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1.
A composition-induced pseudocubic–tetragonal structural transition was found to be accompanied by a relaxor phase transformation in xBi(Mg0.5Ti0.5)O3–(0.75  x)PbTiO3–0.25(Bi0.5Na0.5)TiO3 ternary solid solutions. Dielectric and ferroelectric measurements suggest the coexistence of ergodic and nonergodic relaxor phases within a single pseudocubic phase zone for samples with 0.50 < x < 0.51 where large electromechanical strains of up to 0.43% (Smax/Emax = 621 pm/V) can be generated. The mechanism was mainly ascribed to the accumulated effects of field-modulated continuous and reversible transformations from a pseudocubic ergodic phase to a rhombohedral short-range ordered phase (but not nonergodic polar phase), and finally to a long-range ordered ferroelectric tetragonal phase. These procedures were found to be strongly dependent on the applied field magnitudes. These findings were reasonably approved by a couple of measurements such as dielectric–temperature–frequency spectrum, ferroelectric polarization/strain hysteresis loops, polarization current density curves and particularly ex situ Raman spectrum and in situ high-resolution synchrotron X-ray diffraction.  相似文献   

2.
The microstructure, electric-field-induced strain, polarization, and dielectric permittivity in (Bi0.5Na0.5)0.945−x(Bi0.2Sr0.70.1)xBa0.055TiO3 (BNBT–xBST) (0  x  0.08) electroceramics are investigated. An irreversible transition from rhombohedral and monoclinic coexistence phase to single rhombohedral phase is indicated with the remnant strain Sr = 0.330% at x = 0. As the BST content increases, the ferroelectric order is disrupted resulting in a degradation of the remnant polarization, coercive field, and the ferroelectric-to-relaxor transition temperature (TF–R). The coexistence of ferroelectric relaxor and ferroelectric phase is observed for the optimum composition x = 0.02 at ambient temperature with a large strain of 0.428% at 60 kV/cm (normalized strain Smax/Emax = 713 pm/V). The large strain is contributed by both ferroelectric domain reorientation behavior and the reversible relaxor to ferroelectric phase transition.  相似文献   

3.
Ternary solid solutions of (1 ? x)(0.8Bi0.5Na0.5TiO3–0.2Bi0.5K0.5TiO3)– xNaNbO3 (BNKT–xNN) lead‐free piezoceramics were fabricated using a conventional solid‐state reaction method. Pure BNKT composition exhibited an electric‐field‐induced irreversible structural transition from pseudocubic to ferroelectric rhombohedral phase at room temperature. Accompanied with the ferroelectric‐to‐relaxor temperature TF‐R shifted down below room temperature as the substitution of NN, a compositionally induced nonergodic‐to‐ergodic relaxor transition was presented, which featured the pinched‐shape polarization and sprout‐shape strain hysteresis loops. A strain value of ~0.445% (under a driving field of 55 kV/cm) with large normalized strain of ~810 pm/V was obtained for the composition of BNKT–0.04NN, and the large strain was attributed to the reversible electric‐field‐induced transition between ergodic relaxor and ferroelectric phase.  相似文献   

4.
《Ceramics International》2017,43(16):13612-13617
0.8Bi0.5Na0.5Ti(1-x)NbxO3−0.2Sr0.85Bi0.1TiO3 (BNT-SBT-xNb, x = 0.00, 0.01, 0.02, and 0.03) piezoelectric ceramics were prepared by traditional solid state reaction and the influence of Nb substitution on the phase structure, ferroelectric, piezoelectric, and electric-field-induced strain properties in BNT-SBT ceramics were studied. XRD results exhibited that Nb5+ ions could fully diffuse into BNT-SBT structure to form a solid solution when x = 0.01. P-E loops and S-E curves suggested that the ferroelectric phase transformed to ergodic relaxor state (FE-to-ER) with the increasing the amount of Nb additive, indicating the ferroelectric long-ranged order was disturbed by the excess of Nb. With increasing Nb doping, phase transition temperature from normal ferroelectric to ergodic relaxor (short for TF-R) could be reduced from 120 °C to 40 °C. Furthermore, for sample with x = 0.01, the normalized strain d33* got a maximum value ~571 pm/V due to the phase transition from ergodic relaxor to ferroelectric (ER-to-FE) under electric field.  相似文献   

5.
《Ceramics International》2016,42(8):9419-9425
Lead-free piezoelectric ceramics (Bi0.5Na0.5)0.935Ba0.065Ti1−x(Fe0.5Sb0.5)xO3 (BNBT6.5–xFS, x=0.005, 0.010, 0.015, 0.020) were prepared by a conventional solid sintering technique. The effects of B-site doping of (Fe, Sb) on the phase structure, microstructure, dielectric, ferroelectric, and piezoelectric properties of BNBT6.5 ceramics were systematically investigated. Results showed that (Fe, Sb) can completely diffuse in the BNBT6.5 lattice in the all studied components. The addition of (Fe, Sb) destroyed the ferroelectric long-range order, and thus promoted the electric field induced strain response. The maximum electric field-induced strain (Smax=0.37%) with normalized strain (d33*=Smax/Emax=454 pm/V) at an applied electric field of 80 kV/cm was obtained at x=0.015. Temperature dependent measurements of both polarization and strain from room temperature to 120 °C suggested that the origin of the large strain is due to a reversible field-induced ergodic relaxor to ferroelectric phase transformation.  相似文献   

6.
《Ceramics International》2016,42(8):9660-9666
Lead-free 0.99[(1−x)(Bi0.5Na0.5)TiO3-x(Bi0.5K0.5)TiO3]–0.01Ta piezoelectric ceramics were prepared by a conventional solid-state reaction process. The ferroelectric properties, and strain behaviors were characterized. Increase of the (Bi0.5K0.5)TiO3 content induces a phase transition from coexistence of ferroelectric tetragonal and rhombohedral to a relaxor pseudocubic phase. Accordingly, the ferroelectric order is disrupted significantly with the increase of (Bi0.5K0.5)TiO3 content and the destabilization of the ferroelectric order is accompanied by an enhancement of the unipolar strain, which peaks at a value of 0.35% (corresponding to a large signal d33 of 438 pm/V) in samples with 20 mol% (Bi0.5K0.5)TiO3 content. Temperature dependent measurements of both polarization and strain from room temperature to 120 °C suggested that the origin of the large strain is due to a reversible field-induced nonpolar pseudocubic-to-polar ferroelectric phase transformation.  相似文献   

7.
《Ceramics International》2016,42(12):13783-13789
Lead-free (1−x)(0.0852Bi0.5Na0.5TiO3–0.12Bi0.5K0.5TiO3–0.028BaTiO3)–xCaZrO3 piezoelectric ceramics (BNT−BKT−BT−xCZ, x=0, 0.01, 0.02, 0.03, 0.04 and 0.05) were prepared by using a conventional solid-state reaction method. The effects of CZ-doping on the structural, dielectric, ferroelectric and piezoelectric properties of the BNT−BKT−BT−xCZ system were systematically investigated. The polarization and strain behaviors indicated that the long-range ferroelectric order in the unmodified BNT−BKT−BT ceramics was disrupted by the increase of CZ-doping content, and correspondingly the depolarization temperature (Td) shifted down from 109 °C to below room temperature. When x>0.03, accompanied with the drastic decrease in the remnant polarization (Pr) and piezoelectric coefficient (d33), the electric-field-induced strain was enhanced significantly. A large unipolar strain of 0.35% under an applied electric field of 70 kV/cm (Smax/Emax=500 pm/V) was obtained in the BNT−BKT−BT−0.04CZ ceramics at room temperature, which was attributed to the reversible electric-field-induced phase transition between the relaxor and ferroelectric phases.  相似文献   

8.
The electric field-induced strain of Bi1/2(Na0.82K0.18)1/2TiO3 (BNKT) ceramics modified with BaZrO3 (BZ) was investigated as a function of composition and temperature. Unmodified BNKT ceramics revealed a typical ferroelectric butterfly-shaped bipolar S–E loop at room temperature, whose normalized strain (Smax/Emax) showed a significant temperature coefficient of 0.38 pm/V/K. As the BZ content increased in the solid solution up to 5 mol%, the ferroelectric BNKT gradually transformed to a relaxor. Finally, 5 mol% BZ-modified BNKT ceramics showed a typical electrostrictive behavior with a thermally stable electrostrictive coefficient (Q33) of 0.025 m4/C2, which is comparable to that of Pb(Mg1/3Nb2/3)O3 (PMN) ceramics that have been primarily used as Pb-based electrostrictive materials.  相似文献   

9.
《Ceramics International》2016,42(13):14886-14893
Lead–free piezoelectric ceramics (Bi0.5Na0.5)0.935Ba0.065Ti1–x(Mn0.5Sb0.5)xO3 (BNBT6.5–xMS, x=0.005, 0.010, 0.015, 0.020) were prepared by conventional solid state reaction sintering technique. All ceramics present a pure perovskite phase structure, indicating that (Mn, Sb) has completely diffused into the BNBT6.5 lattice in the studied components. The addition of (Mn, Sb) disrupted the ferroelectric long–range order and promoted the electric field induced strain response. At x=0.015, a large electric field–induced unipolar strain of 0.48% (at an applied electric field of 80 kV/cm) with normalized strain d33*(Smax/Emax) of 602 pm/V are achieved. Temperature dependent measurements of both polarization and strain from room temperature to 120 °C were also studied, and the results suggest that the origin of the large strain is due to a reversible field–induced non–polar relaxor phase to polar ferroelectric phase transformation.  相似文献   

10.
Lead‐free 0.985[(0.94?x)Bi0.5Na0.5TiO3–0.06BaTiO3xSrTiO3]–0.015LiNbO3 [(BNT–BT–xST)–LN, x=0‐0.05] piezoelectric ceramics were prepared using a conventional solid‐state reaction method. It was found that the long‐range ferroelectric order in the unmodified (BNT–BT)–LN ceramic was disrupted and transformed into the ergodic relaxor phase with the ST substitution, which was well demonstrated by the dramatic decrease in remnant polarization (Pr), coercive field (Ec), negative strain (Sneg) and piezoelectric coefficient (d33). However, the degradation of the ferroelectric and piezoelectric properties was accompanied by a significant increase in the usable strain response. The critical composition (BNT–BT–0.03ST)–LN exhibited a maximum unipolar strain of ~0.44% and corresponding normalized strain, Smax/Emax of ~880 pm/V under a moderate field of 50 kV/cm at room temperature. This giant strain was associated with the coexistence of the ferroelectric and ergodic relaxor phases, which should be mainly attributed to the reversible electric‐field‐induced transition between the ergodic relaxor and ferroelectric phases. Furthermore, the large field‐induced strain showed relatively good temperature stability; the Smax/Emax was as high as ~490 pm/V even at 120°C. These findings indicated that the (BNT–BT–xST)–LN system would be a suitable environmental‐friendly candidate for actuator applications.  相似文献   

11.
In this study, the Bi-nonstoichiometric 0.99Bix(Na0.8K0.2)0.5TiO3-0.01SrTiO3 (BNKST) ceramics with x = 0.5–0.535 mol (Bi50-Bi53.5) were prepared by a conventional solid-state reaction method. The effects of Bi excess on structural transition and ferroelectric stability of BNKST ceramics were systematically investigated by the Raman spectra, dielectric analyses and electromechanical measurements. The introduction of excess Bi3+ could significantly break the long-range ferroelectric order and favor the presence of relaxor phase, then the ferroelectric-relaxor transition temperature (TFR) can be effectively tuned to around room temperature by Bi nonstoichiometry, giving rise to an enhanced room-temperature strain property. The positive strain Spos and dynamic piezoelectric constant d33* of Bi52.5 critical composition reach 0.33% and 440 pm/V, respectively at 6 kV/mm. The high recoverable strain of Bi52.5 sample can be attributed to the electric-field-induced reversible relaxor-ferroelectric phase transition. The present work may be helpful for further understanding and designing high-performance NBT-based lead-free ceramics for piezoelectric actuator applications.  相似文献   

12.
Lead-free piezoelectric (1 ? x)Bi0.5(Na0.78K0.22)0.5TiO3xK0.5Na0.5NbO3 (BNKT–xKNN, x = 0–0.10) ceramics were synthesized using a conventional, solid-state reaction method. The effect of KNN addition on BNKT ceramics was investigated through X-ray diffraction (XRD), dielectric, ferroelectric and electric field-induced strain characterizations. XRD revealed a pure perovskite phase with tetragonal symmetry in the studied composition range. As the KNN content increased, the depolarization temperature (Td) as well as maximum dielectric constant (?m) decreased. The addition of KNN destabilized the ferroelectric order of BNKT ceramics exhibiting a pinched-type hysteresis loop with low remnant polarization (11 μC/cm2) and small piezoelectric constant (27 pC/N) at 3 mol% KNN. As a result, at x = 0.03 a significant enhancement of 0.22% was observed in the electric field-induced strain, which corresponds to a normalized strain (Smax/Emax) of ~434 pm/V. This enhancement is attributed to the coexistence of ferroelectric and non-polar phases at room temperature.  相似文献   

13.
Bi0.5Na0.5TiO3-based lead-free piezoceramics with large strain output are of great importance in the application of piezoelectric actuators. AgNbO3-modified 0.76Bi0.5Na0.5TiO3-0.24SrTiO3 (BNT-24ST) lead-free piezoceramics were synthesized by conventional solid-state reaction method. The effects of AgNbO3 on the structures, dielectric, ferroelectric and piezoelectric properties were carefully investigated. A large electrostrain and normalized strain (d33* = Smax/Emax) of 0.27% and 700?pm/V, were obtained respectively at low electric field (40?kV/cm) for 1?mol.% AgNbO3-doped BNT-24ST. AgNbO3 doping modified the phase composition which contained moderate amounts of tetragonal and rhombohedral phase by shifting its TF-R to below room temperature. Moreover, the reversible field-induced phase transition between relaxor and ferroelectric made contributions to its large strain related properties. This work has confirmed that the actuating performance of BNT-ST-based piezoceramics can be further improved by an easy and cost-effective composition engineering method and showed it a promising candidate for lead-free actuator material.  相似文献   

14.
Lead-free piezoceramics with the composition 0.7(Bi1-xNdx)FeO3-0.3BaTiO3+0.1 wt% MnO2 (BNxF-BT) were prepared using a conventional solid state route. X-ray diffraction and temperature dependent permittivity measurements indicated a transition from a composition lying at a morphotropic phase boundary (MPB) to a pseudocubic phase as a function of Nd concentration. The highest maximum strain (Smax  0.2% at 60 kV/cm) and effective piezoelectric coefficient (d33* = 333 pm/V) were obtained at room temperature for the composition BN0.02F-BT. The decrease in remanent polarization (Pr) and Berlincourt d33 with increase in Nd concentration can be attributed to the coexistence of ferroelectric and relaxor phases. In-situ polarisation and strain measurements revealed an increase in Pr and d33* with temperature and a reduction in the coercive field EC. Presumably this behavior is due to a combination of thermally activated domain wall motion and lowering of the activation energy for a field induced relaxor-ferroelectric transition, as the Curie maximum is approached.  相似文献   

15.
《Ceramics International》2017,43(10):7516-7521
The crystal structure, ferroelectric, and electric-field-induced strain (EFIS) properties of Bi-based lead-free ferroelectric/relaxor composite materials are investigated. Bi1/2(Na0.82K0.18)1/2TiO3 as a ferroelectric material and 0.98Bi1/2(Na0.78K0.22)1/2TiO3‒0.02LaFeO3 as a relaxor were synthesized via conventional ceramic processing routes while the relaxor (matrix phase) was prepared via high-energy ball milling (HEBM) after calcination. The average particle size was decreased via HEBM treatment. As a result, a high d33* value of over 600 pm/V was obtained at 4 kV/mm for 30-min HEBM-treated composites. This demonstrates that HEBM treatment is effective in enhancing the strain properties of lead‒free piezoelectric composite materials.  相似文献   

16.
Effect of excess CuO additive on the sintering behavior and piezoelectric properties of Bi0.5(Na82K0.18)0.5TiO3 ceramics was investigated. The addition of small amount of excess CuO as low as 1 mol% was quite effective to lower the sintering temperature (Ts) of BNKT ceramics down to 975 °C while their piezoelectric properties were degraded by Cu doping. However, the electric field-induced strain was markedly enhanced by further addition of Nb2O5 with CuO without elevating Ts. The normalized strain Smax/Emax of 427 pm/V was obtained with a specimen sintered with 0.02 mol CuO and 0.03 mol Nb2O5 in excess.  相似文献   

17.
The (0.94–x)Bi0.5Na0.5TiO3–0.06BaTiO3–x(Sr0.7Bi0.20.1)TiO3 (BNT–BT–xSBT, 0  x  0.24) solid solution ceramics were synthesized via a conventional solid–state reaction method and the correlation of phase structure, piezoelectric, ferroelectric properties and electrocaloric effect (ECE) was investigated in detail. The ECE in lead–free BNT–BT–xSBT ceramics was measured directly using a home–made adiabatic calorimeter with maximum adiabatic temperature change ΔT = 0.4 K with x = 0.08 under the electric field E = 6 kV/mm at room temperature. The position of maximum ECE was found in the vicinity of nonergodic and ergodic phase boundary, where the maximum change in entropy occurs as a result of the field–induced phase transformation between the ergodic and long–range ferroelectric phase. Besides, the mechanism for the shift of ECE peak is discussed in detail. Finally, the temperature dependence of ECE for BNT–BT–xSBT (x = 0, 0.04 and 0.08) was also investigated. This work may present a guideline for designing BNT–based ferroelectric relaxor ceramics for EC cooling technologies.  相似文献   

18.
《Ceramics International》2016,42(3):3938-3946
xCeO2-doped Bi0.487Na0.427K0.06Ba0.026TiO3 lead-free piezoelectric ceramics (BNTC1000x, x=0, 0.3, 0.6, 0.8, 1.0, 1.2, 1.4 wt%), were synthesized by the solid-state reaction method. XRD patterns showed that all BNTC1000x ceramics exhibit pure single perovskite phase. At the critical composition BNTC12, a large electric-field-induced strain of 0.39% with normalized strain (Smax/Emax) of 561 pm/V was obtained under an electric field of 65 kV/cm. The ferroelectric phase was fully poled with electric field, and depoled once the applied electric field was removed. During that cycle, the non-180°-domains repeated switching and back-switching and the large strain was induced. The relaxation behavior was involved in BNTC1000x ceramics and induced by oxygen vacancy migration. Besides, this behavior was more predominant in BNTC12 than in BNTC0.  相似文献   

19.
《Ceramics International》2016,42(12):13960-13968
We investigated the temperature- and frequency-dependent polarization and strain of two bismuth-based perovskite materials, a matrix material and a seed material, with which we formed a composite whose properties we likewise investigated. The chosen matrix material is 0.74Bi0.5Na0.5TiO3–0.26SrTiO3 (BNT-ST) which has a transition point of ~65 °C, from the relaxor to the ferroelectric phase (TR-F). The seed material was Bi0.5(Na0.8K0.2)0.5TiO3 (BNKT), which possesses a TR-F of 120 °C. Different polarization and strain behaviors were observed in the BNT-ST/BNKT composite at different test temperatures. At T=25 °C (<TR-F of the relaxor BNT-ST), the composite exhibited a hysteretic polarization loop and parabolic strain curves which involve an ergodic relaxor-to-normal ferroelectric phase transition with application of an external electric field and the reverse ferroelectric-to relaxor phase transition with removal of the field. When T=80 and 100 °C (>TR-F °f the relaxor BNT-ST and <TR-F of the ferroelectric BNKT), the BNT-ST/BNKT has a slim polarization loop and strain magnitudes that are slightly increased from those of pure BNT-ST. When T=120 °C (~TR-F of the ferroelectric BNKT), the composite has a very slim polarization loop and strain behavior with values that are almost same as those of pure BNT-ST. In addition, the P-S relation for the BNT-ST/BNKT is identical to that of BNT-ST as the operating frequency increases up to 100 Hz. This may be because the polarization of BNT-ST is lower than that of BNKT. The electric field-induced polarization and strain of the BNT-ST/BNKT composite with respect to the temperature and frequency are related to the thermal stability of the ferroelectric seed and the degree of the phase transition in the relaxor matrix.  相似文献   

20.
Lead-free Bi0.5Na0.5TiO3-SrTiO3 incipient piezoceramics with Li2CO3 and MnO2 additives were successfully fabricated at low firing temperature for applications in co-fired multilayer piezoactuators. The addition of Li2CO3 effectively shifted the sintering temperature from 1230 °C down to 1075 °C, where the ceramics were co-fired with a Ag/Pd (75/25) inner electrode. The prototype actuators were prepared by tape-casting method using ceramics with the composition of 0.74Bi0.5Na0.5TiO3-0.26 SrTiO3 + 0.15 wt%MnO2 + 0.45 wt%Li2CO3. The total number of active layers was 13, and each ceramic layer had a thickness of 60 μm. The actuator output a large strain up to ∼0.20% at a driving field of 4 kV/mm, due to the field-induced phase transition between the ergodic relaxor and ferroelectric phases. The excellent voltage-displacement performance of the prototype actuator demonstrates the potential for industrial applications.  相似文献   

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