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1.
Preparation of Undoped Lead Titanate Ceramics via Sol-Gel Processing   总被引:1,自引:0,他引:1  
Crack-free, undoped PbTiO3 ceramics were fabricated successfully using sol–gel-synthesized powder prepared from chelated titanium alkoxide and lead acetate. The sintered ceramics, 8.3 mm in diameter and 6–8 mm thick, were 96% dense. In the present study, PbTiO3 ceramics with excess lead (Pb:Ti = 1.1:1.0) had large grains, averaging 14.3 μm. Lower-lead ceramics (Pb:Ti = 1.0:1.0 and 0.9:1.0) had smaller grains, averaging 1.8 μm. The PbTiO3 ceramics with a high lead content cracked during sintering at 1150°C, whereas the other ceramics did not crack. Excess lead, in a more-than-stoichiometric ratio, promoted grain growth and caused disintegration of the ceramics. Therefore, uncracked PbTiO3 ceramics apparently can be fabricated by avoiding excess lead, possibly because restricted grain growth in low-lead ceramics causes low residual stress over many small grains during transition. The electrical properties measured in the present study for PbTiO3 ceramics with a Pb:Ti ratio of 1:1 are d 33= 35 pC/N, K 3= 64, k p= 0.59, and k t≈ 0.  相似文献   

2.
Dense BaTiO3 ceramics consisting of submicrometer grains were prepared using the spark plasma sintering (SPS) method. Hydrothermally prepared BaTiO3 (0.1 and 0.5 µm) was used as starting powders. The powders were densified to more than similar/congruent95% of the theoretical X-ray density by the SPS process. The average grain size of the SPS pellets was less than similar/congruent1 µm, even by sintering at 1000-1200°C, because of the short sintering period (5 min). Cubic-phase BaTiO3 coexisted with tetragonal BaTiO3 at room temperature in the SPS pellets, even when well-defined tetragonal-phase BaTiO3 powder was sintered at 1100° and 1200°C and annealed at 1000°C, signifying that the SPS process is effective for stabilizing metastable cubic phase. The measured permittivity was similar/congruent7000 at 1 kHz at room temperature for samples sintered at 1100°C and showed almost no dependence on frequency within similar/congruent100-106 Hz; the permittivity at 1 MHz was 95% of that at 1 kHz.  相似文献   

3.
Nano-sized TiO2 powders were prepared by controlled hydrolysis of TiCl4 and Ti(O-i-C3H7)4 solutions and nitrided in flowing NH3 gas at 700°–1000°C to form TiN. Nano-sized TiN was densified by spark plasma sintering at 1300°–1600°C to produce TiN ceramics with a relative density of 98% at 1600°C. The microstructure of the etched ceramic surface was observed by SEM, which revealed the formation of uniformly sized 1–2 μm grains in the TiCl4-derived product and 10–20 μm in the Ti(O-i-C3H7)4-derived TiN. The electric resisitivity and Vickers micro-hardness of the TiN ceramics was also measured.  相似文献   

4.
Silicon nitride ceramics were prepared by spark plasma sintering (SPS) at temperatures of 1450°–1600°C for 3–12 min, using α-Si3N4 powders as raw materials and MgSiN2 as sintering additives. Almost full density of the sample was achieved after sintering at 1450°C for 6 min, while there was about 80 wt%α-Si3N4 phase left in the sintered material. α-Si3N4 was completely transformed to β-Si3N4 after sintering at 1500°C for 12 min. The thermal conductivity of sintered materials increased with increasing sintering temperature or holding time. Thermal conductivity of 100 W·(m·K)−1 was achieved after sintering at 1600°C for 12 min. The results imply that SPS is an effective and fast method to fabricate β-Si3N4 ceramics with high thermal conductivity when appropriate additives are used.  相似文献   

5.
Lead-based ferroelectric (FE) ceramics exhibit superior electromechanical properties; therefore, there has been an increased focus on developing new lead-based FE materials with high Curie temperature ( T c) and enhanced properties. The aim of this study was to investigate new compositions in the Pb(Mg1/3Nb2/3)O3–Pb(Yb1/2Nb1/2)O3–PbTiO3 ( PMN–PYbN–PT) system to enhance the electromechanical properties while increasing the T c and lowering the sintering temperature. The 0.575[0.5PMN–0.5PYbN]–0.425PT composition at PMN/PYbN (50/50) mole ratio were prepared by reactive sintering PMNT and PYbNT powder mixtures at 950°–1200°C for 4 h. PMNT and PYbNT powders were calcined via the columbite method. Samples were prepared by cold isostatic pressing at 80 MPa. Dense and fully perovskite 0.575[0.5PMN–0.5PYbN]–0.425PT ceramics were fabricated at 975°C for 4 h, and these samples displayed a remnant polarization ( P r) of 32 μ C/cm2, coercive field ( E c) of 17 kV/cm, and a piezoelectric charge coefficient ( d 33) of 475 pC/N. It is proposed that this ternary system can be tailored for various applications.  相似文献   

6.
PbTiO3 sputtering targets 8 cm in diameter were prepared using spark-plasma sintering (SPS) for relatively short periods, ∼2 min. Submicrometer-sized PbTiO3 powders with a relatively large size distribution were densified to ∼86% of the theoretical X-ray density using the SPS process. In contrast, large-sized (8 cm in diameter) ceramics could not be prepared from starting powders with a relatively narrow particle-size distribution. Formation of cracks in the large PbTiO3 targets was observed when samples were prepared under higher pressures (>50 MPa) or at higher temperatures (>900°C). Crack formation was attributed to unrelaxed internal stress originating from lower pore contents and from an inhomogeneous distribution of cations in the ceramics prepared under these conditions.  相似文献   

7.
Microstructure characteristics, phase transition, and electrical properties of (Na0.535K0.485)0.926Li0.074(Nb0.942Ta0.058)O3 (NKN-LT) lead-free piezoelectric ceramics prepared by normal sintering are investigated with an emphasis on the influence of sintering temperature. Some abnormal coarse grains of 20–30 μm in diameter are formed in a matrix consisting of about 2 μm fine grains when the sintering temperature was relatively low (980°C). However, only normally grown grains were observed when the sintering temperature was increased to 1020°C. On the other hand, orthorhombic and tetragonal phases coexisted in the ceramics sintered at 980°–1000°C, whereas the tetragonal phase becomes dominant when sintered above 1020°C. For the ceramics sintered at 1000°C, the piezoelectric constant d 33 is enhanced to 276 pC/N, which is a high value for the Li- and Ta-modified (Na,K)NbO3 ceramics system. The other piezoelectric and ferroelectric properties are as follows: planar electromechanical coupling factor k p=46.2%, thickness electromechanical coupling factor k t=36%, mechanical quality factor Q m=18, remnant polarization P r=21.1 μC/cm2, and coercive field E c=1.85 kV/mm.  相似文献   

8.
The effect of spark plasma sintering (SPS) on the densification behavior of Pb(Mg1/3Nb2/3)O3–PbTiO3 ceramics has been investigated. Specimens with a density of >99% of the theoretical density (TD) were obtained using SPS treatment at 900°C. Through normal sintering at 1200°C, however, the density of the specimen was only ∼92% of TD.  相似文献   

9.
Single-crystal layers of 0.65Pb(Mg1/3Nb2/3)O3·0.35PbTiO3 (PMN-35PT) were grown heteroepitaxially on {001}-BaTiO3 template crystals. A {001}-BaTiO3 crystal was embedded in a fine-grained matrix of PMN-35PT containing excess PbO and heated between 950° and 1150°C for 0–5 h. The initial growth of the PMN-35PT on the {001} surface and the growth of the matrix grains both displayed a t 1/3 dependence which is characteristic of diffusion-controlled growth. Growth was limited to ∼100–150 μm due to the significantly reduced driving force at longer times because of matrix coarsening and porosity evolution.  相似文献   

10.
Ba1– x Pb x TiO3 powder with a fixed composition was prepared by the reaction of BaTiO3 powders with molten PbCl2at various PbCl2/BaTiO3 molar ratios at 600° and 800°C in a nitrogen atmosphere. When 0.1 μm powder was used, the reaction was finished when x = 0.9. Two phases of BaTiO3and a solid solution of Ba1– x Pb x TiO3 coexisted, but the final phase gave a solid solution of Ba1– x Pb x TiO3 at 800°C. When 0.5 μm powder was used, the two phases coexisted in the products at 600°C at PbCl2/BaTiO3= 1.0. A sintered compact of Ba1– x Pb x TiO3 powders solid solution was prepared by hot isostatic pressing, and its dielectric constant was measured in the temperature range 20°–550°C.  相似文献   

11.
The densification behavior of ZrO2 (+ 3 mol% Y2O3)/85 wt% Al2O3 powder compacts, prepared by the hydrolysis of metal chlorides, can be characterized by a transition- and an α-alumina densification stage. The sintering behavior is strongly determined by the densification of the transition alumina aggregates. Intra-aggregate porosity, resulting from calcination at 800°C, partly persists during sintering and alumina phase transformation and negatively influences further macroscopic densification. Calcination at 1200°C, however, densifies the transition alumina aggregates prior to sintering and enables densification to almost full density (96%) within 2 h at 1450°C, thus obtaining a microstructure with an alumina and a zirconia grain size of 1 μm and 0.3–0.4 μm, respectively.  相似文献   

12.
Lead-based piezoelectric ceramics typically require sintering temperatures higher than 1000°C at which significant lead loss can occur. Here, we report a double precursor solution coating (PSC) method for fabricating low-temperature sinterable polycrystalline [Pb(Mg1/3Nb2/3)O3]0.63-[PbTiO3]0.37 (PMN–PT) ceramics. In this method, submicrometer crystalline PMN powder was first obtained by dispersing Mg(OH)2-coated Nb2O5 particles in a lead acetate/ethylene glycol solution (first PSC), followed by calcination at 800°C. The crystalline PMN powder was subsequently suspended in a PT precursor solution containing lead acetate and titanium isopropoxide in ethylene glycol to form the PMN–PT precursor powder (second PSC) that could be sintered at a temperature as low as 900°C. The resultant d 33 for samples sintered at 900°, 1000°, and 1100°C for 2 h were 600, 620, and 700 pm/V, respectively, comparable with the known value. We attributed the low sintering temperature to the reactive sintering nature of the present PMN–PT precursor powder. The reaction between the nanosize PT and the submicrometer-size PMN occurred roughly in the same temperature range as the densification, 850°–900°C, thereby significantly accelerating the sintering process. The present PSC technique is very general and should be readily applicable to other multicomponent systems.  相似文献   

13.
A thin film (60 μm thick) of a gadolinium-doped ceria (GDC) electrolyte was prepared by the doctor blade method. This film was laminated with freeze-dried 42 vol% NiO–58 vol% GDC mixed powder and pressed uniaxially or isostatically under a pressure of 294 MPa. This laminate was cosintered at 1100 °–1500 °C in air for 4–12 h. The laminate warped because of the difference in the shrinkage of the electrolyte and electrode during the sintering. A higher shrinkage was measured for the electrode at 1100 °–1200 °C and for the electrolyte at 1300 °–1500 °C. The increase of the thickness of anode was effective in decreasing the warp and in increasing the density of the laminated composite. The maximum electric power density with a SrRuO3 cathode using 3 vol% H2O-containing H2 fuel was 100 mW/cm2 at 600 °C and 380 mW/cm2 at 800 °C, respectively, for the anode-supported GDC electrolyte with 30 μm thickness.  相似文献   

14.
Intermetallic CoAl powder has been prepared via self-propagating high-temperature synthesis (SHS). Dense CoAl materials (99.6% of theoretical) with the combined additions of ZrO2(3Y) and Al2O3 have been fabricated via spark plasma sintering (SPS) for 10 min at 1300°C and 30 MPa. The microstructures are such that tetragonal ZrO2 (0.3 μm) and Al2O3 (0.5 μm) particles are located at the grain boundaries of the CoAl (8.5 μm) matrix. Improved mechanical properties are obtained; especially the fracture toughness and the bending strength of the materials with ZrO2(3Y)/Al2O3= 16/4 mol% are 3.87 MPa·m1/2 and 1080 MPa, respectively, and high strength (>600 MPa) can be retained up to 1000°C.  相似文献   

15.
Spinel platelets were formed from a powder mixture of 3–5 μm wide and 0.2–0.5 μm thick α-Al2O3 and 1–8 μm (average 3 μm) MgSO4 heated 2 h at 1200°C. The hexagonal platelet shape of the original α-Al2O3 platelet was maintained in the spinel, although their size was slightly increased and their surface roughened. When a mixture of α-Al2O3 platelets and MgO powder was heated 3 h at 1400°C, the spinel formed lost the platelet morphology of the alumina.  相似文献   

16.
Spark plasma sintering (SPS) was used to fabricate bismuth titanate (Bi4Ti3O12) ceramics. The densification, microstructure development and dielectric properties were investigated. It was found that the densification process was greatly enhanced during SPS. The sintering temperature was 200°C lower and the microstructure was much finer than that of the pressureless sintered ceramics, and dense compacts with a high density of over 99% were obtained at a wide temperature range of 800°–1100°C. Dielectric property measurement indicated that the volatilization of Bi3+ was greatly restrained during SPS, resulting in an unprecedented low dielectric loss for pure Bi4Ti3O12 ceramics.  相似文献   

17.
A dense Ca(Ti0.75Fe0.25)O3−α (Ca(Ti,Fe)O3) film, which is a mixed conductor of oxide ions and electrons/holes, was prepared on a porous CaTiO3 substrate by a spin-coating method. The calcined Ca(Ti,Fe)O3 powder with 2–3 μm grain sizes was mixed with a dispersant in ethanol to form the slurry for spin coating. A uniform Ca(Ti,Fe)O3 green film was obtained at 1000–1500 rpm on the rotating porous CaTiO3 substrate, which had an average pore diameter of a few micrometers. The optimum sintering conditions for the spin-coated films were a soaking temperature of 1235°C and a holding time of 2 h, in air. A dense, sintered Ca(Ti,Fe)O3 film }20–50 μm thick was prepared by repeating the coatingsintering process. The gas-tight film prepared on the porous substrate exhibited higher electrochemical permeation of oxygen at an operating temperature of 1000°C compared with that of thicker, sintered Ca(Ti,Fe)O3 disks.  相似文献   

18.
(Ni1− x Zn x )Nb2O6, 0≤ x ≤1.0, ceramics with >97% density were prepared by a conventional solid-state reaction, followed by sintering at 1200°–1300°C (depending on the value of x ). The XRD patterns of the sintered samples (0≤ x ≤1.0) revealed single-phase formation with a columbite ( Pbcn ) structure. The unit cell volume slightly increased with increasing Zn content ( x ). All the compositions showed high electrical resistivity (ρdc=1.6±0.3 × 1011Ω·cm). The microwave (4–5 GHz) dielectric properties of (Ni1− x Zn x )Nb2O6 ceramics exhibited a significant dependence on the Zn content and to some extent on the morphology of the grains. As x was increased from 0 to 1, the average grain size monotonically increased from 7.6 to 21.2 μm and the microwave dielectric constant (ɛ'r) increased from 23.6 to 26.1, while the quality factors ( Q u× f ) increased from 18 900 to 103 730 GHz and the temperature coefficient of resonant frequency (τf) increased from −62 to −73 ppm/°C. In the present work, we report the highest observed values of Q u× f =103 730 GHz, and ɛ'r=26.1 for the ZnNb2O6-sintered ceramics.  相似文献   

19.
Porous mullite (3Al2O3·2SiO2) ceramics with an open porosity up to 92.9% were fabricated by a gel freeze-drying process. An alumina (Al2O3) gel mixed with ultrafine silica (SiO2) was frozen and sublimation of ice crystals was carried out by drying the frozen body under a low pressure. Porous mullite ceramics were prepared in air at 1400°–1600°C due to the mullitization between Al2O3 and SiO2. A complex and porous microstructure was formed, where large dentritic pores with a pore size of ∼100 μm contained small cellular pores of 1–10 μm on their internal walls. Owing to the complete mullitization, a relatively high-compressive strength of 1.52 MPa was obtained at an open porosity of 88.6%.  相似文献   

20.
CrN powder consisting of granular particles of ∼3 μm has been prepared by self-propagating high-temperature synthesis under a nitrogen pressure of 12 MPa using Cr metal. Dense pure CrN ceramics and CrN/ZrO2(2Y) composites in the CrN-rich region have been fabricated by hot isostatic pressing for 2 h at 1300°C and 196 MPa. The former ceramics have a fracture toughness ( K IC) of 3.3 MPa ·m1/2 and a bending strength (σb) of 400 MPa. In the latter materials almost all of the ZrO2(2Y) grains (0.36–0.41 μm) are located in the grain boundaries of CrN (∼4.6 μm). The values of K IC (6.1 MPa · m1/2) and σb (1070 MPa) are obtained in the composites containing 50 vol% ZrO2(2Y).  相似文献   

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