Xiangyong Zhao

A high-performance flexible piezoelectric energy harvester based on lead-free (Na0.5Bi0.5)TiO3–BaTiO3 piezoelectric nanofibers

Recently wearable energy harvesters have attracted great attention due to their vital importance in portable energy-harvesting and personal electronics. Here we report a high-performance flexible piezoelectric energy harvester based on superior environmentally friendly 0.93(Na0.5Bi0.5)TiO3–0.07BaTiO3 (NBT–0.07BT) nanofibers. High-quality lead-free NBT–0.07BT fibers were synthesized by a sol–gel based electrospinning method. X-ray diffraction (XRD), scanning electron microscopy (SEM), piezoresponse force microscopy (PFM), and high-resolution transmission electron microscopy (HRTEM) were utilized to characterize the morphologies, phase structures, domain structures, and local piezoelectric response. The NBT–0.07BT nanofibers, which were located at the morphotropic phase boundary (MPB), exhibited a pure perovskite structure and superior local piezoelectric response (the effective normalized strain constant d33,eff reached up to ∼109 pm V−1 for single NBT–0.07BT nanofibers). The flexible piezoelectric energy harvester based on the NBT–0.07BT nanofibers exhibited a high peak voltage output of ∼30 V under 1 MΩ load resistance when applying a dynamic load using a finger and the short-circuit peak current reached ∼80 nA. Upon periodic mechanical impact, electrical energy was repeatedly generated from the device to power a commercial light-emitting diode. The advantages of small size, ease of processing, high flexibility, and environmental friendliness make this lead-free piezoelectric device quite promising for application in portable electronics.

Giant electrostrain accompanying structural evolution in lead-free NBT-based piezoceramics

High-performance (Na0.5Bi0.5)TiO3 (NBT) lead-free incipient ceramics are promising piezoactuator materials, but high driving fields to deliver the large strain limits their practical applications. Herein, we report a giant piezoelectric strain (d33*) of 810 pm V−1 at a low driving field of 4 kV mm−1 in a novel ternary (0.94 − x)(Na0.5Bi0.5)TiO3–0.06Ba(Zr0.05Ti0.95)O3−x(Sr0.8Bi0.1□0.1)TiO2.95 solid solution with x = 0.05 (SBT5). The field of SBT5 critical composition is notably reduced compared with other NBT-based ceramics, while its strain properties are maintained at a high level along with an excellent thermal stability. The dopant induces a randomly distributed local polarization field, which breaks the symmetry of Landau potential curves, boosts the ferroelectric instability and favors a more disordered relaxor structure. The giant strain in the critical composition SBT5 is due to a field-induced reversible relaxor-ferroelectric phase transformation, while the reduced driving field results from two synergistic effects: remanent quasi-ferroelectric order as the seed for the growth of polar domains helps the system skip the nucleation process; the local defects further facilitate the growth of ferroelectric domains. The composition, temperature and electric-field dependence of structural evolutions were systematically elucidated from the micro- and macroscopic view. This study opens up a feasible and effective way for achieving giant electrostrain in lead-free actuator materials.

Effects on structure and properties of BCZT lead-free piezoelectric ceramics by rare-earth doping

ABSTRACT 1 mol% rare-earth element doped [(Ba0.85Ca0.15)0.99Re0.01](Zr0.1Ti0.9)O3 (BCZT-Re, Re = La, Sm, Yb, Eu and Er) lead-free piezoelectric ceramics were prepared by the conventional ceramic processing using high-purity carbonates and oxides as raw materials. The BCZT-Re ceramics sintered at 1450°C exhibit pure rhombohedral perovskite structure approaching the morphotropic phase boundary (MPB) composition accompanied by different relative density and grain size distribution. The dielectric behavior of the BCZT-Re ceramics approaches normal ferroelectrics but with slightly broad dielectric response peaks, and can be fitted well by the Curie-Weiss law above the Curie temperature TC but in a limited temperature range. Besides the La doping, the other BCZT-Re ceramics present symmetric and saturated P-E hysteresis loops, in which the BCZT-Eu ceramics exhibit apparently large values of polarization remnant Pr and coercive field Ec. The Pr and Ec values decrease rapidly around 80–90°C, depending on compositions, in the BCZT-Re ceramics, determining their safe use temperatures. Excellent fluorescence performance with different photoluminescence emission intensity and light color is induced by the rare-earth doping in the BCZT-Re ceramics, which can meet the requirements of the multifunctional applications using the ferroelectric-based materials.

Effects of nano-sized BCZT on structure and electrical properties of KNN-based lead-free piezoceramics

The (1 − x)(Li0.03Na0.5K0.47)(Nb0.92Sb0.05Ta0.03)O3–xBa0.85Ca0.15Zr0.1Ti0.9O3 (LNKNST–BCZT, x = 0, 0.5, 1.5, 2.5, and 3.5%) lead-free piezoceramics were synthesized by the conventional solid-state reaction method with adding nano-sized Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) powder to investigate their influences on crystal structure and electrical properties. The X-ray diffraction (XRD) analysis reveals that all the sintered LNKNST–BCZT ceramics exhibit pure perovskite structure with the mainly rhombohedral (R) phase or the coexistence of rhombohedral (R) phase and tetragonal (T) phase. The composition of the LNKNST–1.5%BCZT ceramics locates around the critical point, i.e., the ceramics changing from the coexistence of rhombohedral (R) phase and tetragonal (T) phase to purely rhombohedral (R) phase, and presents the most densified microstructure morphology, which can be confirmed further by the field emission scanning electron microscope (FESEM) observation. There are two dielectric anomalies in the temperature dependent dielectric properties curves of the LNKNST–BCZT ceramics, which correlate with the ferroelectric rhombohedral (R) phase changing to the ferroelectric tetragonal (T) phase, and then to the paraelectric cubic (C) phase. Both the Curie–Weiss law and the power law fittings confirm the diffuse phase transition ferroelectrics characteristic of the LNKNST–1.5%BCZT ceramics, which is considered as correlating with the polar nanoregions (PNRs). Due to the densification effect caused by the chosen amount of nano-sized BCZT doping and the construction of R–T polymorphic phase boundary, the LNKNST–1.5%BCZT ceramics exhibit the best ferroelectric and piezoelectric properties. The complex impedance spectroscopy analysis confirms that the extrinsic electrical conduction mechanism at high temperatures is dominated by the oxygen vacancies induced by the evaporation of the alkali metals during sintering.

In situ reversible tuning of photoluminescence of an epitaxial thin film via piezoelectric strain induced by a Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystal

Conventionally, photoluminescence (PL) properties are mainly modulated through traditional chemical approaches which are ex situ, irreversible and static modulation techniques, potentially limiting the understanding of the detailed process of luminescence and smart PL applications. Here, an in situ dynamic routine is developed to tune the PL response in an epitaxial Yb3+/Er3+ co-doped BaTiO3 thin film through electric-field-induced strain of a piezoelectric single-crystal Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) substrate. A reversible tuning and enhancement of the PL intensity was achieved when an external electric field was applied to the PMN–PT single-crystal substrate. The underlying mechanism responsible for the dynamic enhancement of the PL intensity was attributed to the strain induced lower host symmetry so as to enhance the hypersensitive transition probability of the rare-earth ions. The present work could provide a significant guide for the in situ dynamic and active modulation of the PL performances of luminescent devices through the piezoelectric strain.

Domain configuration evolution, dielectric, ferroelectric and piezoelectric properties of 0.32PIN–0.345PMN–0.335PT single crystals

Domain configuration evolution with temperature of the unpoled [001]C-oriented 0.32Pb(In1/2Nb1/2)O3–0.345Pb(Mg1/3Nb2/3)O3–0.335PbTiO3 (0.32PIN–0.345PMN–0.335PT) single crystals was studied by the polarized light microscopy (PLM). The optical observation of the domain structures reveals the coexistence of polymorphic ferroelectric phases with mainly ferroelectric monoclinic phase at room temperature and the irreversible domain evolution upon thermal cycling, which induce the high piezoelectric response in such relaxor-based ferroelectric single crystals with the morphotropic phase boundary compositions combined with polarization rotation. The temperature dependent domain evolution and dielectric behavior demonstrate the successive temperature-induced second-order ferroelectric M phase to ferroelectric tetragonal (T) phase (FEM–FET) and first-order ferroelectric T phase to paraelectric cubic (C) phase (FET–PC) ferroelectric phase transitions in the unpoled 0.32PIN–0.345PMN–0.335PT single crystals. Two dielectric loss anomalies were detected around the dielectric anomaly below 100 °C in the poled 0.32PIN–0.345PMN–0.335PT single crystals, indicating that the FEM–FET phase transition can be correlated with two different ferroelectric phase transitions, one is MA–MC, and the other is MC–T phase transition. The FEM–FET phase transition was confirmed further by the energy density measurement. The temperature dependent piezoelectric properties proved that the working temperature of the 0.32PIN–0.345PMN–0.335PT single crystals can reach 130 °C, higher around 50 °C than the Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals, indicating their promising applications in transducers used at elevated temperatures.

High frequency transducer for vessel imaging based on lead-free Mn-doped (K0.44Na0.56)NbO3 single crystal

We report a high frequency ultrasonic transducer up to 50 MHz for vessel imaging based on a lead-free (K0.44Na0.56)NbO3–0.5 mol. % Mn (Mn-KNN) single crystal, which has a high electromechanical coupling coefficient kt of 0.64 and a large thickness frequency constant Nt of 3210 kHz · mm. The Krimholtz, Leedom, and Mattaei (KLM) equivalent circuit model was utilized to simulate and optimize the pulse-echo response combined with PiezoCAD software. Theoretically, a high -6 dB bandwidth of 74.94% was obtained at a center frequency of 50.47 MHz and optimized matching conditions. The experimental results showed a center frequency of 51.8 MHz with a −6 dB bandwidth of 70.2%. The excellent global performance makes this lead-free single-crystal transducer quite potential in an environmentally friendly vessel imaging transducer.

Enhanced pyroelectric properties and thermal stability of Mn-doped 0.29Pb(In1/2Nb1/2)O3-0.29Pb(Mg1/3Nb2/3)O3–0.42PbTiO3 single crystals

The pyroelectric properties and thermal stability of a [001]-oriented tetragonal 1 mol. % Mn-doped 0.29Pb(In1/2Nb1/2)O3-0.29Pb(Mg1/3Nb2/3)O3-0.42PbTiO3 [Mn-PIN-PMN-PT(29/29/42)] ternary single crystal were investigated. The single crystal exhibited a high pyroelectric coefficient of p = 6.0 × 10−4 C m−2 K−1 and figures of merit (FOMs) at 1 kHz for a current responsivity of Fi = 2.4 × 10−10 mV−1, a voltage responsivity of Fv = 0.08 m2 C−1, and a detectivity of Fd = 19.8 × 10−5 Pa−1/2 which were weakly dependent on frequency. These all increased linearly upon increasing temperature to 120 °C. Furthermore, the values of p for the ternary single crystal were weakly dependent on thermal annealing temperatures (Ta), maintaining over 75% of the original value at Ta < 160 °C, which was 70 °C higher than that of the [111]-oriented rhombohedral 1 mol. % Mn-doped 0.73Pb(Mg1/3Nb2/3)O3–0.27PbTiO3 [Mn-PMN-PT(73/27)] binary single crystal. These excellent pyroelectric properties, together with good thermal stability and wide operational temperature, make the [001]-oriented tetragonal Mn-PIN-PMN-PT(29/29/42) single crystal a promising candidate for pyroelectric detection and thermal imaging applications.The pyroelectric properties and thermal stability of a [001]-oriented tetragonal 1 mol. % Mn-doped 0.29Pb(In1/2Nb1/2)O3-0.29Pb(Mg1/3Nb2/3)O3-0.42PbTiO3 [Mn-PIN-PMN-PT(29/29/42)] ternary single crystal were investigated. The single crystal exhibited a high pyroelectric coefficient of p = 6.0 × 10−4 C m−2 K−1 and figures of merit (FOMs) at 1 kHz for a current responsivity of Fi = 2.4 × 10−10 mV−1, a voltage responsivity of Fv = 0.08 m2 C−1, and a detectivity of Fd = 19.8 × 10−5 Pa−1/2 which were weakly dependent on frequency. These all increased linearly upon increasing temperature to 120 °C. Furthermore, the values of p for the ternary single crystal were weakly dependent on thermal annealing temperatures (Ta), maintaining over 75% of the original value at Ta < 160 °C, which was 70 °C higher than that of the [111]-oriented rhombohedral 1 mol. % Mn-doped 0.73Pb(Mg1/3Nb2/3)O3–0.27PbTiO3 [Mn-PMN-PT(73/27)] binary single crystal. These excellent pyroelectric properties, together with good thermal stability and...

Improving densification and electrical properties of KNN-based lead-free piezoceramics via two-step sintering method

ABSTRACT The 0.95(Li0.03Na0.5K0.47)(Nb0.92Sb0.05Ta0.03)O3-0.05(Ba0.5Ca0.5)ZrO3 (LNKNST-BCZ) lead-free piezoelectric ceramics were prepared by the conventional ceramic processing via the two-step sintering method. The phase structure purity and electrical properties of the LNKNST-BCZ ceramics can be improved further by tailoring the sintering temperature and sintering time. Rather pure perovskite structure with the coexistence of ferroelectric rhombohedral (R) and tetragonal (T) phases can be obtained in the LNKNST-BCZ ceramics via the two-step sintering method confirmed by the X-ray diffraction (XRD) analysis. Sintered at optimized conditions the LNKNST-BCZ ceramics present high densification and rather homogeneous microstructure morphology. The Curie-Weiss law and the quadratic law fitting prove that the dielectric behavior of the LNKNST-BCZ ceramics approaches closer to the normal ferroelectrics with slight diffused phase transition characteristic. The LNKNST-BCZ ceramics sintered at 1180°C for 0.5 h exhibit the optimum dielectric, ferroelectric and piezoelectric properties. The improvement of the densification and piezoelectric properties of the LNKNST-BCZ ceramics can be attributed to the polymorphic R-T phase boundary and densified microstructure morphology induced by (Ba0.5Ca0.5)ZrO3 (BCZ) doping and two-step sintering method.

Nanoscale insight of high piezoelectricity in high-TC PMN-PH-PT ceramics

The piezoelectric properties of the high-Curie temperature (high-TC) 0.15Pb(Mg1/3Nb2/3)O3-0.38PbHfO3-0.47PbTiO3 (0.15PMN-0.38PH-0.47PT) ceramics prepared by three different methods were compared. The 0.15PMN-0.38PH-0.47PT ceramics synthesized by the partial oxalate route exhibit the optimum properties, in which d33* = 845.3 pm/V, d33 = 456.2 pC/N, Kp = 67.2%, and TC = 291 °C. The nanoscale origin of the high piezoelectric response of the 0.15PMN-0.38PH-0.47PT ceramics was investigated by piezoresponse force microscopy (PFM) using the ceramics synthesized by the partial oxalate route. Large quantities of fine stripe submicron ferroelectric domains are observed, which form large island domains. In order to give further insights into the piezoelectric properties of the 0.15PMN-0.38PH-0.47PT ceramics from a microscopic point of view, the local poling experiments and local switching spectroscopy piezoresponse force microscopy (SS-PFM) were investigated, from which the local converse piezoelectric coefficient d33*(l) is calculated as 220 pm/V.The piezoelectric properties of the high-Curie temperature (high-TC) 0.15Pb(Mg1/3Nb2/3)O3-0.38PbHfO3-0.47PbTiO3 (0.15PMN-0.38PH-0.47PT) ceramics prepared by three different methods were compared. The 0.15PMN-0.38PH-0.47PT ceramics synthesized by the partial oxalate route exhibit the optimum properties, in which d33* = 845.3 pm/V, d33 = 456.2 pC/N, Kp = 67.2%, and TC = 291 °C. The nanoscale origin of the high piezoelectric response of the 0.15PMN-0.38PH-0.47PT ceramics was investigated by piezoresponse force microscopy (PFM) using the ceramics synthesized by the partial oxalate route. Large quantities of fine stripe submicron ferroelectric domains are observed, which form large island domains. In order to give further insights into the piezoelectric properties of the 0.15PMN-0.38PH-0.47PT ceramics from a microscopic point of view, the local poling experiments and local switching spectroscopy piezoresponse force microscopy (SS-PFM) were investigated, from which the local converse piezoelectric coefficient d...