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This work presents a study of Na0.5Bi0.5TiO3 (NBT) by transmission electron microscopy in the 20-370 °C temperature range. A new orthorhombic intermediate phase between the rhombohedral and the tetragonal phases is proposed to account for the occurrence of (oee) superstructure spots. The phase transition from the rhombohedral to the orthorhombic phase occurs via a modulated phase formed by rhombohedral blocks and orthorhombic sheets. It is shown that these latter represent rhombohedral (0 1 0) twin planes. The modulated phase is proposed to explain the antiferroelectric and relaxor behaviors of NBT. 相似文献
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N. D. Scarisoreanu F. Craciun A. Chis R. Birjega A. Moldovan C. Galassi M. Dinescu 《Applied Physics A: Materials Science & Processing》2010,101(4):747-751
Na0.5Bi0.5TiO3-BaTiO3 (NBT-BT) thin films grown by pulsed laser deposition have been investigated by X-ray diffraction, scanning electron microscopy,
and dielectric spectroscopy in order to clarify the role of substrate temperature on crystalline structure, grain morphology,
and dielectric properties. We have shown that the structural and dielectric properties of NBT-BT thin films with composition
at morphotropic phase boundary (6% BT) critically depend on the substrate temperature: small variations of this parameter
induce structural changes, shifting the morphotropic phase boundary toward tetragonal or rhombohedral side. Higher deposition
temperature (1000 K) favor the formation of rhombohedral phase, films deposited at 923 K and 973 K have tetragonal symmetry
at room temperature. Grains morphology depends also on the deposition temperature. Atomic force micrographs show grains with
square or rectangular shape in a compact structure for films grown at lower temperatures, while grains with triangular shape
in a porous structure are observed for films grown at 1000 K. Dielectric spectroscopy measurements evidenced the phase transition
between ferroelectric and antiferroelectric phase at 370 K. Films grown at 1000 K shown low electrical resistivity due to
their porous structure. High dielectric constant values (about 800 at room temperature and 2700 at 570 K) have been obtained
for films grown at temperatures up to 973 K. 相似文献
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Qin Zhou Changrong Zhou Jun Cheng Changlai Yuan 《Journal of Physics and Chemistry of Solids》2011,72(8):909-913
Lead-free piezoelectric ceramics (1−x)Bi0.5(Na0.82K0.18)0.5TiO3−xNaSbO3 have been prepared by a conventional ceramics technique, and their microstructure and electrical properties have been investigated. The addition of NaSbO3 has no remarkable effect on the crystal structure within the studied doping content; however, an obvious change in microstructure took place. With increase in NaSbO3 content, the temperature from a ferroelectric to antiferroelectric phase transition increases, and the temperature for a transition from antiferroelectric phases to paraelectric phases changes insignificantly. Simultaneously, the temperature range between the rhombohedral phase transition point and the Curie temperature point becomes smaller. The piezoelectric properties significantly increase with increase in NaSbO3 content and the piezoelectric constant and electromechanical coupling factor attain maximum values of d33=160 pC/N and kp=0.333 at x=0.01. The results indicate that (1−x)Bi0.5(Na0.82K0.18)0.5TiO3−xNaSbO3 ceramic is a promising lead-free piezoelectric candidate material. 相似文献
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Lead-free piezoelectric ceramics of (1−x)K0.5Na0.5NbO3-xLiTaO3 (KNN-LT) system have been investigated in this work. X-ray diffraction, Raman spectra measurements, DSC (Differential Scanning Calorimetric), and dielectric constant versus temperature provide direct evidence that the phase transition temperature between tetragonal and orthorhombic shift to lower temperature with the increasing of LT content. The KNN-0.05LT ceramics exhibit the highest high-field d33 up to 220 pm/V. At the same time, we also investigated the relationship between phase structure and electric properties, showing that the orthorhombic phase presents better piezoelectric temperature stabilities than the tetragonal phase. The result may provide a new way for KNN-based lead-free ceramics. 相似文献
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M. D. Durruthy-Rodríguez J. Costa-Marrero M. Hernández-Garcia F. Calderón-Pi?ar Célia Malfatti J. M. Yá?ez-Limón 《Applied Physics A: Materials Science & Processing》2011,103(2):467-476
In this work, visible photoluminescence was observed at room temperature in a sintered Pb(Zr1-xTix)1-y NbyO3\mathrm{Pb}(\mathrm{Zr}_{1-x}\mathrm{Ti}_{x})_{1-y} \mathrm{Nb}_{y}\mathrm{O}_{3} perovskite-type structure system, doped with Nb using the next excitation bands 325, 373 and 457 nm. The intensity and energy
of such emissions have been studied by changing the Nb concentration (0<y<0.01) and the Ti content (x), with x=0.20,0.40,0.53,0.60 and 0.80, on both sides of the morphotropic phase boundary (MPB) zone. The principal bands become visible
at energies of 1.73, 2.56 and 3.35 eV. The results reveal the role of the Nb5+ ion substitutions by Zr4+ or Ti4+ ions and the symmetry presented in the rhombohedral or tetragonal side of the MPB. Raman spectra which are similar for compositions:
20/80, 40/60 and 53/47 (tetragonal phases) show nine bands, centered around 137, 194, 269, 331, 434, 550, 612, 712 and 750
cm−1. The spectra for samples 60/40 and 80/20, rhombohedral phase, show significant differences, only six bands appear, centered
around 124, 209, 234, 330, 549 and 682 cm−1. In addition, optical absorption spectroscopy, structural and micro-structural measurements were carried out by using Uv-vis
spectroscopy, X-ray diffraction and scanning electron microscopy techniques, respectively. The experimental results of band
gap energy, e.g., in our samples are in accordance with the findings by J. Baedi et al. in the calculations of band structure,
energy gap and density of states for different phases of Pb(Zr1−x
Ti
x
)O3 using density functional theory (DFT). 相似文献
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Wenfeng Liang Wenjuan Wu Dingquan Xiao Jvmu Zhu Jianguo Zhu Jiagang Wu 《固体物理学:研究快报》2011,5(7):220-222
0.979K0.5Na0.5Nb1‐xSbx O3‐0.021Bi0.5Na0.5TiO3 (KNNSx ‐BNT) lead‐free piezoelectric ceramics were fabricated by conventional solid state reaction technique, and their phase transition and electrical properties were studied. With the increase of x, the rhombohedral‐orthorhombic phase transition temperature of the ceramics increases. Finally, both the rhombohedral‐orthorhombic and orthorhombic‐tetragonal phase transitions of the ceramics were modified to be around room tempera‐ ture when about 6% Sb were substituted for the Nb site, resulting in the formation of a new phase boundary separating rhombohedral and tetragonal phases. The formation of the new phase boundary results in excellent properties for the ceramics, that is, the KNNS0.05‐BNT ceramic shows an enhancement in piezoelectric properties: d33 = 380 pC/N and kP = 0.438. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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J. Suchanicz V. Bovtun E.M. Dutkiewicz K. Konieczny D. Sitko K. Kluczewska 《Phase Transitions》2016,89(7-8):856-862
ABSTRACTLead-free (Na0.5Bi0.5)1?xSrxTiO3 (x = 0, 0.04 and 0.06) ceramics with relative densities above 97% were prepared by solid-state synthesis process. Their dielectric, thermal and Raman properties were studied. X-ray diffraction analysis shows perovskite structure with rhombohedral symmetry at room temperature. Sr doping of Na0.5Bi0.5TiO3 (NBT) results in an increase of the dielectric permittivity, diffusing of the permittivity maximum and its shift toward lower temperatures. The temperature of the rhombohedral–tetragonal phase transition indicated by the differential scanning calorimetry (DSC) peak and relaxational dielectric anomaly near the depolarization temperature are also shifted toward lower temperatures. The observed increase and broadening of the permittivity maximum, enhancement of the dielectric relaxation near the depolarization temperature, broadening of the DSC anomaly related to the rhombohedral–tetragonal phase transition and broadening of the Raman bands with increasing Sr content are attributed to the increase of the degree of cationic disorder and evident enhancement of the relaxor-like features in NBT–xST. This enhancement could play a positive role in the improvement of the piezoelectric performance of NBT-based ceramics. 相似文献
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《Solid State Ionics》2006,177(19-25):1795-1798
Oxygen deficiency, thermal and chemical expansion of La0.5Sr0.5Fe1−xCoxO3−δ (x = 0, 0.5, 1) have been measured by thermogravimetry, dilatometry and high temperature X-ray diffraction. The rhombohedral perovskite materials transformed to a cubic structure at 350 ± 50 °C. The thermal expansion of the materials up to the onset of thermal reduction was 14–18 × 10− 6 K− 1. Above 500 °C in air (400 °C in N2), chemical expansion contributed to the thermal expansion and the linear thermal expansion coefficients were significantly higher, 16–35 × 10− 6 K− 1. The chemical expansion, εc, showed a maximum of 0.0045 for x = 0.5 and 0.0041 for x = 1 at 800–900 °C. The normalized chemical expansion, εc/Δδ, was 0.036 for x = 0.5 and 0.035 for x = 1 at 800 °C. The chemical expansion can be correlated with an increasing ionic radius of the transition metals with decreasing valence state. 相似文献
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Zhiguo Xia 《Solid State Communications》2007,142(6):323-328
Piezoelectric ceramics with compositions of (0.90−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3-0.10PbZrO3, x=0.28, 0.31, 0.34, 0.37, 0.40 and 0.43, were prepared using the conventional columbite precursor method, and their structural phase transformation and piezoelectric behaviors near the morphotropic phase boundary (MPB) have been systematically investigated as a function of PbTiO3 content. X-ray diffraction (XRD) results demonstrate that the structure of the ceramics experiences a gradual transition process from rhombohedral phase to tetragonal phase with the increasing of PbTiO3 content, and that compositions with x=0.34-0.40 lie in the MPB region of this ternary system. A Raman spectra investigation of the ceramic samples testified to the transformation process of rhombohedral phase to tetragonal phase by comparing the relative intensities of tetragonal E(2TO1) mode and rhombohedral phase Rh mode. The structure information was also correlated to the parabola change of the piezoelectric constant; the maximum piezoelectric constants were obtained near the MPB region. 相似文献
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《Current Applied Physics》2015,15(11):1521-1528
Lead-free piezoelectric ceramics of the composition (1-x)(Bi0.5K0.50)TiO3-xBi(Ni0.50Ti0.50)O3 or (1-x)BKT-xBNiT (when x = 0–0.20 mol fraction) were prepared by a conventional mixed-oxide method and sintered at 1050 °C for 4 h. The effects of BNiT content on the phase equilibria, and the dielectric, ferroelectric and piezoelectric properties were systematically investigated. High density sintered specimens (5.71–6.12 g/cm3) were obtained for all compositions. X-ray diffraction patterns showed that all BKT-BNiT samples exhibited a single perovskite phase which confirms that BNiT and BKT formed a solid solution up to x = 0.20. A morphotropic phase boundary (MPB) separating a BKT-rich tetragonal phase and a BNiT pseudo-cubic phase was identified over the compositional range 0.05 < x < 0.10, where enhanced electrical properties were observed. The optimum dielectric properties (εr = 1710, tanδ = 0.036), ferroelectric properties (Pr = 16.6 μC/cm2, Ec = 22.5 kV/cm and Rsq = 0.86) and piezoelectric properties (d33 = 288 pC/N, Smax = 0.22% and d*33 = 313 pm/V) were observed with a relatively high Tm ∼ 304 °C within this MPB region. Overall, these results indicate that the BKT-BNiT ceramic system is a promising lead-free piezoelectric candidate for further development for actuator applications. 相似文献
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Binyu Zhang Jiagang Wu Xiaopeng Wang Xiaojing Cheng Jianguo Zhu Dingquan Xiao 《Current Applied Physics》2013,13(8):1647-1650
The BaZrO3 and Ta have been used to improve piezoelectric properties of (K, Na)NbO3 ceramics by the construction of the phase boundary, and (1 ? x)K0.48Na0.52(Nb0.95Ta0.05)O3–xBaZrO3 [(1 ? x)KNNT–xBZ] ceramics were prepared by the conventional solid-state method. The effect of BZ content on their phase structure, microstructure, and electrical properties has been investigated. A rhombohedral and orthorhombic phase coexistence has been observed in the compositional range of 0.05 ≤ x ≤ 0.07. With increasing BZ content, their Tc and To–t values decrease gradually, and the dielectric constant increases linearly. The ceramic with x = 0.06 exhibits an enhanced piezoelectric behavior (d33 ~ 193 pC/N and kp ~ 32.6%) because of the coexistence of two phases together with a dense microstructure. As a result, the construction of a rhombohedral and orthorhombic phase boundary is an effective way to improve the piezoelectric properties of KNN-based ceramics. 相似文献
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Phase transition,dielectric and piezoelectric properties of NaNbO3–Bi0.5Li0.5TiO3 lead-free ceramics
Lingling Fu Dunmin Lin Qiaoji Zheng Xiaochun Wu Lang Wu Hailing Sun Yang Wan Ximing Fan Chenggang Xu 《Current Applied Physics》2012,12(6):1523-1528
Lead-free ceramics (1?x)NaNbO3–xBi0.5Li0.5TiO3 have been fabricated by an ordinary sintering technique, and their electric properties and temperature characteristics have been studied. All the ceramics possess a perovskite structure with orthorhombic symmetry, indicating that (Bi0.5Li0.5)TiO3 diffuses into NaNbO3 lattices to form a new solid solution. A low (Bi0.5Li0.5)TiO3 doping level transforms the NaNbO3 ceramics from antiferroelectric to ferroelectric. The ceramics with x ≤ 0.075 are normal ferroelectric, and the ferroelectric-paraelectric phase become diffusives with the doping level of Bi0.5Li0.5TiO3 increasing. As x increases, the Curie temperature of the ceramics decreases linearly, while the relative permittivity εr increases. 0.925NaNbO3–0.075(Bi0.5Li0.5)TiO3 ceramic exhibits the relatively large piezoelectric constant (d33 = 58 pC/N), high Curie temperature (TC = 228 °C) and good temperature stability, suggesting that the ceramics are one of new possible candidates for lead-free piezoelectric materials. 相似文献
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Yih-Chien Chen Yen-Nien Wang Wei-Cheng Lee 《Journal of Physics and Chemistry of Solids》2012,73(2):296-301
The microwave dielectric properties of La1?xSmx(Mg0.5Sn0.5)O3 ceramics were examined with a view to their exploitation for mobile communication. The La1?xSmx(Mg0.5Sn0.5)O3 ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the La0.97Sm0.03(Mg0.5Sn0.5)O3 ceramics revealed no significant variation of phase with sintering temperatures. Apparent density of 6.59 g/cm3, dielectric constant (εr) of 19.9, quality factor (Q×f) of 70,200 GHz, and temperature coefficient of resonant frequency (τf) of ?77 ppm/°C were obtained for La0.97Sm0.03(Mg0.5Sn0.5)O3 ceramics that were sintered at 1500 °C for 4 h. The dielectric constant, and τf of La0.97Sm0.03(Mg0.5Sn0.5)O3 ceramics were almost independent with the sintering temperature as the sintering temperature varied from 1450 to 1600 °C. 相似文献
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PZT基多元系压电陶瓷在三方相含量与四方相含量相等的准同型相界处(MPB)具有极为优异的压电性能。文章采用拉曼散射方法研究了0.5PZN-0.5PZT陶瓷体系中三方-四方相共存与弥散相变现象。研究发现,与纯PZT相比,0.5PZN-0.5PZT体系拉曼谱呈明显宽化特征,表明体系弛豫性较强,依据介温谱计算出弥散因子γ高达1.71。通过对拉曼谱峰进行Gauss函数拟合,定量计算三方相R1模式与四方相E(3TO)和A1(3TO)模式相对强度,以及四方相E(4LO)和A1(3LO)模式与三方相Rh模式相对强度,结果表明0.5PZN-0.5PZT体系三方相与四方相含量相等,组成位于准同型相界,该结果得到XRD相分析验证。电学测量表明0.5PZN-0.5PZT陶瓷压电性能优异:kp=0.66, d33=425 pC/N,适宜作为压电致动器材料使用。 相似文献
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《Solid State Ionics》2006,177(9-10):901-906
Crystal structure, thermal expansion coefficient, electrical conductivity and cathodic polarization of compositions in the system Sm0.5Sr0.5Co1 − xFexO3 − δ with 0 ≤ x ≤ 0.9 were studied as function of Co / Fe ratio and temperature, in air. Two phases, including an Orthorhombic symmetry for 0 ≤ x ≤ 0.4 and a cubic symmetry for 0.5 ≤ x ≤ 0.9, were observed in samples of Sm0.5Sr0.5Co1 − xFexO3 − δ at room temperature. The adjustment of thermal expansion coefficient (TEC) to electrolyte, which is one of the main problems of SSC, could be achieved to lower TEC values with more Fe substitution. High electrical conductivity above 100 S/cm at 800 °C was obtained for all specimens, so they could be good conductors as cathodes of IT-SOFC. The polarization behavior of SSCF as a function of Fe content was evaluated by means of AC impedance using LSGM electrolyte. It was discovered that the Area Specific Resistance (ASR) of SSCF increased as the amount of substitution of Fe for Co increased. When the amount of Fe reached to 0.4, the highest ASR was obtained and then the resistance started decreasing above that. The electrode with a composition of Sm0.5Sr0.5Co0.2Fe0.8O3 − δ showed high catalytic activity for oxygen reduction operating at temperature ranging from 700 to 800 °C. 相似文献
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B. Sitamtze Youmbi Serge Zékeng Samuel Domngang Florent Calvayrac Alain Bulou 《Ionics》2012,18(4):371-377
To date, the fastest lithium ion-conducting solid electrolytes known are the perovskite-type ABO3 oxide, with A = Li, La and B = Ti, lithium lanthanum titanate (LLTO)
Li3x La( 2 \mathord