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1.
We report on the correlation between structural, ferroelectric, piezoelectric and dielectric properties of the (1-x)Ba0.7Ca0.3TiO3-xBaTi0.8Zr0.2O3 (x?=?0.45, 0.55; abbreviated as 55BCT30 and 45BCT30) ceramics close to morphotropic phase boundary (MPB) region. The 55BCT30 and 45BCT30 ceramics were synthesized by the standard, high-temperature solid state ceramic method. X-ray diffraction (XRD) along with Rietveld refinement indicate that the 55BCT30 ceramics exhibit rhombohedral (R, space group R3m), orthorhombic (O, space group Amm2) and tetragonal (T, space group P4mm) phases while 45BCT30 ceramics exhibit only T and O phases. The temperature dependent Raman spectroscopy measurements confirm the structure and phase transformations observed from XRD. All the ceramics are chemically homogeneous and exhibit a dense microstructure with a grain size of 5–7?µm. The presence of polarization-electric field and strain-electric field hysteresis loops confirm the ferroelectric and piezoelectric nature of the ceramics. The polarization current density-electric field curves show the presence of two sharp peaks in opposite directions indicating the presence of two stable states with opposite polarity. Higher values of direct piezoelectric coefficient (d33 ~?360 pC/N) were observed due to the existence of low energy barrier near MPB region and polymorphism. The 55BCT30 ceramics exhibit a higher value of electrostrictive coefficient (Q33 ~?0.1339?m4/C2) compared to the well-known lead-based materials. The temperature dependent dielectric measurements indicate the O to T phase transition for 55BCT30 and 45BCT30. These ceramics exhibit a Curie temperature (Tc) of 380?K with a dielectric maximum of ~ 4500.  相似文献   

2.
This study examined the effects of samarium and erbium co-doping on the structural, optical, and electrical properties of ceria (CeO2). Ceramic (Ce0.8Sm0.2-xErxO2-δ; x?=?0, 0.05, 0.10, 0.15, 0.20) electrolytes were synthesized via sol-gel assisted citric acid–nitrate combustion and calcined at 850?°C for 5?h. The calcined electrolytes possessed a cubic fluorite crystal structure without impure phases. The direct band gap of the calcined electrolytes increased as the erbium content increased and the lowest band gap was obtained for Ce0.8Sm0.2O2-δ (SDC) electrolyte. The calcined electrolyte powders were subsequently pressed into cylindrical pellets by uniaxial die pressing, and the pellets were sintered at 1400?°C for 5?h. The sintered densities of the pellets were measured with Archimedes’ method. The relative density of Ce0.8Sm0.1Er0.1O2-δ co-doped ceria electrolyte was higher than those of singly doped ones, and these findings were further confirmed through field emission scanning electron microscopy. Electrochemical impedance spectroscopy indicated that the conductivity of erbium-doped ceria increased as the samarium content increased. The maximum total ionic conductivity was observed in Ce0.8Sm0.1Er0.1O2-δ co-doped electrolyte. However, the singly doped SDC electrolyte exhibited the highest ionic conductivity of 13.12 mS/cm and the lowest activation energy of 0.580?eV at 600?°C among all other Ce0.8Sm0.2-xErxO2-δ co-doped ceria electrolytes.  相似文献   

3.
Effect of BiFeO3 (BFO) content on the microstructure and electrical properties of BaTi0.9Zr0.1O3 (BTZ) ceramics prepared by the solid-state reaction technique was investigated. X-ray diffraction analyses show that BFO diffused into the lattice of BTZ to form a solid solution with perovskite structure. The relative density of the BTZ ceramics is increased by the introduction of BFO. The dielectric study reveals that the dielectric constant and the average dielectric loss of the solid solution decreased simultaneously with an increase in BFO content. The materials undergo a diffuse type ferroelectric phase transition. The diffusivity increases with increase in BFO contents in the studied composition range. On the other hand, the piezoelectric coefficient and electromechanical coupling coefficient decrease simultaneously with increasing the BFO content, whereas the mechanical quality factor increases gradually. The structure–property relationship and the mechanism associated with the change of the electrical properties are discussed intensively.  相似文献   

4.
Novel (1–x)(0.94Bi0.5Na0.5TiO3–0.06BaTiO3)–xSr0.7La0.2TiO3 ternary lead-free ceramics (BNBT–xSL, x?=?0.00–0.08) were fabricated by the widely used solid-state sintering technique. The crystal phase, microstructure, dielectric relaxation, piezoelectric, and electromechanical properties of each composition were systematically analyzed. It is found that the addition of SL has little effect on the crystal phase and grain morphology, but it can remarkably improved the relaxation property of the ceramic sample and gave rise to favourable dielectric properties in a wide range of temperatures. In addition, as the SL content increases, the ferroelectric to relaxor temperature (TF-R) is adjusted to below ambient temperature. More importantly, the decay of ferroelectric phase resulted in a significant increase in strain value: the large strain of 0.5% with normalized strain of 625?pm/V was obtained at 80kv/cm and x?=?0.04. Finally, the composition exhibited high strain of temperature insensitivity range from room temperature to 100?°C, the strain value remained above 0.4% and kept within 5%. The results are due to the coexistence of rhombohedral polar-nanoregions (PNRs) and tetragonal PNRs during the relaxor region. This result is of great importance to the developments of temperature-insensitive strain sensors and actuators.  相似文献   

5.
In order to ascertain the structural relationship of zirconolite and pyrochlore for their potential application in HLW immobilization, the Gd-doped zirconolite-pyrochlore composite ceramics (Ca1-xZr1-xGd2xTi2O7) were systematically synthesized with x?=?0.0–1.0 by traditional solid-phase reaction method. The phase evolution and microstructure of the as-prepared samples have been elucidated by XRD and Rietveld refinement, Raman spectroscopy, BSE-EDS and HRTEM analysis. The results showed that zirconolite-2M, zirconolite-4M, perovskite and pyrochlore, four phases were identified in Ca1-xZr1-xGd2xTi2O7 system and could be coexisted at x?=?0.4 composition. With the increase of Gd3+ substitution, the phase evolution was followed by zirconolite-2M→zirconolite-4M→pyrochlore. It is illustrated that the phase transformation from zirconolite-2M to zirconolite-4M was promoted by the preferential substitution of Gd3+ for Ca2+. And the solubility of Gd3+ in zirconolite-2M, zirconolite-4M and pyrochlore increased in sequence. The chemical stability test was also measured by the PCT leaching method. The normalized elemental release rates of Ca, Zr, Ti and Gd in Ca1-xZr1-xGd2xTi2O7 system were fairly low and in the range of 10?6?10?8 g?m?2 d?1, which indicated a potential ceramics composite ensemble of CaZrTi2O7-Gd2Ti2O7 system for nuclear HLW immobilization.  相似文献   

6.
Nano-sized Ba1−xLaxTiO3 (0.00 ≤ x ≤ 0.14) powders were prepared by a coprecipitation method and calcined at 850 °C in air. The corresponding ceramics were obtained by Spark Plasma Sintering (SPS) at 1050 °C. These ceramics are oxygen deficient and are marked as Ba1−xLaxTiO3−δ. Both powders and ceramics were characterized by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). The effect of lanthanum concentration on the densification behavior, on the structure and the microstructure of the oxides was investigated. Average grain sizes are comprised between 54 (3) nm and 27 (2) nm for powders, and 330 (11) nm and 36 (1) nm for ceramics according to the La-doping level. Powders crystallize in the cubic (or pseudo-cubic) perovskite phase. The structure of ceramics consists in a mixture of cubic (or pseudo-cubic) and tetragonal perovskite type phases. As the lanthanum content increases, the tetragonality of the samples decreases, as well as the grain size.  相似文献   

7.
(Ba1?xRx)(Ti1?xHox)O3 (R = La, Pr, Nd, Sm; x ≥ 0.04) (BRTH) ceramics were prepared using a mixed oxides method. The solubility limits in BRTH with R = La, Pr, Nd, Sm were determined by XRD to be x = 0.11, 0.12, 0.06, and 0.14, respectively. The ionic radius of R at Ti-site plays a decisive role in the solubility limit in BRTH. Only BRTH with R = La satisfied Vegard's law. The multiplicity of photoluminescence (PL) signals of Nd3+/Ho3+ and Sm3+/Ho3+ in Raman scattering under 532-nm excitation laser and the high-permittivity abnormality for the denser BRTH with R = Sm and at x = 0.07 were reported. The PL provided the evidence of a small number of Ho3+ at Ba-site in BRTH and it was determined that the number of Ba-site Ho3+ ions increased from 0.05 at% at R = La to 0.19 at% at R = Sm with increasing atomic number of light rare earth. BRTH exhibited a much broadened dielectric-temperature characteristics, marked by ×5 T, ×6 T, ×7 T, and ×8 S dielectric specifications for BRTH with R = La, Pr, Nd, Sm and at x = 0.06, respectively, and they exhibited lower dielectric loss (tan δ < 0.015) at room temperature. The dielectric-peak temperature (Tm) of BRTH decreased linearly at a rate of less than ?21 °C/%(R/Ho). The defect chemistry, solubility limit, lower dielectric loss, and dielectric abnormality are discussed.  相似文献   

8.
Li4Ti5O12 (Fd-3m space group) materials were synthesized by controlling the lithium and titanium ratios (Li/Ti) in the range of 0.800-0.900 by using a spray-drying method, followed by calcination at several temperatures between 700 and 900 °C for large-scale production. Chemical and structure studies of the final products were done by X-ray diffraction (XRD), neutron diffraction (ND), X-ray photon electron spectroscopy (XPS), scanning electron microscopy (SEM) and inductively coupled plasma mass spectrometry (ICP-MS). The optimum synthesis condition was examined in relation to the electrochemical characteristics including charge-discharge cycling and ac impedance spectroscopy. It was found that when the spray-drying precursors at the Li/Ti ratio of 0.860 were calcined at 700-900 °C for 12 h in air, a pure Li4+xTi5−xO12−δ (x = 0.06-0.08) phase with a lithium-excess composition was obtained. Based on the structural studies, it was found that the excess lithium is located at the lithium and titanium layer of the 16d site in the spinel structure (Fd-3m). These pure Li4+xTi5−xO12−δ (x = 0.06-0.08) phase materials showed a higher discharge capacity of ∼164 mAh g−1 at 1.55 V (vs. Li/Li+), between the cut-off voltage of 1.2-3.0, with an excellent cyclability and superior rate performance in comparison with the Li4Ti5O12 phase containing impurity phases.  相似文献   

9.
Evolution of the microstructure, optical, and magnetic properties have been investigated systematically in multiferroic CuFe1-xSnxO2 (x?=?0–0.05) ceramics. Substitution of Sn4+ for Fe3+ results in expansion of CuFeO2 lattice, and reduces the density of the material, but the metal oxidation states are unchanged. Observation of the optical properties shows that the value of the direct optical band gap (Eg) decreases with increasing Sn doping level, and that the CuFe1-xSnxO2 (x?=?0–0.04) series with values >?3.1?eV. Magnetic susceptibility measurements show that Sn4+ doping decreases the Curie-Weiss temperature, i.e. weakens the strength of the antiferromagnetic interaction between high-spin Fe3+ ions, but does not affect the stability of the antiferromagnetic phase, and all samples undergo successive magnetic transitions at about TN1 =?15?K and TN2 =?11?K. However, magnetization curves show that changes occur in the magnetic interactions and both ferromagnetism and antiferromagnetism co-exist in the Sn4+-doped samples. The maximum value of the saturation magnetization of 1.8?emu·g?1 was observed for the x?=?0.03 sample in a 2.5?kOe field. The changes in the magnetic behavior are closely related to the lattice distortion and charge compensation, which are discussed in detail in this work.  相似文献   

10.
采用固相法合成(La0.2Sm0.2Nd0.2Y0.2Er0.2)2Zr2O7陶瓷材料,并使用XRD、SEM、热膨胀仪和激光导热仪对其物相、形貌、热膨胀性能和热导率进行测试和分析。结果表明:(La0.2Sm0.2Nd0.2Y0.2Er0.2)2Zr2O7陶瓷材料表现为单一的烧绿石结构,晶粒致密,晶界清晰且有较高的致密度,平均热膨胀系数为1.138×10-5 K-1,1 000℃时热导率为2.14 W·m-1·K-1。  相似文献   

11.
This study reports the successful preparation of single-phase perovskite (Ba0.5Sr0.5)0.8La0.2Fe1−xMnxO3−δ (x = 0-0.2) by the citrate-EDTA complexing method. The crystal structure, thermal gravity analysis, coefficient of thermal expansion, electrical conductivity, and electrochemical performance of (Ba0.5Sr0.5)0.8La0.2Fe1−xMnxO3−δ were investigated to determine its suitability as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The lattice parameter a of (Ba0.5Sr0.5)0.8La0.2Fe1−xMnxO3−δ decreases as the amount of Mn doping increases. The coefficients of thermal expansion of the samples are in the range of 21.6-25.9 × 10−6 K−1 and show an abnormal expansion at around 400 °C associated with the loss of lattice oxygen. The electrical conductivity of the (Ba0.5Sr0.5)0.8La0.2Fe1−xMnxO3−δ samples decreases as the amount of Mn-doping increases. The electrical conductivity of the samples reaches a maximum value at around 400 °C and then decreases as the temperature increases. The charge transfer resistance, diffusion resistance and total resistance of a (Ba0.5Sr0.5)0.8La0.2Fe0.8Mn0.15O3-δ-Ce0.8Sm0.2O1.9 composite cathode electrode at 800 °C are 0.11 Ω cm2, 0.24 Ω cm2 and 0.35 Ω cm2, respectively.  相似文献   

12.
Novel high temperature ceramic capacitors (1??x)(Na0.5Bi0.5TiO3 ??0.15Ba0.8Ca0.2Ti0.8Zr0.2O3)??xK0.5Na0.5NbO3 were synthesized in the solid-state reaction route. The influence of K0.5Na0.5NbO3 modification on dielectric behavior, energy-storage properties, ac impedance and temperature stable dielectric performance were systematically investigated. The reduced grain size and enhanced relaxor properties are obtained with the addition of KNN. The content of x?=?0.1 exhibits a stable permittivity (~ 1630) and dielectric loss (<?0.05) over a relatively broad temperature range (66–230?°C). A variation in permittivity within ±?15% can be observed over a pretty wide temperature range of 66–450?°C. Beyond that, this ceramic shows enhanced energy-storage properties with the density (Wrec) of 0.52?J/cm3 and efficiency (η) of 80.3% at 110?kV/cm. The possible contributions of the grain and the grain boundary to the ceramic capacitance are discussed by the ac impedance spectroscopy.  相似文献   

13.
In this paper effects of Ca and Mg substitution on oxygen sensing properties of hot spot based Eu123 rods are reported. Eu1−xCaxBa2Cu3O7−δ (x=0.2–0.5) and Eu1−yMgyBa2Cu3O7−δ (y=0.2–0.5) ceramics were synthesized from oxide powders using the standard solid state method and fabricated into short rods. For Ca-substituted rods, after appearance of a visible hot spot, a constant current plateau in IV curve was formed. The output current response of the rod in periodically changing pO2 between 20% and 100% showed improved stability and reproducibility for x=0.4 compared to x=0.2. Improved oxygen absorption and desorption time was observed for x=0.4 compared to previously reported unsubstituted rod. On the other hand, for Mg-substituted rods the IV behavior after formation of hot spot showed a negative slope. Faster absorption time of 3.0 s and desorption time of 6.9 s were observed for y=0.4 compared to y=0.2. The improved output current stability, reproducibility and response time is suggested to be due to changes in oxygen activation energy and increased hole concentration as a result of Ca2+/Mg2+substitutions. The Mg-substituted rods showed better performance compared to Ca-substituted rods possibly due to higher porosity and vacancy concentration.  相似文献   

14.
Composites having general formula 0.1Ni0.8Zn0.2Fe2O4–0.9Pb1−3x/2SmxZr0.65Ti0.35O3 with x=0, 0.01, 0.02 and 0.03 were synthesized by a conventional solid state reaction route. X-ray diffraction analysis was carried out to confirm the coexistence of individual phases and microstructural study was done by using a scanning electron microscope. Dielectric properties were studied as a function of temperature and frequency. To study ferroelectric and magnetic ordering in composite samples, PE and MH hysteresis loops were recorded respectively. Maximum magnetoelectric coupling coefficient of 22.5 mV/cm Oe was observed for sample with x=0.03. A significant improvement in dielectric, ferroelectric, piezoelectric and magnetoelectric properties was observed for Sm substitution.  相似文献   

15.
Single-phase superfine refractory oxides of composition La2?xGdxZr2O7 (x = 0, 0.5, 1, 1.5, 2) have been synthesized using glycol-citrate route. Dependencies of degree of dispersion and phase composition on chemical composition for such oxides were determined. Fluorite-pyrochlore transition observed during thermal treatment of these oxides was examined. It was stated that this transition occurred in the temperature range 1000–1200?°C for all formulations with exception of gadolinium zirconate Gd2Zr2O7 which kept the fluorite structure even after long-term exposure (4?h) at a temperature of 1400?°С. Samples of corresponding ceramics which density amount to 95–98% of the theoretical value were obtained using FAST/SPS process. Coefficients of linear thermal expansion (CLTE) of manufactured materials were measured. It was found that CLTE values for all samples except for gadolinium zirconate were independent of temperature in the range 400–1000?°C. It was shown that Gd2Zr2O7 kept the fluorite structure under conditions of FAST/SPS process at a temperature of 1600?°C.  相似文献   

16.
The value of critical current density at 77 K in “zero” applied field (Jc) characterizing the superconducting state for YBa2Cu3O7−δ ceramics is closely related to the microstructure.The interrelationships between the microstructural factors such as pore volume fraction, oxygen content, average grain size, are complex. However, these factors also influence the normal state resistivity measured at room temperature (ρ300). We demonstrate how the current carrying cross section influences Jc and ρ300 in a similar way. Data, reported for two classes of YBa2Cu3O7−δ: small grain porous ceramics and larger-grain denser ceramics, reveal an approximate linear relation between ρ300 K and Jc. Extrapolation of this relation to a fully dense small grain YBa2Cu3O7−δ ceramic yields values of ρ300 = 0.4 mΩ cm and Jc = 103 A cm−2.  相似文献   

17.
A series of Mn1.5−xCo1.5NixO4 (0≤x≤1.2) negative temperature coefficient materials was synthesized by the sol–gel method. The optimal pH of reaction solutions was obtained by theoretical calculation. XRD and X-ray intensity ratios (I220/I440) and (I440/I422) studies showed that as-sintered ceramics are single spinel structures with different cation distributions. The Ni2+ ions not only enter B-site but also occupy A-site. Electrical studies showed that with increasing Ni content, the resistivity decreased from 909.229 Ω cm to 221.873 Ω cm initially in the range of x≤0.5 and then increased to 726.933 Ω cm when x=1.2, whereas the B value decreased from 4427 K to 2134 K. In addition, different sintering temperature ceramics were investigated. A higher sintering temperature results in lower resistivity and B value at same Ni content. The Mn1.0Co1.5Ni0.5O4 material showed much improved electrical stability at 125 °C for 1000 h. The rate of change (ΔR/R) is 0.2%.  相似文献   

18.
The performance of the LaBaCuFeO5+δ-Ce0.8Sm0.2O1.9 (LBCF-SDC) composite cathodes was studied in this paper. Electrical conductivity, thermal expansion and electrochemical properties were investigated by four probing DC technique, dilatometry, AC impedance and polarization techniques, respectively. The thermal expansion coefficients of the LBCF-SDC were between (16.3 and 13.4) × 10−6 K−1 from 30 to 850 °C, which was lower value than LBCF (17.0 × 10−6 K−1). AC Impedance spectroscopy measurements of LBCF-SDC/SDC/LBCF-SDC test cell were carried out. Polarization resistance values for the LBCF-SDC10 cathode was as low as 0.097 Ω cm2 at 750 °C.  相似文献   

19.
MgO containing vanadate glasses of composition V2-xMgxO5-δ (x?=?0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) have been prepared successfully by melt-quench technique. The structural properties of the as-quenched samples are explored with the help of X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. Thermal properties and conductivity of the samples are investigated using differential thermal analysis (DTA) and impedance spectroscopy, respectively. Density, inter-ionic distance, and fragility index are found to decrease with the addition of MgO content. Higher content of MgO improves the glass formation tendency and reduces the thermal stability of the samples. The conductivity of the V2-xMgxO5-δ samples decreases as the MgO concentration increases due to hindrance in the polaronic conduction of vanadium ions. The conductivity of the samples decreases to ? 10?4 S?m?1 for x?=?0.30 at 300?°C, while activation energy increases to 0.38?eV. These samples may find application in solid state batteries and fuel cells due to their higher conductivity.  相似文献   

20.
Haitao Gu 《Electrochimica acta》2009,54(27):7094-9945
The electrochemical properties of LaBaCo2O5+δ-xSm0.2Ce0.8O1.9 (LBCO-xSDC, x = 20, 30, 40, 50, 60, wt%) were investigated for the potential application in intermediate-temperature solid oxide fuel cells (IT-SOFCs). The LBCO-50SDC composite cathode exhibited the best electrochemical performance in the LBCO-xSDC cathodes. With x = 50 wt%, the ASR was 1.308 Ω cm2 at 500 °C (0.267 Ω cm2 at 600 °C and 0.052 Ω cm2 at 700 °C). The maximum of exchange current density i0 was 0.5630 A cm−2 at 700 °C. The improved electrochemical properties of LBCO-50SDC were ascribed to the porous structures of the cathode and more cathode/electrolyte/gas triple phase boundary (TPB) areas.  相似文献   

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