共查询到20条相似文献,搜索用时 15 毫秒
1.
Wei Zhao Heping Zhou Yongke Yan Dan Liu 《Journal of the American Ceramic Society》2008,91(4):1322-1325
Plate-like Na0.5 Bi0.5 TiO3 (NBT) particles with perovskite structure were synthesized by topochemical microcrystal conversion from plate-like particles of layer-structured Na0.5 Bi4.5 Ti4 O15 (NBIT) at 950°C in NaCl molten salt. As the precursors of NBT, plate-like NBIT particles were first synthesized by molten salt process by the reaction of Bi4 Ti3 O12 , Na2 CO3 , and TiO2 . After the topochemical reactions, layer-structured NBIT particles were transformed to the perovskite NBT platelets. NBT particles with a thickness of approximately 0.5 μm and a length of 10–15 μm retained the morphology feature of the precursor. High-aspect-ratio NBT platelets are suitable templates to obtain textured ceramics (especially NBT-based ceramics) by (reactive) template grain growth process. 相似文献
2.
J. T. Zeng K. W. Kwok W. K. Tam H. Y. Tian X. P. Jiang H. L. W. Chan 《Journal of the American Ceramic Society》2006,89(12):3850-3853
Large plate-like Na0.5 Bi0.5 TiO3 (NBT) templates have been successfully synthesized from bismuth layer-structured ferroelectric Na0.5 Bi4.5 Ti4 O15 (NBIT) particles by the topochemical method. Because of the highly anisotropic structure, plate-like NBIT particles were first synthesized by the molten-salt process. After the topochemical reaction with the complementary reactants (Na2 CO3 , and TiO2 ) in NaCl flux, the layer-structured NBIT particles were transformed to the perovskite NBT templates. The resulting NBT templates are large and of plate-like shape. Our results also reveal that they are more effective in inducing grain orientation in the BNKT-BT ceramics as compared with BIT templates. For a BNKT-BT ceramic textured with 20 wt% of NBT templates, it exhibits a very high degree of grain orientation and gives a large Lotgering factor of 0.89. 相似文献
3.
Jakob König Botjan Janar Danilo Suvorov 《Journal of the American Ceramic Society》2007,90(11):3621-3627
X-ray diffraction analyses and scanning electron microscopy revealed that Na0.5 Bi0.5 TiO3 (NBT) and NaTaO3 (NTa) form solid solutions across the whole concentration range. With increasing NTa content the symmetry of the solid solutions gradually changed from rhombohedral, on the NBT-rich side, to orthorhombic, on the NTa-rich side. No morphotropic phase boundary was found between these phases. With increasing NTa content, the perovskite lattice parameter ( a p ) and the sintering temperature increase, whereas the grain size decreases. In the case of pure NTa, ceramics with a secondary phase were obtained, identified as Na2 Ta8 O21 , which was formed during the sintering process. A study of the dielectric properties showed that with an increasing concentration of NTa, there was a reduction and broadening of the permittivity maximum, a reduction of the temperatures of the dielectric anomalies, and a reduction of the dielectric losses. 相似文献
4.
Yuanhua Lin Ce-Wen Nan Jianfei Wang Gang Liu Junbo Wu Ning Cai 《Journal of the American Ceramic Society》2004,87(4):742-745
The dielectric properties of Na0.5 Bi0.5 TiO3 (NBT) -based composites incorporating silver particles prepared by sintering at a low temperature of ∼900°C are reported. The dielectric constant increases with the amount of metal silver particles in the measured frequency range (150 Hz to 1 MHz), and could be enhanced up to ∼20 times higher than that of pure NBT ceramics, which was ascribed to the effective electric fields developed between the dispersed particles in the matrix and the percolation effect. Further investigation revealed that the dielectric constant of the composites has weak frequency and temperature dependence (−50°C to +50°C). 相似文献
5.
Mankang Zhu Liying Liu Yudong Hou Hao Wang Hui Yan 《Journal of the American Ceramic Society》2007,90(1):120-124
Microstructure and electrical properties of manganese oxide (MnO)-doped (Na0.5 Bi0.5 )0.92 Ba0.08 TiO3 (NBBT) piezoceramics were investigated in this work. X-ray diffraction analysis shows that the suitable substitution of Mn ion into the B site induces the lattice distortion of perovskite NBBT: the solution limit is at 0.3 wt% MnO. Besides, it is observed that the sintering properties can be improved by adding a small amount of MnO, thus increasing the grain size and the relative density. Further, the temperature dependence of the dielectric permittivity of NBBT ceramics indicates that the MnO addition reconstructs the disorder array destroyed by joining BaTiO3 in the Na0.5 Bi0.5 TiO3 system due to the sizable radius of the B-site cations. Combining these effects of MnO addition, the optimal electrical properties were acquired for NBBT ceramic with addition of 0.30 wt% MnO. The excellent electrical properties of MnO-doped NBBT ceramics indicate its promising application in large displacement actuators. 相似文献
6.
Sodium bismuth titanates Na1/2 Bi1/2 TiO3 (NBT) doped with 0–3 wt% Er2 O3 were prepared by the conventional solid-state reaction method. The X-ray diffraction results revealed that the sintered Er-doped NBT ceramics exhibited a pure perovskite structure with Er3+ concentrations ranging from 0 to 1 wt%. At a low Er2 O3 concentration, the Er-doped NBT ceramics showed enhanced electrical properties with dielectric constant ɛ33 T /ɛ0 =636, a low dielectric dissipation factor (tan δ=3.3%), a low coercive field ( E c =4.56 kV/mm), and a high piezoelectric constant ( d 33 =75 pC/N). The relationship between the composition and properties of Er-doped NBT ceramics has been discussed. 相似文献
7.
The sintering and electrical characteristics of La-modified Na1/2 Bi1/2 TiO3 (NBT) was investigated from a defect structure viewpoint. To reveal the role of cation vacancies, two series of ceramics, with different cation vacancies, were processed to compensate the excess positive charge of lanthanum ions. In a region of complete solid solution, the grain size of NBLT-B {[(Na0.5 Bi0.5 )1− x La x ]Ti1−0.25 x O3 } was smaller than that of NBLT-A {[(Na0.5 Bi0.5 )1−1.5 x La x ]TiO3 } and densification was enhanced more effectively in NBLT-B. With the aid of thermoelectric power, electric conductivity, and electrotransport measurements, it was found that different sintering behaviors between NBLT-A and NBLT-B specimens were related to the change in the type of cation vacancies present and that lanthanum ion–cation vacancy pairs played an important role in reducing the grain growth and enhancing the densification process. 相似文献
8.
Yu-Dong Hou Lei Hou Ting-Ting Zhang Man-Kang Zhu Hao Wang Hui Yan 《Journal of the American Ceramic Society》2007,90(6):1738-1743
The sol–gel–hydrothermal processing of (Na0.8 K0.2 )0.5 Bi0.5 TiO3 (NKBT) nanowires as well as their densification behavior were investigated. The morphology and structure analyses indicated that the sol–gel–hydrothermal route led to the formation of phase-pure perovskite NKBT nanowires with diameters of 50–80 nm and lengths of 1.5–2 μm, and the processing temperature was as low as 160°C, but the conventional sol–gel route tended to lead to the formation of NKBT agglomerated porous structured nanopowders, and the processing temperature was higher than 650°C. It is believed that the gel precursor and hydrothermal environment play an important role in the formation of the nanowires at a low temperature. Owing to the better packing efficiency and therefore a good sinterability of the freestanding nanowhiskers, the pressed pellets made by NKBT nanowires showed >98% theoretical density at 1100°C for 2 h. The sol–gel–hydrothermal-derived ceramics have typical characteristics of relaxor ferroelectrics, and the piezoelectric properties were better than the ceramics prepared by the conventional sol–gel and solid-state reaction. 相似文献
9.
Matja Spreitzer Botjan Janar Danilo Suvorov 《International Journal of Applied Ceramic Technology》2009,6(2):302-311
The phase relations and the mechanism of solid-state synthesis for the Na0.5 Bi0.5 TiO3 –Li3 x La(2/3)− x □(1/3)−2 x TiO3 system were investigated using X-ray powder diffraction, scanning electron microscopy, and thermal analysis. The study revealed that the extent of the homogeneity range—which is related to the A-site substitution between (Na0.5 Bi0.5 )2+ and (Li3 x La(2/3)− x □(1/3)−2 x )2+ pseudo cations of a perovskite structure—depends strongly on the ordering of the (Li3 x La(2/3)− x □(1/3)−2 x )2+ species. The solid-state reaction of the compounds in the homogeneity range is completed only after multiple high-temperature firings. However, the system is also subjected to a slow thermal decomposition; this is particularly so for the compounds with a high × value and an increased Li3 x La(2/3)− x □(1/3)−2 x TiO3 concentration. 相似文献
10.
Haibo Zhang Shenglin Jiang Koji Kajiyoshi 《Journal of the American Ceramic Society》2009,92(9):2147-2150
MnO-doped 0.82Bi0.5 Na0.5 TiO3 –0.18Bi0.5 K0.5 TiO3 (NBT–KBT) thick films with thickness about 40 μm have been prepared using screen printing on Pt electroded alumina substrates. The strong pyroelectric coefficient of 3.8 × 10−4 C·(m2 ·°C)–1 was observed in 1.0 mol% MnO-doped-thick films, and the calculated detectivity figure of merit as high as 1.1 × 10−5 Pa−0.5 , which can be comparable to that of the commonly used lead based materials. The enhancement of the pyroelectric performances is attributed to the reductions in dielectric constant and loss and the improvements in the pyroelectric coefficient, which can be ascribed to the Mn acts as a hard dopant in the NBT–KBT lattice, creating oxygen vacancies and pinning the residual domains. 相似文献
11.
PbTiO3 -doped sodium bismuth titanate (Na1/2 Bi1/2 )1− x Pb x TiO3 of perovskite structure is one of the best-known piezoelectrics/ferroelectrics. However, it has not been properly investigated in any thin-film forms. In this study, the dielectric properties of (Na1/2 Bi1/2 )0.87 Pb0.13 TiO3 thin films synthesized via a sol–gel route were investigated. They exhibit a strong frequency dispersion of the dielectric permittivity at relatively high frequencies, which is shifted to lower frequencies with increasing temperature. The electrical behavior can be fitted using Jonscher's universal law for dielectric relaxation. The peculiar dielectric behaviors observed can be ascribed to the coexistence of two different dielectric phases in the films, which is believed to be associated with the growth of the local Pb2+ TiO3 nanoclusters upon substitution of Pb2+ for Na+ /Bi3+ in the (Na1/2 Bi1/2 )1− x Pb x TiO3 films. 相似文献
12.
The phases formed in the ternary system (Na1/2 Bi1/2 )TiO3 –Bi4 Ti3 O12 –BaTiO3 (NBT–BTO–BT) were studied at 1150°C in air. A very accurate picture of the ternary phase diagram was obtained examining almost 90 different compositions, exploiting low-angle XRD analyses to study the layer compounds. New compounds with five perovskite blocks ( m =5) were discovered deep in the phase diagram. No compounds with m >5 were found. It was also established that pure perovskite compounds can be obtained only at compositions very close to the NBT–BT line. The relationships between the phases is discussed and it is hypothesized that the number of perovskite blocks in the system is determined by charged sites being created by the progressive substitution of Bi3+ in the A site of the perovskite blocks of BTO with the A cations of the perovskite end-member. 相似文献
13.
Subsolidus phase relations in the system Na2 O-Bi2 O3 -TiO2 at 1000°C were investigated by solid-state reaction techniques and X-ray diffraction methods. Five ternary compounds were observed in the system: Na0.5 Bi4.5 Ti4 O15 ; Na0.5 Bi0.5 TiO3 ; a cubic pyrochlore solid solution composed of xNa2 O.25Bi2 O3 .(75−;x) TiO2 where x is 2.5 to 3.75; a new compound Na0.5 Bi8.5 Ti7 O27 indexed with the orthorhombic cell of a = 5.45, b = 5.42, and c = 36.8 Å; and an unidentified phase with the probable composition NaBiTi6 O14 . 相似文献
14.
Shi Chen Mengjia Wu Liqiong An Yongxiang Li Shiwei Wang 《Journal of the American Ceramic Society》2007,90(2):664-666
Upconversion emission properties of Na1/2 Bi1/2 TiO3 :Er3+ ceramics prepared by the solid-state reaction method were analyzed as a function of Er3+ concentration and incident pump power. Strong green (550 nm) and red (670 nm) emission bands were observed with 980 nm excitation at room temperature. Experimental results showed that the emission bands can be tuned by changing Er3+ concentration. Upconversion processes in these samples result from not only a two-photon excited-state absorption process but also a nonradiative energy transfer and cross-relaxation process. 相似文献
15.
Hwi-Yeol Park Cheol-Woo Ahn Kyung-Hoon Cho Sahn Nahm Hyeung-Gyu Lee Hyung-Won Kang Duk-Hee Kim Kyeong-Soon Park 《Journal of the American Ceramic Society》2007,90(12):4066-4069
The sintering temperature of 0.95(Na0.5 K0.5 )NbO3 –0.05BaTiO3 (NKN–BT) ceramics needs to be decreased below 1000°C to prevent Na2 O evaporation, which can cause difficulties in poling and may eventually degrade their piezoelectric properties. NKN–BT ceramics containing CuO were well sintered at 950°C with grain growth. Poling was easy for all specimens. Densification and grain growth were explained by the formation of a liquid phase. The addition of CuO improved the piezoelectric properties by increasing the grain size and density. High piezoelectric properties of d 33 =230 pC/N, k p =37%, and ɛ3 T /ɛ0 =1150 were obtained from the specimen containing 1.0 mol% of CuO synthesized by the conventional solid-state method. 相似文献
16.
Kyung-Hoon Cho Hwi-Yeol Park Cheol-Woo Ahn Sahn Nahm Kenji Uchino Seung-Ho Park Hyeung-Gyu Lee Hwack-Joo Lee 《Journal of the American Ceramic Society》2007,90(6):1946-1949
The 0.95(Na0.5 K0.5 )NbO3 –0.05SrTiO3 (0.95NKN–0.05ST) ceramics formed in this study had a porous microstructure with small grains and low piezoelectric properties due to their low density. However, when a small amount of Na2 O was intentionally subtracted from the 0.95NKN–0.05ST ceramics, a liquid phase was formed, which led to increased density and grain size. Piezoelectric properties were also improved for the Na2 O-subtracted 0.95NKN–0.05ST ceramics. The increased density and grain size were responsible for the enhancement of the piezoelectric properties. In particular, the 0.95(Na0.49 K0.5 )NbO2.995 –0.05ST ceramics showed high piezoelectric properties of d 33 =220, k p =0.4, Q m =72, and ɛ3 T /ɛo =1447, thereby demonstrating their promising potential as a candidate material for application to lead-free piezoelectric ceramics. 相似文献
17.
"Reactive-templated grain growth" (RTGG) processing of Bi1/2 Na1/2 TiO3 (BNT)-based ceramics is reported. Molten salt synthesis was used to prepare platelike (∼0.2 μm × 5 μm × 5 μm) Ruddlesden–Popper (Sr3 Ti2 O7 (ST)) and Aurivillius (BaBi2 Nb2 O9 (BBN)) phases which were used as "templates" in studies of RTGG with BNT-based matrixes. A "citrate-gel" route was designed to produce intimately mixed, fine-grain matrixes for these studies. The analytical techniques used were powder X-ray diffraction and microstructural examination of dry-pressed and fired compacts. For mixtures templated with BBN, single-phase perovskite readily formed, and an initially heterogeneous microstructure evolved toward a dense assemblage of anisometric, micrometer-scale grains. Perovskite formation was more sluggish in the mixtures templated with ST, and the final sintered microstructure featured larger, porous grains in an equiaxed, micrometer-scale matrix. A qualitative model, which examined the excess constituents in the matrix after formation of stoichiometric ABO3 perovskite, is proposed to explain the observations. The model predicted an excess of Na2 O and TiO2 in the matrix in the case of BBN templates and only excess TiO2 in the case of ST templates. The results indicate that careful examination of matrix and template chemistry could be important in the selection of systems for RTGG processing. 相似文献
18.
Microstructure development in Bi0.5 (Na0.5 K0.5 )0.5 TiO3 prepared by a reactive-templated grain growth process was dependent on the sizes of platelike Bi4 Ti3 O12 (BiT) and equiaxed TiO2 particles used as starting materials. Calcined compacts were composed of large, platelike template grains and small, equiaxed matrix grains, the sizes of which were determined by those of the BiT and TiO2 particles, respectively. Texture was developed by the growth of template grains at the expense of matrix grains during sintering, and a new mechanism of grain growth was proposed on the basis of microstructure observation. The grain growth rate was determined by the template and matrix grain sizes, and a dense ceramic with extensive texture was obtained using small BiT and TiO2 particles. 相似文献
19.
Xueyi Sun Jun Chen Ranbo Yu Ce Sun Guirong Liu Xianran Xing Lijie Qiao 《Journal of the American Ceramic Society》2009,92(1):130-132
Lead-free potassium sodium niobate-based piezoelectric ceramics (1− x )(Na0.5 K0.5 )NbO3 – x BiScO3 (KNN–BS) ( x =0∼0.05) have been prepared by an ordinary sintering process. Single perovskite phase of KNN–BS exhibits an orthorhombic symmetry at x <0.015 and pseudocubic symmetry at x >0.02, separating by a MPB at 0.015≤ x ≤0.02. Piezoelectric and ferroelectric properties are significantly enhanced in the MPB, which are as follows: piezoelectric constant d 33 =203 pC/N, planar coupling coefficient k p =0.36, remnant polarization P r =24.4 μC/cm2 . These solid solution ceramics look promising as a potential lead-free candidate materials. 相似文献
20.
Pornsuda Bomlai Pattraporn Wichianrat Supasarute Muensit Steven J. Milne 《Journal of the American Ceramic Society》2007,90(5):1650-1655
Sodium-potassium niobate [Na0.5 K0.5 NbO3 ] powders were prepared following the conventional mixed oxide method. An orthorhombic XRD pattern, consistent with single-phase Na0.5 K0.5 NbO3 , was obtained after calcination at 900°C for 6 h. Introducing 5 mol% excess Na2 CO3 and K2 CO3 into the starting mixture allowed milder calcination conditions to be used, for example 800°C for 2 h. Primary particles in 5 mol% excess samples were cuboid, with maximum sizes of ∼2.5 μm. Equiaxed 0.3–0.4-μm particles were formed for non-excess powders, and also for powders prepared with 1 and 3 mol% excess alkali carbonates. The results suggest liquid formation during calcination of the excess 5-mol% starting powders. 相似文献