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1.
In the course of searching environmental friendly lead-free relaxor ferroelectrics a complete phase diagram of barium zirconate titanate, Ba(Zr x Ti1− x )O3 system with compositions 0.00≤ x ≤1.00 has been developed based on their dielectric behavior. It has been shown that BaZr x Ti1− x O3 system depending on the composition, successively depicts the properties extending from simple dielectric (pure BaZrO3 ) to polar cluster dielectric, relaxor ferroelectric, second order like diffuse phase transition, ferroelectric with pinched phase transitions and then to a proper ferroelectric (pure BaTiO3 ). A comprehensive structure–property correlation of BaZr x Ti1− x O3 ceramics has been studied to understand the various ferroelectric phenomena in the whole phase diagram. 相似文献
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Hong Xia Yuan Xiang Ming Chen Min Min Mao 《Journal of the American Ceramic Society》2009,92(10):2286-2290
CaNdAlO4 microwave dielectric ceramics were modified by Ca/Ti co-substitution, and their dielectric characteristics were evaluated along with their structure and microstructures. Ca1+ x Nd1− x Al1− x Ti x O4 ( x =0, 0.025, 0.05, 0.10, 0.15, 0.20) ceramics with the relative density of over 95% theoretical density were obtained by sintering at 1400°–1450°C in air for 3 h, where the K2 NiF4 -type solid solution single phase was determined from the compositions of x <0.20, while a small amount of CaTiO3 secondary phase was detected for x =0.20. With Ca/Ti co-substitution in CaNdAlO4 ceramics, the dielectric constant (ɛr ) increased with increasing x , and the temperature coefficient of resonant frequency (τf ) was adjusted from negative to positive, while the Q × f 0 value increased significantly at first and reached an extreme value at x =0.025 and the maximum at x =0.15. The best combination of microwave dielectric characteristics were achieved at x =0.15 (ɛr =19.5, Q × f 0 =93 400 GHz, τf =−2 ppm/°C). The improvement of the Q × f 0 value primarily originated from the reduced interlayer polarization with Ca/Ti co-substitution, while the decreased tolerance factor, the subsequent increased interlayer stress, and the appearance of CaTiO3 secondary phase brought negative effects upon the Q × f 0 value. 相似文献
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Mari Lou Balmer Fred F. Lange Carlos G. Levi 《Journal of the American Ceramic Society》1994,77(8):2069-2075
Aqueous solutions of zirconium acetate and aluminum nitrate were spray pyrolyzed at 250°C and upquenched to different temperatures to yield metastable solid solutions of composition Zr(1− x ) Alx O(2− x /2) . An amorphous oxide forms first during pyrolysis which subsequently crystallizes as a single phase for x ≤ 0.57 (≤40 mol% Al2 O3 ). The crystallization temperature increased with Al2 O3 content. Electron diffraction, supported by Raman spectroscopy, indicates that the initial phase is tetragonal. At higher temperatures, the initial solid solation partitions to other metastable phases, viz., t -ZrO2 +γ-Al2 O3 , prior to achieving their equilibrium phase assemblage, m -ZrO2 +α-Al2 O3 . Partitioning yields a nanocomposite microstructure with grain sizes of 20–100 nm, compared to the 3 to 5 nm in the initial, single phase. Compositions containing 45 to 50 mol% Al2 O3 concurrently crystallize and partition. The structure selected during crystallization and the partitioning phenomena are discussed in terms of diffusional constraints during crystallization, which are conceptually similar to those operating during rapid solidification. 相似文献
5.
Piezoelectric ceramics Na1− x Ba x Nb1− x Ti x O3 with low BaTiO3 concentrations x have been prepared by the solid-state reaction method, and their ferroelectric and piezoelectric properties have been studied. The ceramics are classic ferroelectrics when x ≤0.10, and the ferroelectric–paraelectric phase transition becomes diffusive when x ≥0.15. A low doping level of BaTiO3 changes the NaNbO3 ceramics from antiferroelectric to ferroelectric. With the increase in BaTiO3 doping level, the Curie temperature of ceramics decreases linearly and the remnant polarization and coercive field also decrease, while their dielectric constant increases. Na0.9 Ba0.1 Nb0.9 Ti0.1 O3 ceramics show the largest piezoelectric constant d 33 (147 pC/N) and good sinterability, suggesting that it is a good candidate for lead-free piezoelectric ceramics. 相似文献
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The superplastic behavior of YBa2 Cu3 O7− x ceramic superconductors was studied. Large compressive deformation over 100% strain was measured in the temperature range of 775°–875°C, with a strain rate of 1 × 10−5 to 1 × 10−3 /s, and a grain size of 0.5–1.4 μm. The nature of the deformation was investigated in terms of three deformation parameters: the stress exponent ( n ), the grain size exponent ( p ), and the activation energy ( Q ). The measured values of these parameters were n = 2 ± 0.3, p = 2.7 ± 0.7, and Q = 745 ± 100 kJ/mol. With the aid of the deformation map, the deformation mechanism was identified as grain boundary sliding accommodated by grain boundary diffusion. The conclusion is consistent with the microstructural observations made by SEM and TEM: the invariance of equiaxed grain shape, the absence of significant dislocation activity, no grain boundary second phases, and no significant texture development. 相似文献
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Radostin Stefanov Pavlov Juan B. Carda Castelló Vicente Blasco Marzá J. M. Hohembergerger 《Journal of the American Ceramic Society》2002,85(5):1197-1202
New high-stability red-shade ceramic pigments based on pyrochlore solid solutions Y2 Sn2− x Cr x O7−δ ( x = 0–1, 0 < δ= 0–1/2 x ) were developed employing conventional solid-state reaction synthesis. The relationship between their optical properties and microstructure was analyzed by X-ray diffractometry and ultraviolet–visible-light spectroscopy. Decomposition of the structure with formation of the perovskite YCrO3 observed for chromium substitutions x ≥ 5 was attributed mainly to high concentration of defects. The structural and optical parameters of the materials were found to correlate with the concentration of a species with higher oxidation state than Cr(III), such as Cr(IV) or Cr(V). 相似文献
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The (YBa2 Cu3 )1−x Nax O7–δ system in the range of x = 0–0.8 was investigated. Experimental data suggest that the sodium doping with x 0.26 does not affect the critical transition temperature Tc , and the crystal structure maintains the orthorhombic lattice with a slightly smaller unit cell. However, sodium doping increases the sintering and grain growth kinetics, resulting in a higher superconducting phase volume and an enhanced Meissner effect. It also lowers the processing temperaturel. The experimental data also suggest that the sodium atoms diffuse into the superconducting YBa2 Cu3 O7−δ crystallites, which stabilizes the orthorhombic phase. The transition temperature (ortho-rhombic to tetragonal) in sodium-doped materials increases with the increasing concentration of sodium. 相似文献
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The cubic-tetragonal (c-t) phase equilibria in the system ZrO2 -YO1.5 are thermodynamically analyzed from Landau's phenomenological theory. The calculated c-t two-phase field is depicted as a miscibility gap with a sharp maximum and the spinodal region as originally predicted by Hillert and Sakuma. However, the observed c-t two-phase field and the spinodal region are better described by the present model. In addition, this model can be used to discuss the nature of the c-t diffusionless transformation from the order parameter in contrast with the original model. The predicted change in the tetragonality of t-ZrO2 with YO1.5 content is slightly different from that in the c/a axial ratio estimated from X-ray diffraction analysis. The displacement of cations and anions may not take place simultaneously during the c-t transformation. 相似文献
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Karen M. Cruickshank Xiping Jing Graeme Wood Eric E. Lachowski Anthony R. West 《Journal of the American Ceramic Society》1996,79(6):1605-1610
A solid-solution phase with the general formula Ba6-3x Nd8+2x Ti18 O54 , where 0.25(5) ≤×≤ 0.75(5), has been characterized at 1250°C; this phase has been variously described as BaNd2 Ti4 O12 and BaNd2 Ti5 O14 in the literature. Variation in its stoichiometry is accommodated via the cation substitution mechanism, 3Ba2 ⇆2Nd3+ . The location and extent of the solid solution were demonstrated by a combination of phase diagram studies and X-ray diffraction techniques, including lattice parameter measurements and electron microscopy. A combination of techniques was employed due to the insensitivity of secondary phase detection by X-ray diffraction in this system. Using this approach, a second possible solid-solution mechanism, Ba2+ 2Nd3+ ⇆2Ti4+ , is discounted. 相似文献
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Hiroaki Takeda Masataka Ohgaki Takashi Kizuki Kazuaki Hashimoto Yoshitomo Toda Shigekazu Udagawa Kimihiro Yamashita 《Journal of the American Ceramic Society》2000,83(11):2884-2886
The formation process of Ba2 La8 (SiO4 )6 O2 was clarified using thermogravimetry–differential thermal analysis (TG-DTA) and a high-temperature powder X-ray diffraction (HT-XRD) method. Phase changes identified from the HT-XRD data surprisingly corresponded to the weight loss and/or endothermic peaks observed in the TG-DTA curves. Raw material with the composition Ba2 La8 (SiO4 )6 O2 was completely reacted at 1400°C and produced only an apatite-type compound without a secondary phase. Moreover, the synthesis of Ba2+ x La8− x (SiO4 )6 O2−δ crystals with x = 0–2 was attempted using a solid-state reaction. 相似文献
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The solid-state reaction of SrNb2 O6 and BaNb2 O6 to form Sr x Ba1− x Nb2 O6 (SBN) at different temperatures and heating rates was investigated. The reaction kinetics were analyzed by X-ray diffractometry for quenched samples, and the internal-standard method was applied to quantify the extent of the reaction. A nonisothermal kinetic empirical model was proposed to evaluate the activation energy and rate constant of SBN with different Sr:Ba ratios. It was found that the kinetic form would change above and below a transition at a reaction fraction of ∼60%, which might be due to the change of the frequency factor. It was also verified that the model that was presented was more favorable to describe the nonisothermal reaction kinetics of SBN. 相似文献
14.
Michiyuki Yoshida Yutaka Shinoda Takashi Akatsu Fumihiro Wakai 《Journal of the American Ceramic Society》2002,85(11):2834-2836
Ultrafine-grained monoclinic ZrO2 polycrystals (MZP) and 3-mol%-Y2 O3 -stabilized tetragonal ZrO2 polycrystals (3Y-TZP) were obtained by hot isostatic pressing (HIP). Both MZP and TZP were "high-purity" materials with impurities less than 0.1 wt%. The deformation behavior was studied at 1373 K, which was lower than the monoclinic ↔ tetragonal transition temperature. The stress exponent of 3Y-TZP with grain size of 63 nm was 3 in the higher stress region, and increased from 3 to 4 with decreasing stress. The deformation of MZP was characterized by a stress exponent of 2.5 over a wide stress range. The strain rate of 3Y-TZP was slower than that of MZP by 1 order of magnitude. It was suggested that either the doped yttrium or the difference in the crystal structure affected the diffusion coefficients of ZrO2 . 相似文献
15.
Electrical properties of CeO2 thin films of different Y2 O3 dopant concentration as prepared earlier were studied using impedance spectroscopy. The ionic conductivities of the films were found to be dominated by grain boundaries of high conductivity as compared with that of the bulk ceramic of the same dopant concentration sintered at 1500°C. The film grain-boundary conductivities were investigated with regard to grain size, grain-boundary impurity segregation, space charge at grain boundaries, and grain-boundary microstructures. Because of the large grain boundary and surface area in thin films, the impurity concentration is insufficient to form a continuous highly resistive Si-rich glassy phase at grain boundaries, such that the resistivity associated with space-charge layers becomes important. The grain-boundary resistance may originate from oxygen-vacancy-trapping near grain boundaries from space-charge layers. High-resolution transmission electron microscopy coupled with a trans-boundary profile of electron energy loss spectroscopy gives strong credence to the space-charged layers. Since the conductivities of the films were observed to be independent of crystallographic texture, the interface misorientation contribution to the grain-boundary resistance is considered to be negligible with respect to those of the impurity layer and space-charge layers. 相似文献
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Yoshiyuki Abe Kazuyuki Kakegawa Yoshinori Sasaki 《Journal of the American Ceramic Society》1992,75(1):234-236
A complex perovskite of Sr(Cu x Zn1- x )1/2 W1/2 O3 (SCZW) is synthesized by a new combination of wet and dry processess. Mixed oxides containing Cu2+ and Zn2+ (CZ) are prepared by the wet process (coprecipitate method). SCZW is obtained by the dry process (mixed-oxide method) from a mixture of CZ, SrCO3 , and WO3 . SCZW has practically no compositional, unlike solid solutions prepared by the conventional dry method. The wet–dry process method is useful because the wet process is applied to only B-site cations having the same valence. 相似文献
17.
Our analysis of the microwave dielectric properties of the δ-Bi2 O3 –Nb2 O5 solid solution (δ-BNss ) showed a continuous increase in permittivity and dielectric losses with an increasing concentration of Nb2 O5 . The only discontinuity was found for the temperature coefficient of resonant frequency, which is negative throughout the entire homogeneity range but reaches a minimum value for the sample with 20 mol% Nb2 O5 . At the same composition there is a discontinuity in the grain size of the δ-BNss ceramics. For the sample containing 25 mol% Nb2 O5 two structural modifications were observed. A single-phase tetragonal Bi3 NbO7 , in the literature referred to as a Type-III phase, is formed in a very narrow temperature range from 850° to 880°C. A synthesis performed below or above this temperature range resulted in the formation of the end member of the δ-BNss homogeneity range. Compared with the δ-BNss the Bi3 NbO7 ceramics exhibit lower microwave dielectric losses, an increased conductivity, and a positive temperature coefficient of resonant frequency. 相似文献
18.
Om Parkash Hari Shanker Tewari Lakshman Pandey Ravindra Kumar Devendra Kumar 《Journal of the American Ceramic Society》1989,72(8):1520-1522
Attempts have been made to synthesize the compositions with x = 0.01, 0.05, 0.10, 0.20, 0.30, 0.40, and 0.50 in the valence-compensated solid-solution Ba1–x Lax Ti1–x Nix O3 by ceramic methods. Solid solutions formed in the compositions with x0.10. The structure of the composition with x = 0.01 is tetragonal, whereas samples with x = 0.05 and 0.10 are cubic. A ferroelectric-paraelectric transition is observed only in the composition with x = 0.01 at ∼ 350 K. 相似文献
19.
Sandeep Butee Ajit Kulkarni Om Prakash Ramnath P.R.C. Aiyar Sumesh George Mailadi Sebastian 《Journal of the American Ceramic Society》2009,92(5):1047-1053
(Ni1− x Zn x )Nb2 O6 , 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 × 1011 Ω·cm). The microwave (4–5 GHz) dielectric properties of (Ni1− x Zn x )Nb2 O6 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 ZnNb2 O6 -sintered ceramics. 相似文献
20.
Samples of Sr2 Fe2− x Mo x O6 were prepared by solid-state reaction in air and 5%H2 –95%N2 . X-ray diffractometry was used to identify the phases and evaluate the lattice parameters. It is found that molybdenum ions can dissolve in the SrFeO3 even if the sample is heated in air but the solubility is limited. The solubility can be enhanced by heating the sample in low oxygen partial pressure, which is attributed to the larger ionic radii of Fe3+ and Mo5+ than that of Fe4+ . The degradation of Sr2 Fe2− x Mo x O6 in water and air is also reported. 相似文献