Large-signal Piezoelectric Coefficient Research Articles

Temperature-insensitive electric-field-induced strain and enhanced piezoelectric properties of textured (K,Na)NbO3-based lead-free piezoceramics

Texturing is an effective method to improve the piezoelectric properties of lead-free piezoceramics. In the present study, textured (K,Na)NbO3-based piezoceramics with a Lotgering factor of 89.7% were successfully fabricated by the templated grain growth (TGG) method. Compared with its non-textured counterparts, great enhancements of the piezoelectric coefficient (50% improvement) and electromechanical coupling factor are observed in the textured samples. More importantly, electric-field-induced strain is also remarkably improved, as evident by a 17% higher large-signal piezoelectric coefficient (346 pm/V) of the textured sample. A relatively low strain deviation of 2% is observed between room temperature and 150 °C, and even up to 175 °C, 86% of their room temperature large-signal piezoelectric coefficient value is maintained. This temperature stability of textured (K,Na)NbO3-based piezoceramics is of great significance for actuators with a stable response over a broad temperature range.

Large strain with low hysteresis in Bi4Ti3O12 modified Bi1/2(Na0.82K0.18)1/2TiO3 lead-free piezoceramics

In order to obtain BNT-based ceramic system with excellent electric-field-induced strain performance for actuator applications, a novel solid solution (100-x)Bi1/2(Na0.82K0.12)1/2TiO3-xBi4Ti3O12 ((100-x)BNKT-xBiT, x = 0–12 wt%) was designed and fabricated by solid state synthesis. The microstructure and related electrical properties of this material were systematically investigated. It was found that BiT is dissolved into the lattice structure of the BNKT, leading to a greater increase in the volatilization of Na and K, thus produce more A-site vacancies compared with the undoped BNKT. The 9 wt%BiT doped sample not only has sufficient A-site vacancies to destroy the long-range ferroelectric order of the base composition but also favors the presence of extremely stable relaxor phase at room temperature. Further, the ferroelectric-to-relaxor phase transition temperature TF-R can be effectively tuned to about 0 °C, giving rise to a large signal piezoelectric coefficient d*33 of 485 pm/V with a small hysteresis η of 23%.

Origin of enhanced piezoelectric properties and room temperature multiferroism in MnO2 added 0.90(Li0.12Na0.88NbO3)-0.10BaTiO3 ceramic

Room temperature multiferroism with enhanced ferro and piezoelectric properties of a new lead-free MnO2 added 0.90(Li0.12Na0.88NbO3)-0.10BaTiO3 ceramic is reported. The addition of MnO2 as an additive resulted in a two fold increase in remnant polarization (Pr) (from ~7.30 to 17.20μC/cm2), ~50% increase in large-signal piezoelectric coefficient (d33∗) (from ~117 to176pm/V) and symmetric butterfly loop are observed. Phase analysis revealed that MnO2 entered the host lattice as Mn2+ and Mn4+-ions and induced room temperature ferromagnetic-like character. Interestingly, an intrinsic coupling between the two ferroic orders is evidenced by the observation of a magneto-electric voltage coefficient (αE) of ~0.94mV/cm.Oe.

Thermal-stability of electric field-induced strain and energy storage density in Nb-doped BNKT-ST piezoceramics

In this work, the relationship between the structural mechanisms and macroscopic electrical properties of the Nb-modified 0.96(Bi0.5Na0.84K0.16TiO3)–0.04SrTiO3 (BNKT–ST) system were elucidated by using temperature dependent and in situ synchrotron X-ray diffraction (XRD) techniques. For the composition x = 0.0175, a large-signal piezoelectric coefficient (Smax/Emax = d33*) of 735 pm V−1 at 6 kV mm−1 was observed at room temperature. Interestingly, at a higher temperature of 110 °C, the sample still showed a large d33* of 570 pm V−1. Furthermore, the temperature-invariant electrostrictive coefficient for this sample was found to be 0.0285 m4 C−2 over the temperature range of 25–170 °C. Moreover, the energy density for x = 0.030 sample was ∼1.0 J cm−3 with an energy storage efficiency of ˃70% in the temperature range of 25–135 °C. These results suggest that the synthesized Nb-modified BNKT–ST system is promising for the design of ceramic actuators as well as capacitor applications.

In-situ temperature stability of a piezoelectric accelerometer based on (Bi, Na, K, Li)TiO3 ceramics

This work investigated the in-situ temperature stability of 0.76(Bi0.5Na0.5)TiO3-0.04(Bi0.5Li0.5)TiO3-0.2(Bi0.5K0.5)TiO3 piezoceramics and a compression-mode accelerometer composed of these materials. The temperature-dependent charge sensitivity of the accelerometer was governed by the small-signal piezoelectric coefficient d33 rather than by the large-signal piezoelectric coefficient d*33 of the (Bi,Na)TiO3-based ceramics. The significant decrease in the charge sensitivity in the vicinity of the depolarization temperature is closely related to the main intrinsic contribution to the piezoelectricity, i.e., the decrease in the crystal anisotropy associated with the temperature-induced polar ferroelectric-nonpolar relaxor phase transition.

Influence of composition on the unipolar electric fatigue of Ba(Zr0.2Ti0.8)O3‐(Ba0.7Ca0.3)TiO3 lead‐free piezoceramics

AbstractThe lead‐free (1−x)Ba(Zr0.2Ti0.8)O3‐x(Ba0.7Ca0.3)TiO3 system is considered as promising candidate for the replacement of lead‐based piezoceramics in actuation applications, during which electric fatigue is a major concern. This issue was addressed in this work, where the unipolar fatigue resistance of three (1−x)Ba(Zr0.2Ti0.8)O3‐x(Ba0.7Ca0.3)TiO3 compositions with different crystallographic structures (rhombohedral, orthorhombic, and tetragonal) was evaluated. Strain asymmetry and development of an internal bias field were observed in all compositions. The decrease in the remanent polarization and the large signal piezoelectric coefficient after 107 unipolar cycles was found to lie between 6%‐12% and 2%‐13%, respectively. The most pronounced fatigue was observed for the orthorhombic composition, which has the largest extrinsic contribution to strain. On the other hand, the best fatigue resistance was observed for the tetragonal composition, which has a predominantly intrinsic strain response. The correlation of fatigue resistance with strain mechanism was corroborated with determination of the Rayleigh parameters and changes in the domain morphology after cycling as confirmed by piezoresponse force microscopy.

Giant strain with low cycling degradation in Ta-doped [Bi1/2(Na0.8K0.2)1/2]TiO3 lead-free ceramics

Non-textured polycrystalline [Bi1/2(Na0.8K0.2)1/2](Ti1−xTax)O3 ceramics are fabricated and their microstructures and electrical properties are characterized. Transmission electron microscopy reveals the coexistence of the rhombohedral R3c and tetragonal P4bm phases in the form of nanometer-sized domains in [Bi1/2(Na0.8K0.2)1/2]TiO3 with low Ta concentration. When the composition is x = 0.015, the electrostrain is found to be highly asymmetric under bipolar fields of ±50 kV/cm. A very large value of 0.62% is observed in this ceramic, corresponding to a large-signal piezoelectric coefficient d33* of 1240 pm/V (1120 pm/V under unipolar loading). These values are greater than most previously reported lead-free polycrystalline ceramics and can even be compared with some lead-free piezoelectric single crystals. Additionally, this ceramic displays low cycling degradation; its electrostrain remains above 0.55% even after undergoing 10 000 cycles of ±50 kV/cm bipolar fields at 2 Hz. Therefore, Ta-doped [Bi1/2(Na0.8K0.2)1/2]TiO3 ceramics show great potential for large displacement devices.

Preparation and enhanced electric-field-induced strain of textured 91BNT–6BT–3KNN lead-free piezoceramics by TGG method

oriented 0.91Bi1/2Na1/2TiO3–0.06BaTiO3–0.03(Na,K)NbO3 (BNT–BT–KNN) lead-free piezoceramics were fabricated by templated grain growth method. A high grain orientation degree (Lotgering factor F is 83 %) was achieved with 5 wt% Bi1/2Na1/2TiO3 (BNT) template content and a maximum strain value of 0.226 % was observed, which was 48.7 % higher than that of randomly oriented samples. However, too much BNT template will result in composition deviation from morphotropic phase boundary of BNT–BT–KNN system and disruption of the non-polar phase at zero electric field. All textured samples with 1–10 wt% template addition showed enhanced strain and large signal piezoelectric coefficient $$d_{33}^{*}$$ without disrupting the non-polar phase at zero electric field. The enhanced electric-field-induced strain of the textured sample was primarily attributed to the facilitated phase-transition, which formed a long-range ferroelectric order along the direction.

Preparation and enhanced electrical properties of grain-oriented (Bi1/2Na1/2)TiO3-based lead-free incipient piezoceramics

(Bi1/2Na1/2)TiO3 (BNT) based lead-free incipient piezoceramics are promising candidates for actuator applications due to their giant electromechanical strains originating from the reversible relaxor-ferroelectric phase transition. To decrease the electric field required for this large strain, the templated grain growth method was employed to prepare 〈100〉 oriented 0.91Bi1/2Na1/2TiO3–0.06BaTiO3–0.03AgNbO3 piezoceramics using plate-like BNT templates. Textured samples provided a high unipolar strain of 0.38% and a corresponding large signal piezoelectric coefficient, d33∗ of 766pm/V at 5kV/mm, which are 78% higher than the values of the randomly oriented ones. The enhanced electric-field-induced strain at relatively lower field was attributed primarily to the facilitated phase-transition to form a long range ferroelectric order along the 〈100〉 direction. It was also found that the textured piezoceramics exhibited significantly reduced frequency dependence in the unipolar strain behavior at room temperature, resulting from the decreased electric field required for the relaxor-ferroelectric phase transition.

Stress-dependent electromechanical properties of doped (Ba1−xCax)(ZryTi1−y)O3

Abstract The effect of 1 at% Fe- and FeNb-doping on the temperature and stress stability of the electromechanical properties of (Ba 1− x Ca x )(Zr y Ti 1− y )O 3 (BCZT) was investigated. For the composition (Ba 0.89 Ca 0.11 )(Zr 0.135 Ti 0.865 )O 3 with rhombohedral symmetry, doping reduces the Curie point and the temperature stability of the large-signal electromechanical properties significantly. The large-signal piezoelectric coefficient d 33 * at room temperature was reduced to 500 pm/V compared to 700 pm/V in the undoped composition at 1 kV/mm. The electrostrain, however, was found to be less sensitive to mechanical prestresses, showing a plateau up to stresses of 80 MPa in both doped compositions. These effects were attributed to a reduction of the domain wall mobility due to a smaller grain size, charged defect dipoles and the proximity of the room-temperature measurements to the reduced ferroelectric-paraelectric phase transition temperature. The study reveals that the exceptionally large strains observed in BCZT rely on the instabilities around the polymorphic phase transition in the system. Aliovalent doping changes this sensitive system and reduces the electrostrain considerably.

Relationship between electromechanical properties and phase diagram in the Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 lead-free piezoceramic

The Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 system was synthesized in a wide compositional range in order to study the relationship between its phase diagram and electromechanical properties. Phase transitions were marked using peaks in temperature-dependent permittivity, providing up to three transitions from the rhombohedral phase to an orthorhombic, tetragonal and finally cubic phase, which meet in a region that is termed the phase convergence region in this work. In situ small and large signal electromechanical properties were studied as a function of temperature with specific emphasis on these transitions. A small signal piezoelectric coefficient, d33, presents maximized values at the transition from the orthorhombic to the tetragonal phase, while a large signal piezoelectric coefficient, d33∗, does so at both rhombohedral to orthorhombic and to tetragonal phase transitions. Maximum polarization Pmax was the only quantity determined that had a clear maximum at the phase convergence region.

Electric-field-induced polarization and strain in 0.94(Bi1/2Na1/2)TiO3–0.06BaTiO3 under uniaxial stress

The strain and polarization hystereses of lead-free 0.94Bi1/2Na1/2TiO3–0.06BaTiO3 during unipolar electric field loading are obtained from room temperature to 150°C under uniaxial compressive stress up to 446MPa. At intermediate temperatures a stress-dependent peak evolves in both the maximum strain and polarization. At 125°C a large strain with a large-signal piezoelectric coefficient d33∗ of 884pmV−1 is observed, which decays upon the application of stress. This behavior is rationalized with a change in the primary strain mechanism from domain switching at low temperatures to a reversible electric field-induced transition from an ergodic relaxor state to a long-range order at high temperatures. Moreover, the energy terms w (the output mechanical work) and eP (the charged electrical energy density) that are related to the deformation and the polarization, respectively, are analyzed and used to define a large-signal efficiency η*=w(w+eP)−1. It is found that η* saturates at ∼150MPa but decreases with increasing temperature and electric field. It is furthermore observed that notable strains are achieved at stress levels even far beyond the quasi-statically determined blocking force. Therefore, it is proposed that the presented testing procedure is suited to assess the dynamic actuatoric performance of a piezoceramic.

Effect of K0.5Na0.5NbO3 on Properties at and off the Morphotropic Phase Boundary in Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3 Ceramics

Lead-free (1-y)(Bi1/2Na1/2TiO3–xBi1/2K1/2TiO3)–yK0.5Na0.5NbO3 [(1-y)(BNT–xBKT)–yKNN] (0.1≤x≤0.6 and 0≤y≤0.05) ceramics were prepared with compositions both at as well as off the morphotropic phase boundary (MPB) of x=0.2 and y=0. It was found that KNN addition destabilizes a ferroelectric order in BNT–BKT at zero electric-field, resulting in low remanent polarization, remanent strain and effective small signal d33eff [23 pC/N for (x,y)=(0.2,0.05), 60 pC/N for (0.2, 0.02)], while it does not affect the maximum polarisation and strain at high fields and thus enhances large signal piezoelectric coefficient, d33* [200 pm/V for (0.2,0.05), 217 pm/V for (0.2,0.02)]. This effect of KNN was found to be independent from the MPB and thus equally high d33* values were obtained for compositions at and far off the MPB. Thus, adding KNN to BNT–BKT removes the restriction to remain at exactly MPB position and provides more flexibility while offering equal or even improved strain.

Effect of K0.5Na0.5NbO3on Properties at and off the Morphotropic Phase Boundary in Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3Ceramics

Lead-free (1-y)(Bi1/2Na1/2TiO3–xBi1/2K1/2TiO3)–yK0.5Na0.5NbO3 [(1-y)(BNT–xBKT)–yKNN] (0.1≤x≤0.6 and 0≤y≤0.05) ceramics were prepared with compositions both at as well as off the morphotropic phase boundary (MPB) of x=0.2 and y=0. It was found that KNN addition destabilizes a ferroelectric order in BNT–BKT at zero electric-field, resulting in low remanent polarization, remanent strain and effective small signal d33eff [23 pC/N for (x,y)=(0.2,0.05), 60 pC/N for (0.2, 0.02)], while it does not affect the maximum polarisation and strain at high fields and thus enhances large signal piezoelectric coefficient, d33* [200 pm/V for (0.2,0.05), 217 pm/V for (0.2,0.02)]. This effect of KNN was found to be independent from the MPB and thus equally high d33* values were obtained for compositions at and far off the MPB. Thus, adding KNN to BNT–BKT removes the restriction to remain at exactly MPB position and provides more flexibility while offering equal or even improved strain.