BaO–Sm 2O 3–4TiO 2, phases present in different calcining temperatures are identified by X-ray diffraction patterns. When different calcining temperatures are used, the source phase BaO (BaCO 3) consumes below 850°C, the source phases TiO 2 and Sm 2O 3 consume at 1000 and 1150°C; the intermediate phases BaTiO 3, BaTi 4O 9, and Sm 2Ti 2O 7 consume at 1050, 1200, and 1250°C, respectively. The BaSm 2Ti 4O 12 phase starts to reveal at the 1100°C-calcined powder. The integrating intensity of BaSm 2Ti 4O 12 phase increases with the raising of calcining temperatures, accompanying with the decrease of integrating intensities of the source and intermediate phases. As the sintering temperature increases, the densities, quality values, and dielectric constants of BaSm 2Ti 4O 12 ceramics increase and saturate at 1325 oC. The BaSm 2Ti 4O 12 ceramics sintered at 1325°C have the properties of Q*f=5180, r=81.8, and τ f=−19.2 ppm/°C. 相似文献
20.
PbO-CaO-B 2O 3-SiO 2系玻璃粉体是耐高过载低温共烧陶瓷(LTCC)生瓷带的主要组成部分。玻璃粉体的析晶行为影响烧结性能,进而决定基板的使用性能。本文研究了Al 2O 3含量对PbO-CaO-B 2O 3-SiO 2系玻璃析晶行为与烧结性能的影响。结果表明:向PbO-CaO-B 2O 3-SiO 2系玻璃中引入Al 2O 3可抑制玻璃析晶,防止高膨胀晶相的析出,并提高玻璃烧结密度;不含Al 2O 3的PbO-CaO-B 2O 3-SiO 2玻璃粉体析晶峰温度为862 ℃,烧结过程中析出方石英晶相,20~200 ℃的平均线膨胀系数高达260.8×10 -7 ℃ -1;引入2.1%(质量分数)Al 2O 3可显著抑制玻璃析晶,700 ℃烧结后膨胀系数降低至72.9×10 -7 ℃ -1,介电常数显著增大,由6.30提高至7.02。 相似文献
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