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1.
《Current Applied Physics》2010,10(4):1059-1061
Lead-free 0.79(Bi0.5Na0.5)TiO3–0.14[Bi0.5(K0.5−xLix)]TiO3–0.07BaTiO3 (BNBK79 + xLi, x = 0.0, 0.1, 0.2, 0.25, 0.3, and 0.4) ceramics were prepared by conventional solid state reaction process. The crystalline structures and surface morphologies are investigated by X-ray diffraction method and scanning electron microscopy. Dielectric and piezoelectric properties were measured. With increasing of lithium substitution, the Curie temperatures of BNBK79 + xLi ceramics increase, but the maximum value of the dielectric constant decreases. And a relatively large remnant polarization of 17.6 μC/cm2 and 157 pC/N of d33 has been obtained when x = 0.3.  相似文献   

2.
Lead-free piezoelectric ceramics of (1?x?y)Bi0.5Na0.5TiO3xBi0.5K0.5TiO3yLiNbO3 (BNT–BKT–LN-x/y) have been fabricated by a conventional solid-state reaction method, and their microstructure and electrical properties have been investigated. The results of X-ray diffraction (XRD) measurement show that K+, Li+ and Nb5+ diffuse into the Bi0.5Na0.5TiO3 lattices to form a solid solution with a pure perovskite structure. The BKT and LN addition has no remarkable effect on the crystal structure. However, a significant change in grain size took place. Simultaneously, with increasing amount of LN, the temperature for a ferroelectric–antiferroelectric phase transition is clearly reduced. The temperature dependence of dielectric properties suggests that the ceramics have diffuse-type phase transition characteristics. The piezoelectric constant d33 and the electromechanical coupling factor kp of the ceramics attain maximum values of 195 pC/N and 0.336 at x=0.18 and y=0.01.  相似文献   

3.
Lead-free ferroelectric ceramics with a morphotropic phase boundary (MPB) composition 85.4% (Bi0.5Na0.5)TiO3–2.6%BaTiO3–12.0% (Bi0.5K0.5)TiO3 (BNT-BT-BKT at a molar ratio of 85.4: 2.6: 12.0) doped with 0.8?mol% Nb2O5 were studied for their crystalline phases and microstructure. The crystalline phases were identified using X-ray diffractometry (XRD) with the contents determined using the Rietveld refinement technique. The phase-transformation-induced microstructure was analyzed using transmission electron microscopy (TEM) and the crystal symmetries were determined using the convergent-beam electron diffraction (CBED) technique. Samples sintered at 1200°C contain a mixture of cubic (C-), tetragonal (T-) and rhombohedral (R-) phases at a ratio of C/T/R?=?56.6: 28.4: 15.0?wt%. Two types of grains are produced: one characterized by a featureless contrast consisting of nano-scale T-domains dispersed in a C-phase matrix; the other a core-shell structure with a shell containing twin and anti-phase-boundary (APB) domains coexisting with a (C?+?T)-phase mixture core. The T- and R-twin boundaries are determined to {111}T and {110}R, respectively, and the fault vector for T-APB to R?=?1/2?110]T. The characteristic microstructure is discussed in terms of the reduction in the point group symmetry and changes in the unit cell volume or the Bravais lattice upon phase transformation among the C-, T- and R-phases. The twin and the APB domains are induced and explained.  相似文献   

4.
5.
《Current Applied Physics》2010,10(2):422-427
New lead-free (Bi1−xyNdxNa1−y)0.5BayTiO3 ceramics were prepared by a conventional ceramic technique and their dielectric and piezoelectric properties were studied. X-ray diffraction studies reveal that Nd3+ and Ba2+ diffuse into the Bi0.5Na0.5TiO3 lattices to form a new solid solution with a pure perovskite structure, and a morphotropic phase boundary (MPB) of rhombohedral and tetragonal phases is formed at 0.04 < y < 0.10. The partial substitutions of Nd3+ and Ba2+ decrease effectively the coercive field Ec and increase significantly the remanent polarization Pr. Because of lower Ec, larger Pr and the formation of the MPB, the piezoelectric properties of the ceramics are significantly enhanced at x/y = 0.02/0.06: d33 = 150 pC/N and kp = 30.5%. The ceramics exhibit relaxor characteristic, which is probably resulted from the cation disordering in the 12-fold coordination sites. The depolarization temperature Td shows a strong compositional dependence and reaches a minimum value at the MPB. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics may contain both the polar and non-polar regions near the depolarization temperature Td, which cause the polarization hysteresis loop become deformed near/above Td.  相似文献   

6.
Pure and homogeneous nanopowders of Ba1? x Sr x TiO3 with compositions x?=?0, 0.10, 0.20, 0.25, 0.30 and 0.35 were prepared by a polymerized complex method based on the Pechini-type reaction route, wherein mixed solutions of citric acid, ethylene glycol, titanium isopropoxide, barium carbonate and strontium carbonate were polymerized to form transparent resins used as precursors for the final oxide powders. X-ray diffraction data indicated the formation of tetragonal BaTiO3 and cubic (Ba,?Sr)TiO3 solid solutions, free from secondary phases. Ceramics with relative densities of 85–93% were obtained after sintering for 3?h at 1300°C and 1350°C, respectively. The Sr content influences the microstructure of the ceramic samples and their ferroelectric characteristics. The P(E) loops are strongly composition-dependent, with reducing the remnant polarization and coercive fields with increasing the Sr addition. The First Order Reversal Curve (FORC) analysis is used for describing the local switching properties and the ac-tunability characteristics. The maximum of the FORC distribution is located at low fields, meaning that small fields are necessary to switch the large majority of the domains of these systems. The tunability determined in the FORC experiment depends not only on the actual field, but also on the reversal field. For two compositions, higher FORC tunability at room temperature was found for the sample closer to its ferro-para phase transition. This result was interpreted in relationship with the domain walls mobility, which is higher for the ferroelectric sample close to its ferro-para phase transition.  相似文献   

7.
Lead-free ceramics (1?x)NaNbO3xBi0.5Li0.5TiO3 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   

8.
A phase diagram for the lead-free ceramics in the (1?x%)(0.89Bi0.5Na0.5TiO3–0.06BaTiO3–0.05K0.5Na0.5NbO3)–x%MnO2 (BNBKN-x%Mn) binary system is constructed for the first time based on the ferroelectric and dielectric measurements. The ferroelectric behaviors under different temperatures suggest that the ceramics are basically of relaxor anti-ferroelectric nature near room temperature. The temperature dependent dielectric properties show that when the addition of MnO2 increases, the relaxor anti-ferroelectric phase can be stabilized to be close to the Curie point, which corresponds to a relaxor anti-ferroelectric to paraelectric phase transition.  相似文献   

9.
ABSTRACT

Lead-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   

10.
ABSTRACT

Thermal expansion, Raman and dielectric properties of the lead-free (1?x)Na0.5Bi0.5TiO3-xSrTiO3 (x = 0, 0.08 and 0.1) ceramic solid solutions, fabricated by the conventional solid-state reaction method, were investigated. The Sr-doping results in an increase of the dielectric permittivity, broadening of the permittivity maximum, enhancement of the relaxation near depolarization temperature, broadening of the Raman bands and shift of all anomalies toward lower temperatures. The observed effects are attributed to an increase of the degree of cationic disorder and enhancement of the relaxor-like features. Anomalies in the thermal expansion strain were observed at the temperatures corresponding to the dielectric anomalies but not related to any phase transitions. These anomalies are supposed to follow changes of the averaged unit cell volume in the temperature interval of tetragonal and rhombohedral phase coexistence.  相似文献   

11.
Lead-free (1?x)[K0.5Na0.5NbO3]?x[LiSbO3] (x=0, 0.04, 0.05 and 0.06)/(KNN-LS) ceramics were prepared by conventional solid-state reaction route (CSSR). For dense morphology pure KNN ceramic was sintered at 1120 °C and LS modified KNN ceramics were sintered at 1080 °C for 4 h, respectively. The structural study at room temperature (RT) revealed the transformation of pure orthorhombic to tetragonal structure with the increase in LS content in KNN-LS ceramics. Temperature dependent dielectric study confirmed the increase of diffuse phase transition nature with the increase in LS content in KNN-LS ceramics. The presence of orthorhombic to tetragonal (TO?T) polymorphic phase transition temperature (PPT) ~43 °C confirmed the presence of two ferroelectric (orthorhombic and tetragonal) phases in 0.95KNN-0.05LS ceramics at RT. 0.95KNN-0.05LS ceramics showed better ferroelectric and piezoelectric properties i.e., remnant polarization (Pr)~18.7 μC/cm2, coercive field (Ec)~11.8 kV/cm, piezoelectric coefficient (d33)~215 pC/N, coupling coefficient (kp)~0.415 and remnant strain ~0.07% were obtained.  相似文献   

12.
《Current Applied Physics》2010,10(6):1367-1371
Lead-free Bi0.5(Na0.78K0.22)0.5TiO3 (BNKT) piezoelectric ceramics were synthesized by the sol–gel technique. The effects of sintering temperatures on the crystal structure, microstructure, densification, dielectric, ferroelectric and electric field-induced strain behaviors of the BNKT ceramics were investigated. X-ray diffraction patterns exhibited a pure perovskite structure from 1075 to 1150 °C. A scanning electron microscopy study revealed an increase in grain size with increasing sintering temperature. The density of the ceramics sintered at 1150 °C reaches a maximum value of 5.55 g/cm3, which is 96% of the theoretical density. BNKT ceramics sintered at an optimum temperature of 1150 °C exhibited a high remnant polarization of 18.5 μC/cm2, a high electric field-induced strain of 0.20% and dynamic piezoelectric coefficient d331 = (Smax/Emax) of 247 pm/V.  相似文献   

13.
Dielectric and piezoelectric properties of (1?x)Ba0.7Sr0.3TiO3?xBa0.7Ca0.3TiO3 (BST?xBCT) (x=0.2–0.9) perovskite ceramics have been investigated. BCT has fully incorporated into BST lattice, forming a complete perovskite solid solution, whose lattice constant χ decreases almost linearly with increase in x from 0.2 to 0.4, while showing an anomalous expansion at 0.4<x≤0.6. This, together with the deviation of tetragonal–orthorhombic phase transition temperature (TOT) from the linear relation TOT (K)=?103.7x+239.3 at x=0.5, suggests that a small amount of Ca2+ has substituted for Ti4+. Curie temperature TC increases linearly with increase in x from 0.2 to 0.9, which is mainly contributed to the increase of the Ba/Sr ratio. The calculated degree of relaxation (γ) is in the range of 1.41–1.53, indicating that the BST–xBCT ceramics are ferroelectric materials with diffuse phase transition. Strain and piezoelectric constant (d33) decrease with increasing x, whereas planar electromechanical coefficient (kp) reaches a maximum (17.0%) at x=0.6.  相似文献   

14.
《中国物理快报》2003,20(2):290-292
We prepared bismuth sodium titanate (Bi0.5Na0.5TiO3)ultrafine powders by the sol-gel method.The dielctric properties of the pressed pellets and fired ceramics with different grain sizes as a function of tempernature at various frequencies were studied.With decreasing grain size,the dielecric anomaly around 200℃ increases,while the dielectric thermal hysteresis decreases,All the samples with grain sizes larger than 100nm show dielectric peaks at temperature of about 350℃.The very little change in Tm observed down to the critical size indicates that Bi0.5Na0.5TiO3 is an order-disorder system above 200℃,In addition,the dielectric peak becomes lower with decreasing grain size and the ferroelectric critical size of Bi0.5Nan0.5TiO3 was eventually determined to be about 100nm according to the disappearance of dielectric peak.  相似文献   

15.
Applied Physics A - Mn-doped 0.948Na0.5Bi0.5TiO3–0.052BaTiO3 (NBBT94.8/5.2) lead-free single crystal with excellent piezoelectric and electromechanical coupling properties was successfully...  相似文献   

16.
The temperature dependence of the real and imaginary parts of dielectric permittivity for (Ba1?xCax)1?3y/2BiyTiO3 solid solution prepared using the solid-state reaction technique, suggests that the relaxor character in this solid solution depends strongly on the Bi than on the Ca doping percent.X-ray diffraction analysis show that Bi doping can be fully incorporated into the perovskite lattice of (Ba1?xCax)TiO3. Doping with Bi causes remarkable shift of the maximum of dielectric permittivity (Tm) at low temperatures and the evolution of εr exhibiting strong frequency dispersion. For some compositions, we have observed a typical behavior of a well-known relaxors. On the other hand, we pointed out that the relaxor character is linked principally to the nature of the substituting element and not to the heterogeneity in general. So the Ca element does not have the same effect as the Bi one.  相似文献   

17.
18.
《Current Applied Physics》2014,14(5):809-813
In this work, 0.96(K0.48Na0.52)1−xLixNbO3–0.04Bi0.5Na0.5ZrO3 lead-free piezoceramics were prepared using the conventional solid state reaction method in order to attain both a high TC and an enhanced d33. The effect of Li content on their phase structure, electrical properties, and stability was systematically investigated. These results indicate that adding Li could result in the increase of TC and the decrease of TO–T. Here we obtain the ceramics with an orthogonal–tetragonal phase boundary in the composition of x = 0.02, and then enhanced piezoelectric properties and a high Curie temperature (i.e., d33 ∼ 255 pC/N, kp ∼ 41%, and TC ∼ 360 °C) were observed, showing the realization of our objective. In addition, a good stability of piezoelectric and ferroelectric properties has been shown in such a material system.  相似文献   

19.
The dielectric and electromechanical characteristics of the (1?x)PMN-xPZT ferroelectric ceramics have been obtained at different temperatures, amplitudes, and frequencies of the measuring field and at different bias field strengths. It is shown that this ferroelectric ceramics at low and infralow frequencies possesses pronounced relaxor properties in a certain temperature range and ferroelectric properties in other temperature range. The temperature and amplitude ranges have been determined, in which the permittivity ?′ either only decreases or first increases and then decreases with an increase in the measuring field amplitude E 0. The temperature ranges of existing the phases similar to the superparaelectric phase, dipole glass phase, and ferroelectric phase are evaluated from the temperature dependences of the coercive field E c (T) and the remanent polarization P r (T) and also from the reverse dependences of ?* and the electromechanical characteristics. The PZT concentration in the PMN-PZT system is determined, at which the electrostrictive constant M 11 is maximum. It is demonstrated that, in the neighborhood of the temperature at a maximum of ?′, the strain S 3 is quadratic in the field E =; that is, S 3=M 11 E 2.  相似文献   

20.
Lead-free piezoelectric ceramics 0.92(Bi0.5Na0.5)TiO3-0.08BaTiO3 + xmol% Co3+ (BNBT-Co, x = 0-8) are prepared by the solid state reaction method. Effects of the amount of Co^3+ on the electrical properties and phase transition are studied. The results indicate that the addition of Co^3+ enhances the mechanical quality factor Q^3+ significantly, whereas the dissipation factor tanδ has a minimum value at x = 3.5. Meanwhile, addition of Co^3+ leads to small decreases of piezoelectric constant d33, and planar electromechanical coupling kp. The present 0.92(Bio.aNao.5) TiO3-0.08BaTiO3+3.5 moi% Co^3+ ceramics exhibit good performance with mechanical quality factor Qm = 910, piezoelectric constant d33 = 106pC/N, planar electromechanical coupling kp =10% and dissipation factor tanδ = 1.1% at 1 kHz. Saturated polarization hysteresis loops have been obtained for BNBT-Co ceramics. Two dielectric peaks at depolarization temperature Td and Tm appear in the curves of ε33^T vs temperature for the pure BNBT ceramics. However, the first dielectric peak Td disappears after the addition of Co^3+, which means that the transition from ferroelectric to antiferroelectric phase has been eliminated.  相似文献   

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