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The high-Curie temperature (TC) 0.15Pb(Mg1/3Nb2/3)O3-0.38PbHfO3-0.47PbTiO3 (PMN-PH-PT) piezoelectric ceramics were prepared by the partial oxalate route via the B-site oxide mixing method. The obtained uniform nm-sized PMN-PH-PT precursor powders provide high calcining and sintering activity for synthesizing ceramics, based on which the synthesis conditions were tailored as calcining at 775 °C and sintering at 1245 °C. The partial oxalate route synthesized PMN-PH-PT ceramics are far superior to the counterparts synthesized by the columbite precursor method and exhibit excellent thermal stability of the piezoelectric properties under TC (∼292 °C), ensuring the potential application in transducers under elevated environmental temperatures. The temperature dependent Raman spectroscopy not only proves the occurrence of the ferroelectric to paraelectric phase transition around TC, but also confirms the successive phase symmetry transitions, which correlate with the polar nanoregions (PNRs) and/or the coexistence of multiple ferroelectric phases, revealing the origin of the enhanced electrical properties in the PMN-PH-PT ceramics.

High Curie temperature (TC) xBi(Ni1/2Ti1/2)O3-(1-x)Pb(Zr1/2Ti1/2)O3 (xBNT-(1-x)PZT, BNT-PZT) piezoelectric ceramics were prepared by the conventional ceramic processing. The composition-induced morphotropic phase boundary (MPB) and its influences on structure and electrical performance were investigated. The synthesized BNT-PZT ceramics exhibit rather pure perovskite structure, and densified microstructure morphology with uniform elementals distribution in both grains and grain boundaries. With increasing the content of Bi(Ni1/2Ti1/2)O3 (BNT), crystal structure of the BNT-PZT ceramics transform from tetragonal phase to rhombohedral phase, and dielectric response peaks change from narrow shape to very broad shape but all presenting dielectric frequency dispersion. The diffused and relaxation dielectric behavior can be fitted well by the quadratic law, and the Vogel-Fulcher law fitting provides additional information on the relaxation characteristic. The MPB effects are confirmed further by ferroelectric and piezoelectric properties measurements. High-TC combined with excellent piezoelectric performance can be realized in the BNT-PZT system, which presents promising applications in geothermal exploration, aerospace and related elevated temperatures fields.

In present work, a multifunctional piezoelectric/photoluminescence effect, which originated from the combination of the piezoelectric properties and the photoluminescence effect, was realized in one-dimensional Er 3 + doped lead-free BaTiO 3 nanofibers prepared by a sol-gel based electrospinning method. The X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) were utilized to characterize the morphologies and phase structures. The effect of the host crystallization and rare-earth concentration on the structure and photoluminescence properties was studied. In addition, temperature-dependent PL spectrum exhibited a piezoelectric/photoluminescence coupling effect, characterized by the enhanced photoluminescence intensity around the ferroelectric-paraelectric phase transition temperature of BaTiO 3 .

The high-Curie temperature (TC) 0.15Pb(Mg1/3Nb2/3)O3-0.38PbHfO3-0.47PbTiO3 (PMN-PH-PT) piezoelectric ceramics were prepared via the citrate method. The rather homogeneous microstructure with nm-scale particles of the PMN-PH-PT precursor powders were attained with a calcining temperature ranging from 650 °C to 800 °C and pure perovskite structure of the PMN-PH-PT ceramics were prepared by the citrate method sintered from 1225 °C to 1265 °C. The content of the rhombohedral phase in the PMN-PH-PT ceramics sintered at 1245 °C increases first and then decreases with elevating the calcining temperature, and all the synthesized PMN-PH-PT ceramics have high density. The PMN-PH-PT ceramics exhibit complex dielectric behavior, in which the PMN-PH-PT ceramics calcined at 800 °C and sintered at 1245 °C exhibit the best dielectric properties with em = 26269 and TC/Tm = 297 °C. The nonlinear dielectric behavior of the PMN-PH-PT ceramics was successfully studied by the Rayleigh relation, which also reveals a polymorphic phase transition (PPT) resulted from the polar nanoregions (PNRs) in the PMN-PH-PT ferroelectric ceramics. Due to the mutual influences of grain size, domain configuration and microstructure morphology, the electrical properties of the synthesized PMN-PH-PT ceramics are influenced greatly, in which the PMN-PH-PT ceramics calcined at 775 °C and sintered 1245 °C exhibit the optimum ferroelectric and piezoelectric properties. The piezoelectricity of the PMN-PH-PT ceramics is superior to the same compositional ceramics synthesized by the columbite precursor method, which can be attributed to the morphotropic phase boundary (MPB) effect and densified microstructure induced by the wet-chemical citrate method. The PMN-PH-PT ceramics prepared by the citrate method exhibit excellent thermal stability of the piezoelectric and ferroelectric properties surpassing the common usage temperatures, indicating their promising transducer applications under elevated environmental temperatures.

(100)-oriented epitaxial relaxor ferroelectric 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-0.3PT) thin film was prepared on SrRuO3-buffered SrTiO3 single-crystal substrate by pulsed laser deposition. The phase and domain structure, ferroelectric and piezoelectric properties, and leakage current behavior were studied. Results indicated well saturated polarization-versus-electric field hysteresis loops with large remnant polarization of 30 µC/cm2 and coercive field of 11 kV/mm was obtained. The analysis on the leakage current behavior proposed that linear ohmic conduction and Fowler–Nordheim tunneling were the dominant mechanism for the electric field amplitude below and above 15 kV/mm, respectively. Furthermore, the epitaxial PMN-0.3PT thin film exhibited excellent local piezoelectric response and in situ electric-field-induced domain switching behavior. These results suggest the potential applications of the present epitaxial PMN-0.3PT film in integrated ferroelectric devices.

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.

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.

The pyroelectric properties of Mn-doped Aurivillius ceramics with different pseudo-perovskite layers were investigated. The pyroelectric coefficients for 0.2wt% Mn-doped two-layer CaBi2Nb2O9 (CBN-Mn), three-layer Bi4Ti2.85Nb0.15O12 (BTN-Mn), and four-layer CaBi4Ti3.95Nb0.05O15 (CBTN-Mn) ferroelectric ceramics were found to be on the order of 26.0, 54.4, 84.4 μC/m2K at room temperature, respectively. These values were closely associated with the number of octahedral layers in the pseudo-perovskite blocks. The high pyroelectric coefficient, together with low dielectric permittivity and loss (tanδ 660 °C) make the Aurivillius ceramics potential candidates for pyroelectric devices over a broad temperature range. This article is protected by copyright. All rights reserved.

In this work, a high-frequency lead-free ultrasonic transducer was designed and fabricated based on high-performance (K 0.44 Na 0.56 )NbO 3 -0.5 mol%Mn (Mn-KNN) piezoelectric single crystal. 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 ∼20 MHz medical ultrasonic transducer with an optimized bandwidth up to 85.1% was obtained. The experimental results exhibited a center frequency of 20.9 MHz with −6 dB bandwidth of 65.3%. The excellent acoustic performance makes this lead-free single-crystal transducer potential for practical applications.

The 0.55Pb(Ni 1/3 Nb 2/3 )O 3 -0.05PbHfO 3 -0.4PbTiO 3 /Ni 0.875 Zn 0.125 Fe 2 O 4 (PNNHT/NZF) 0–3 particulate composite ceramics were prepared by the conventional solid-state reaction method via introducing the nano-sized WO 3 and CuO sintering aids by the self-combustion method. Due to the introducing of nano-sized sintering aids, densified PNNHT/NZF composite ceramics are synthesized sintered at low sintering temperature. Furthermore, the nano-sized sintering aids act effectively as blocking layers, leading to compact composite ceramics with homogenously dispersed and isolated microstructure morphology, inhibiting inter-phase diffusion, avoiding interfacial chemical reaction, and achieving strong inter-phase coupling. Therefore, the synthesized PNNHT/NZF composite ceramics exhibit enhanced magnetoelectric properties.

Er3+-doped Na0.5Bi0.5TiO3 (Er-doped NBT) ceramics were prepared via a hydrothermal method. High sintering active Er-doped NBT nano cubic particles with perovskite structure were synthesized at hydrothermal condition of 200 °C for 24 h in 12 M NaOH solution, which were self-assembled via in situ crystallization mechanism by the initially as-grown nanowires. The Er-doped NBT ceramics sintered at 1100 °C for 2 h exhibit pure rhombohedral perovskite structure, high densification and rather homogenous microstructure morphology. Under 488 nm light excitation, the strong green emission peaks centering at 530 nm and 550 nm and the weak red emission peaks locating at 665 nm and 735 nm are excited, which can be attributed to the 2H11/2, 4S3/2, 4F9/2 and 4I9/2 → 4I15/2 transitions, respectively. The maximum emission intensity is obtained when the Er doping content reaches 1.0 mol%. A strong upconversion emission peak centering around 550 nm in green light range is excited under 800 nm light excitation, which is correlated with the 4S3/2 → 4I15/2 transition.

Ferroelectric phase transition characteristic and electrical conduction mechanism of the high Curie-point (TC) 0.15Pb(Mg1/3Nb2/3)O3−0.4PbHfO3−0.45PbTiO3 (PMN-PHT) piezoelectric ceramics were studied by the temperature dependent Raman spectra and electrical properties. Sole first-order ferroelectric phase transition is demonstrated by the thermal hysteresis behavior of the temperature dependent dielectric constant and the dramatic drop of the derivative of inverse dielectric constant ξ= d(1/er)/dT around TC in the PMN-PHT ceramics. The temperature dependent Raman spectroscopy not only provides further evidence for the ferroelectric to paraelectric phase transition appearing around TC in the PMN-PHT ceramics, but also reveals the successive phase symmetry changes of the polar nanoregions (PNRs), in which apparent anomalies appear in the Raman peaks' wavenumber, wavenumber distance, intensity, intensity ratio, and line width of some selected Raman modes upon heating. Typical sole cole-cole circle is obtained for the PMN-PHT ceramics in the temperature range of 440–560 °C, based on which the activation energy (Ea) of the electrical conduction is calculated being ~1.2 eV. Such low value of Ea indicates that the oxygen vacancies formed in the PHT-PMN ceramics induced by the evaporation of Pb during the sintering process dominate the high-temperature extrinsic electrical conduction.

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.

$(\mathrm{N}{\mathrm{a}}_{1/2}\mathrm{B}{\mathrm{i}}_{1/2})\mathrm{Ti}{\mathrm{O}}_{3}\text{\ensuremath{-}}x\mathrm{BaTi}{\mathrm{O}}_{3}(\mathrm{NBT}\text{\ensuremath{-}}x\mathrm{BT})$ single crystal, as one of the most promising candidates to replace lead-based ferroelectrics, is a typical and unique lead-free system with morphotropic phase boundary (MPB) by far. In this paper, the phase transition process of NBT-0.06BT crystal in a wide temperature range of $20\ensuremath{\sim}550{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ was analyzed at atomic scale by theoretical fitting to the measured synchrotron radiation x-ray absorption fine structure spectra quantitatively. Detailed analysis revealed a gradually transition of local structure at the point of phase transition from rhombohedral to tetragonal phase in NBT-0.06BT crystal on the bond lengths of Bi-O and Bi-Ti. The continuous evolution of local structure with no obvious barrier to overcome is one of the intrinsic characteristics of MPB at atomic scale and is responsible for the high piezoelectric properties. These results could promote the understanding of the origin of the high piezoelectric performance around the MPB and meanwhile guide new lead-free material designs.

Perovskite oxides with luminescent ions hold great promise in optoelectronic devices because of their outstanding thermal stabilities and electro-optic performance. As one typical perovskite upconversion (UC) host material, lead-free potassium sodium niobate ((K, Na)NbO3/(KxNa1-x)NbO3 or KNN) has attracted much attention in recent years. In the present work, a novel routine was developed to tune the upconversion photoluminescence (UC PL) performance by controlling the oxygen vacancy concentration in the KNN matrix, based on the 0.1% Er3+-doped KNN (Er-KNN) single crystals grown for the first time. UC PL properties, conductivity and defect chemistry of the single crystals were systematically investigated. The UC PL intensity of the as-grown Er-KNN material could be enhanced by 20 times after oxygen atmosphere annealing at 800 °C and fully quenched after vacuum annealing. What's more, by annealing under an oxygen atmosphere and vacuum, the conductivity of the Er-KNN sample was successfully tuned for more than 8 orders of magnitude. The super-wide range tunability of UC PL performance and conductivity could be explained by oxygen vacancies which gave rise to Nb5+-Nb4+ valence alternation. Because of the modulated photoluminescence properties and conductivity, our grown Er-KNN single crystals have great potential for use in multifunctional devices.

High-Curie temperature relaxor ferroelectric single crystals attracted attention recently due to the excellent global electrical properties for electromechanical devices. In this work, the electrical properties, domain structure, and local piezoelectric response of ternary 0.3Pb(In1/2Nb1/2)–0.4Pb(Mg1/3Nb2/3)–0.3PbTiO3 (0.3PIN-0.4PMN-0.3PT) single crystal was investigated. Large electric field-induced strain with little hysteresis was obtained in -oriented high-quality crystal. Nanosized fingerprint pattern domain of ~ 100–300 nm with obvious local piezoelectric response was observed. The temperature-dependent dielectric spectrum revealed a ferroelectric rhombohedral to tetragonal phase transition at 106 °C, obviously higher than that of binary 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 single-crystal (~80 °C). The evolution of the ferroelectric property and strain response was also studied at elevated temperature. The temperature dependence of the PFM results demonstrated that the surface domain structure of the 0.3PIN–0.4PMN–0.3PT single crystals could still be detected above the Curie temperature. The local piezoelectric hysteresis loop exhibited strong dependence on the DC bias field and obvious local butterfly shape displacement curve could be induced at 180 °C under larger local DC field.

LiCaAlF6 single crystals doped with different Eu concentrations varied from 1 at% to 5 at%, and LiCaAlF6:Eu single crystals co-doped with 3 at%Cu+, 2 at%Mg2+, 2 at%Ba2+ were grown by the Bridgman method in non-vacuum atmosphere. Their optical and scintillation performances were studied. The optimal scintillation efficiency was achieved in the LiCaAlF6:Eu single crystals with Eu concentrations between 2 and 2.5 at%. The influences of Cu+, Mg2+ and Ba2+ co-doping on optical properties, scintillation yield, scintillation decay and defect structures were studied. It was found that the Cu+ co-doping can improve the scintillation efficiency. The Mg2+ and Ba2+ co-doping have negligible effects on light yield.

Ferroelectric single crystals Mn-doped 0.29Pb(In 1/2 Nb 1/2 )O 3 -0.31Pb(Mg 1/3 Nb 2/3 )O 3 -0.40PbTiO 3 (Mn-PIMNT) have been grown by a modified Bridgman technique. The as-grown ternary tetragonal Mn-PIMNT (29/31/40) single crystals exhibit ultra-high Curie temperature T C of 216 °C, 110 °C higher than that of Mn-PMNT(72/28) single crystals( T d ∼ 105 °C). In addition, the permittivity e r of tetragonal Mn-PIMNT(29/31/40) is 350 at 1 kHz, approximately less than that of Mn-PMNT(72/28)( e r ∼ 640) in half. Moreover, as a core parameter of pyroelectric material, the figure of merits for detectivity ( F d ) for Mn-PIMNT(29/31/40) is 23.5 × 10 −5 Pa −1/2 , close to that of Mn-PMNT(72/28)( F d ∼ 28.5). Finally, outstanding Mn-PIMNT(29/31/40) based pyroelectric detectors were fabricated, of which the specific detectivity ( D *) (room temperature, 10 Hz) is up to 1.74 × 10 9 cmHz 1/2 /W for current-mode detectors, and 1.15 × 10 9 cmHz 1/2 /W for voltage-mode detectors, 3 times higher than that of commercial LiTaO 3 based detectors. All of these results make these ternary tetragonal Mn-PIMNT single crystals a promising candidate for infrared detector applications.

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 compositi...

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.

In situ temperature dependent ferroelectric domains dynamic evolution of the (001) pc oriented 0.91Pb(Zn 1/3 Nb 2/3 )O 3 -0.09PbTiO 3 (PZNT91/9) single crystals was observed by polarized light microscopy (PLM) and real time synchrotron-radiation (SR) X-ray white-beam topography. Intricate domain structures including monoclinic phase are distinguished by PLM at room temperature, and irreversible domain configuration dynamic evolution upon thermal cycling is observed by both methods. Such irreversible domain evolution combined with coexistence of multi-phases and polarization rotation may be related to the extraordinary piezoelectric performance in the ferroelectric single crystals with the morphotropic phase boundary (MPB) compositions.

Lead-free (K0.44Na0.46)NbO3-0.5%MnO2 (KNN-0.5%MnO2) single crystals with dimensions of Ф30×10 mm were successfully grown by a top seeded solution growth technique (TSSG). The X-ray diffraction pattern has shown that the as-grown crystals have an orthorhombic perovskite structure. The orthorhombic-tetragonal (TO-T) and tetragonal-cubic phase transition temperature (the Curie temperature TC) of the single crystal were found at 184 °C and 412 °C, respectively. The KNN-0.5%MnO2 single crystals exhibited high piezoelectric constants d33 and dielectric permittivity er, being 261 pC/N and 275. Well saturated P-E hysteresis loop with remnant polarization Pr=22.06 µC/cm2 and coercive field Ec=17.93 kV/cm was obtained at a maximum electric field of 3 kV/mm. A high strain (0.24%) and electromechanical coupling coefficient Kt (65.9%) were obtained along the (001) orientation. These excellent results indicated that the KNN-0.5%MnO2 single crystals could be used as high quality lead-free material.

Growth and quality of single crystals are unusually sensitive to the thermal distribution. In the appropriate thermal field ferroelectric single crystal 23Pb(In 1/2 Nb 1/2 )O 3 –44Pb(Mg 1/3 Nb 2/3 )O 3 –33PbTiO 3 (abbr. PIN–PMN–PT, or PIMNT), with 105 mm in diameter and 150 mm in length, is successfully grown by the modified Bridgman technique. This as-grown crystal shows excellent properties ( k 33 ~0.92, d 33 ~2200 pC/N, E c ~5.7 kV/cm, T c ~185 °C, T r/t ~120 °C; k t ~0.60) near morphotropic phase boundary. In order to suppress the compositional segregation and improve the crystal quality, the controllable orientation growth for specific applications is performed successfully using the same oriented seed. For magnetoelectric applications as-grown oriented PIN–PMN–PT crystal demonstrates its high homogeneity (Δ e δ T r / t T c k t Φ 80 mm transverse wafer). These results of single crys t al PIN–PMN–PT will greatly meet demands of its devices and promote its applications in the future.

A sensitive chip with ultralow dielectric loss based on Mn doped PMNT (71/29) has been proposed for high-end pyroelectric devices. The dielectric loss at 1 kHz is 0.005%, one order lower than the minimum value reported so far. The detective figure of merit (Fd) is up to 92.6 × 10−5 Pa−1/2 at 1 kHz and 53.5 × 10−5 Pa−1/2 at 10 Hz, respectively. In addition, an inverted pyramid suspending architecture for supporting the sensitive chip has been designed and manufactured by 3D printing technology. The combination of this sensitive chip and the proposed suspending architecture largely enhances the performance of the pyroelectric detectors. The responsivity and specific detectivity are 669,811 V/W and 3.32 × 109 cm Hz1/2/W at 10 Hz, respectively, 1.9 times and 1.5 times higher than those of the highest values in literature. Furthermore, the microphonic effect can be largely inhibited according to the theoretical and experimental analysis. This architecture will have promising applications in high-end and stable pyroelectric infrared detectors.

In this paper both linear and nonlinear magnetoelectric (ME) effects have been investigated intensively. In order to obtain magnetic amplification, we fabricated 3 multi-push–pull mode magnetoelectric laminated composites metglas/PMNT/metglas based on dumbbell-shaped metglas. The linear magnetoelectric charge coefficient is enhanced to 2600 pC/Oe at 2 Hz based on dumbbell-shaped metglas and it increases as the end-flange width of the dumbbell-shaped metglas increases at 2 Hz, respectively. Based on these 3 ME composites, we establish an active mode nonlinear modulation system for ME magnetic sensor, the sensitivity of which are enhanced to 80, 100 and 102 pT / √ Hz at 1 Hz for the composites with the end-flange width 20, 15 and 10 mm, respectively, via nonlinear ME modulation method. Strain distribution simulations illustrate the theoretically accurate amplification of the dumbbell-shaped geometry. The center strains of 3 dumbbell-shaped metglas decrease as the width of end-flanges decreases

Due to its higher frequency, improved impedance matching, and easy formation of array, piezoelectric micromachined ultrasonic transducer (PMUT) has drawn much attentions for application in ultrasound imaging. In this paper, PMUT based on [011] poled 0.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO3 (PMN-0.30PT) single crystal thin film was proposed and modeled by performing finite element method. Influences of different configurations of top electrode shape and bottom cavity shape on PMUT performance were studied. The investigation results show that the resonant frequency of PMN-PT-based PMUT with circular top electrode and square bottom cavity is up to 27.155 MHz. The effective electromechanical coupling coefficient ( k eff 2 ) of PMUT was up to 2.32%, which was 127% larger than that of lead zirconate titanate-based PMUT. The static transmitting sensitivity was three times enhancement compared to PMUT with square top electrode and square bottom cavity. Furthermore, acoustic field characteristics of PMUT and PMUT arrays based on PMN-PT in water were investigated. The relative pulse-echo sensitivity level of 2 × 2 PMUT array was −35 dB with the reflector at 200 μm. The obtained results demonstrated that the proposed PMN-PT-based PMUT can achieve high frequency and large k eff 2 as well as considerable sensitivity, which is promising for application in high resolution ultrasound imaging.

In this paper, we present hetero acoustic layer (HAL) structures based on ScAlN thin films with a c-axis tilt angle. The surface acoustic wave (SAW) excitation modes and their propagation characteristics for different Euler angles (0°, θ, ψ) of the ScAlN thin film are analyzed using the finite element method. We find that the acoustic field distribution of HAL structures can be adjusted by rotating their Euler angles and that normal SAWs are suppressed; however, leaky SAWs (LSAWs) with significantly improved electromechanical coupling coefficients (K 2) are excited. A maximum K 2 of 14% can be obtained for shear horizontal (SH)-type LSAWs, which is almost 7 times larger than that of the previously reported normal SAW Sezawa mode. Moreover, the optimized HAL structure consisting of (0°, 90°, 60°) ScAlN thin film/SiO2/AlN/Si simultaneously possesses a larger K 2, a wider bandwidth, and a higher Q value, which is promising for the design and application of wideband SAW devices with high performance.

Pressure evolution of local structure and vibrational dynamics of the perovskite-type relaxor ferroelectric single crystal of 0.935(Na0.5Bi0.5)TiO3-0.065BaTiO3 (NBT-6.5BT) is systematically investigated via in situ Raman spectroscopy. The pressure dependence of phonon modes up to 30 GPa reveals two characteristic pressures: one is at around 4.6 GPa which corresponds to the rhombohedral-to-tetragonal phase transition, showing that the pressure strongly suppresses the coupling between the off-centered A- and B-site cations; the other structural transition involving the oxygen octahedral tilt and vibration occurs at pressure ∼13–15 GPa with certain degree of order-disorder transition, evidenced by the abnormal changes of intensity and FWHM in Raman spectrum.

In this paper, we reported the fabrication and high acoustic performance of high frequency needle ultrasound transducer based on 0.70Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 single crystal/Epoxy 1–3 piezoelectric composite, which was prepared by using the dice and fill (DAF) method. The as-prepared 0.70PMN-0.30 PT/Epoxy 1–3 composite has high thickness extension mode electromechanical coupling coefficient with the value of 67.3 %. The transducer is designed by PMN-PT/Epoxy 1–3 piezoelectric composite with a dimension of 550 μm × 450 μm × 35 μm. The fabricated transducer has not only a high center frequency larger than 42 MHz, but also high bandwidth of -6 dB of 90.6 %, the insertion loss with the value of 16 dB and excellent transmitting sensitivity of 314 mV/V. The results are in good agreement with the values simulated by PiezoCAD software. In addition, the acoustic performance of the transducer was also obtained by measuring the acoustic filed distribution in purified water. The -3 dB acoustic beam dimension width, the value of focal length and the acoustic power were 0.38 mm × 0.42 mm, 2.3 mm and 4.4 × 10−3mW, respectively. The performance PMN-PT/Epoxy 1–3 piezoelectric composite ultrasound transducer fabricated by dice and fill method (DAF) achieved the effect of ultrasonic transducer fabricated by deep reactive ion etching (DRIE). The excellent acoustic performance demonstrated that the DAF prepared PMN-PT/Epoxy 1–3 piezoelectric composite have great industry application potential in high frequency ultrasonic electronics, such as microelectronics NDT and biomedical imaging.

This paper presents a bio-inspired cantilever-type SAW pressure sensor based on Scandium-doped AlN (ScAlN)/3CSiC/Si layer structure. The proposed biomimetic microcantilever is configured with stress concentration region (SCR) comprising of a series of narrow slits. For a given depth, by properly setting the number and the width of those slits for a given depth, homogeneous stress/strain distribution in vicinity of SCR are achieved. Furthermore, multi-physics finite element modeling for evaluating the pressure coefficient of frequency (PCF) of a one-port SAW resonant sensor is performed and validated. Then the PCF for the proposed SAW pressure sensor with the optimized biomimetic microcantilever is analyzed. The dependence of ScAlN thin film thickness h ScAlN and scandium-doped concentration r of Sc r Al1-r N thin film on PCF for different SAW modes including Rayleigh mode and Sezawa mode are calculated. The investigation results show that the maximum PCF of −111 ppm bar−1 can be achieved for Rayleigh mode, which is 2.4 times larger than that of the previously reported ZnO/Si structure. In addition, its PCF has weak dependence on h ScAlN, which are quite favorable for manufacturing pressure sensors with good reproducibility. The conceived bio-inspired cantilever-type SAW devices based on ScAlN/3 CSiC/Si structure will open the door to develop pressure sensors with a stable and reliable performance and enhanced sensitivity.

Antiferroelectric analogous (Pb0.92Sr0.05La0.02)(Zr0.7Sn0.25Ti0.05)O3 (PSLZSnT) ceramics were prepared by the solid-state sintering method by introducing a Y2O3-coating via the self-combustion method. The synthesized Y2O3-doped PSLZSnT ceramics present pseudo-cubic structure and rather uniform microstructural morphology accompanied by relatively small grain size. Excellent energy-storage performance is obtained in the Y2O3-doped PSLZSnT ceramics, in which the value of the energy-storage density presents a linearly increasing trend within the electric field measurement range. Such excellent performance is considered as relating to the rather pure perovskite structure, high relative density accompanied by relatively small grain size, and the antiferroelectric-like polarization-electric field behavior.

Antiferroelectric analogous (Pb0.92Sr0.05La0.02)(Zr0.7Sn0.25Ti0.05)O3 (PSLZSnT) ceramics were prepared by the solid-state sintering method by introducing a Y2O3-coating via the self-combustion method. The synthesized Y2O3-doped PSLZSnT ceramics present pseudo-cubic structure and rather uniform microstructural morphology accompanied by relatively small grain size. Excellent energy-storage performance is obtained in the Y2O3-doped PSLZSnT ceramics, in which the value of the energy-storage density presents a linearly increasing trend within the electric field measurement range. Such excellent performance is considered as relating to the rather pure perovskite structure, high relative density accompanied by relatively small grain size, and the antiferroelectric-like polarization-electric field behavior.

Poling method is very important for ferroelectric and piezoelectric materials and their applications. We propose an interdigitated (ID) electrodes geometry and screen-print the ID electrodes on cut 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 plates. However, it is very hard to pole the piezoelectric phase without cracks, resulting in high dielectric loss and high dielectric noise in corresponding sensors, which should be avoided in ME magnetic sensor devices. Because there appears a malformed region between longitudinal beams and tips of transverse electrodes. In this paper, we propose and adopt high temperature poling technique to reduce the strain and internal stress to reduce cracks. Strain-temperature curve of PMN-PT has a peak at 100 °C and strain at 140 °C (0.32%) is less than ½ of that at 100 °C (0.66%) under the same tested voltage (1000 V/mm). The noise equivalent magnetic induction (NEB) numerical simulation indicates that ME composite with high temperature poled PMN-PT (140 °C) has the lowest NEB, demonstrating that high temperature poling technique can lower dielectric loss and enhance ME effect by improving piezoelectric effects gently.

A distributed electrode structure of sensitive element based on Mn-doped Pb(Mg 1/3 Nb 2/3 )O 3 -0.29PbTiO 3 single crystals for high-end pyroelectric infrared detectors has been proposed, demonstrating a notably superior pyroelectric response. Under the optimal electrode distance of 0.5 mm, the figure of merit for detectivity is up to 39.9 × 10 −5 Pa −1/2 . An ultrahigh responsivity of 864 V/W and specific detectivity of 1.49 × 10 9 cm Hz 1/2 /W at 10 Hz are observed, approximately 3.6 and 1.4 times higher, respectively, than that of the conventional faced electrode structure. The enhanced responsivity and specific detectivity of the distributed electrode structure will make PMNT based detectors with voltage mode promising in practical use of sensors.

In order to improve the applicability of Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) single crystal and make full use of relaxor ferroelectric single crystal based array transducer on high frequency, PIN–PMN–PT/epoxy 2–2 composite with the width-to-height ratio G of 0.5 in single crystal beam was prepared by a dice-and-fill method. Excellent properties for the fabrication of ultrasonic transducer has been achieved, where ultrahigh thickness electromechanical coupling coefficient (kt), ultrahigh effective electromechanical coupling coefficient (keff), relatively high piezoelectric constant (d33), and low acoustic impedance (Z) are 86%, 88.4%, 1200 pC/N and 21 MRayls, respectively. Based on the improved flexibility of as-prepared PIN–PMN–PT/epoxy 2–2 composite, a 12-element array transducer with the center frequency of 10 MHz has been designed, fabricated and characterized. The high frequency array transducer has achieved an ultra-broad bandwidth (@-6 dB) of 127.7%. It is worth mentioning that all 12 elements in the array work very well. The array transducer based on PIN–PMN–PT/epoxy composite exhibits excellent uniformity, confirming that the relaxor ferroelectric single crystal based 2–2 composite can be used to develop high-performance array transducer in the field of high frequency application.

In this paper, a magnetoelectric laminate composite based on length magnetized Metglas and length-polarized ternary 0.35Pb(In 1/2 Nb 1/2 )O 3 –0.35Pb(Mg 1/3 Nb 2/3 )O 3 –0.30PbTiO 3 (PIMNT) single crystal has been presented. This Metglas/PIMNT L–L mode composite exhibits ultrahigh magnetoelectric voltage coefficients of ∼17 V/Oe at quasi-static frequency and of ∼147 V/Oe at resonance frequency, which are much larger than other magnetoelectric composites reported so far. Analysis of magnetic field sensitivity indicates that the estimated noise equivalent magnetic induction of the proposed composite is as low as 8.6 pT/Hz 1/2 @1 Hz. Due to its giant magnetoelectric voltage coefficients, the maximum magnetic-field-energy-harvesting output power reaches 29.2 mW/Oe 2 , which is about 3.65 times than that of previously reported Metglas/PMNT multi-push–pull mode composite. Accordingly, the proposed Metglas/PIMNT L–L mode composite shows promising applications in magnetic field detection sensors as well as transducers for magnetic field energy harvesting.

1 mol% Sr and 1 mol% Sn co-doped (Ba 0.84 Ca 0.15 Sr 0.01 )(Ti 0.90 Zr 0.09 Sn 0.01 )O 3 (BCSTZS) ceramics were prepared by the conventional solid-state reaction method. The sintered BCSTZS ceramics exhibit pure perovskite structure with composition locating at the rhombohedral side around the morphotropic phase boundary (MPB) of the BCZT system. With the increase of sintering temperature, the grains grow up, porosity eliminates and microstructure becomes dense accompanied by the improvement of electrical properties of the synthesized BCSTZS ceramics. Although the grain size of the BCSTZS ceramics sintered at elevated temperatures is rather “small”, they still exhibit excellent electrical properties, which can be attributed to the MPB effect and the dense microstructure induced by the Sr and Sn co-doping. The BCSTZS ceramics sintered at 1550 °C exhibit improved thermal stability of the piezoelectric and ferroelectric properties within the common usage temperatures, indicating that the BCSTZS ceramics are promising lead-free candidates for the widely used lead-based piezoelectric materials.

A new relaxor-based ferroelectric ternary system Pb(Lu 1/2 Nb 1/2 )O 3 –Pb(Mg 1/3 Nb 2/3 )O 3 –PbTiO 3 (PLN–PMN–PT), with a combination of a high-Curie temperature system Pb(Lu 1/2 Nb 1/2 )O 3 –PbTiO 3 (PLN–PT) and a high piezoelectricity system Pb(Mg 1/3 Nb 2/3 )O 3 –PbTiO 3 (PMN–PT), was investigated in this paper. Single crystal PLN–PMN–PT with dimensions of Φ20×45 mm 3 was grown successfully by the modified Bridgman technique for the first time. The studies of structure and composition of the as-grown crystal showed structural consistency but compositional deviation along the growth direction. The 〈0 0 1〉-oriented wafers of the PLN–PMN–PT single crystal showed excellent electrical properties at room temperature: e 33 ~4500, tan δ ~0.5%, d 33 ~2300 pC/N. The crystal was found to exhibit high Curie temperature ( T C ~176°C), rhombohedral–tetragonal phase transition temperature ( T RT ~108 °C) and coercive field ( E C ~8.1 kV/cm), superior to those of PMN–0.3PT single crystal. Studies of temperature dependence ferroelectric properties showed that high values of k 33 and d 33 could be maintained up to the T RT . These results showed that PLN–PMN–PT piezoelectric single crystal has a higher Curie temperature and coercive field with excellent electrical properties, making the crystal a promising candidate for high-power transducer applications in a broad temperature range.

xPb(Mg1/3Nb2/3)O3-yPbZrO3-(1-x-y)PbTiO3 (PMN-PZ-PT) ferroelectric ceramics were prepared by the conventional ceramic processing via a B-site oxide mixing route. Complete solid solutions can be formed for PMN-PZ-PT in the whole composition range studied, which exhibits pure tetragonal, morphotropic phase boundary (MPB) or rhombohedral perovskite structure depending on compositions. Enhanced structure and electrical performance detected by XRD measurement, and dielectric, ferroelectric and piezoelectric properties characterization confirm the MPB effect. Such phenomena correspond well with the composition-induced successively structural change from rhombohedral, across MPB, and to tetragonal perovskite structure with the increase of the PbTiO3 content. The preliminary composition phase diagram of the PMN-PZ-PT system is determined by XRD measurement combining with electrical properties characterization. The mechanisms of the structure and electrical properties enhancement are related to easy paths with flat...

A series of (Na0.5Bi0.5)TiO3–PbTiO3 (NBT–PT) single crystals with compositions near the morphotropic phase boundary (MPB) region were grown by the modified Bridgman technique. The dependence of structure on composition was measured, and the MPB region of the NBT–PT system was confirmed. The dielectric properties of the NBT–PT single crystals were investigated, and the phase transition behaviour of the NBT–PT single crystals during heating was examined. With increasing addition of PT, the coercive field of the NBT–PT crystals decreased to levels much lower than that of the pure NBT system; such a change allowed easy poling of the NBT–PT crystals and the resultant piezoelectric properties were significantly enhanced. The electromechanical coupling factor of the crystals showed relatively constant thermal stability at the depolarization temperature (Td). Finally, studies of the domain evolution of NBT–0.09PT showed the disappearance of domains at the Td, which indicates that phase transition at the Td is related to changes in domain structures.

Ternary ferroelectric single crystal Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) was grown by the modified Bridgman method. The compositional variation of different regions of the crystals was measured, and the segregation regularity of the crystals was proposed. Variations in the dielectric properties and domain structures of the PIN–PMN–PT single crystals were investigated as a function of temperature and composition, and the phase transformation behavior of the crystals was observed. The PIN–PMN–PT crystals showed high Curie temperatures (T C = 160–210 °C), ferroelectric phase transition temperatures (T R–T up to 132 °C) and coercive fields (E C = 6–8 kV/cm) as well as excellent piezoelectric properties (d 33 up to 2,800 pC/N) and electromechanical coefficients (k 33 > 0.90). As the temperature increased, k 33 values remained relatively constant and d 33 increased gradually prior to ferroelectric phase transformation, and these results reflect the wide temperature usage range of PIN–PMN–PT single crystals. The polarization (P r ) and E C of the crystals showed unique trends during the phase transformation process; high P r and E C values can be maintained prior to depolarization, which indicates that the PIN–PMN–PT single crystals are candidate materials for high-power applications. In summary, PIN–PMN–PT single crystals with ultrahigh electric properties, large coercive fields and excellent thermal stability may potentially be applied in harsh environments.

The present work investigated the influence of the composition induced structure evolution on the electrocaloric effect in lead-free (0.935− x )Bi 0.5 Na 0.5 TiO 3 –0.065BaTiO 3 – x SrTiO 3 (BNBST, BNBST x ) ceramics. It was found that broad ∆ T peak could be observed for all compositions and the electrocaloric strength α ( α =Δ T max /Δ E ) in BNBST0.02 could reach as high as 0.27 K mm/kV. The increase of the SrTiO 3 concentration led to a shift of ∆ T max to a lower temperature, resulting in a large near room-temperature electrocaloric strength α of 0.17 K mm/kV in BNBST0.22.

The refractive indices, extinction coefficients, and transmittance of 1 mol% Mn-doped 0.15Pb(In1/2Nb1/2)O3–0.57Pb(Mg1/3Nb2/3)O3–0.28PbTiO3 (Mn-PIN–PMN–PT) relaxor-based single crystal were investigated. The Mn-PIN–PMN–PT single crystal exhibited a rhombohedral to tetragonal phase transition temperature Trt of 120.3 °C and Curie temperature TC of 152.4 °C. The improved Sellmeier equation for the refractive index was determined by least-squares method, which can be applied to calculate accurately the refractive index over a wide wavelength range from 350 to 5000 nm. The Sellmeier optical coefficients were found to be S0 = 1.178 × 1014 m−2, λ0 = 0.215 µm, E0 = 6.06 eV and Ed = 28.73 eV through fitting the single-term oscillator equation. The transmittance reached about 72% over a wide wavelength from 500 nm to 2.5 µm. The optical band-gap energy Eg of 3.34 eV was obtained from absorption coefficient spectra by use of the Tauc model. The results can offer essential parameters of the Mn-PIN–PMN–PT single crystal for optical device applications.

In this work, the time and temperature dependence of the piezoelectric and ferroelectric properties of the 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (0.7PMN–0.3PT) single crystals were investigated in order to search for an effective method to improve their properties further. The piezoelectric properties of the [001]-, [110]- and [111]-oriented 0.7PMN–0.3PT single crystals exhibit excellent time stability during the 2-month room-temperature aging process. The re-poling process leads to the improvement of piezoelectric constant d 33 for the [001]-, [110]- and [111]-oriented 0.7PMN–0.3PT single crystals, while the values of electromechanical coupling coefficient k t change little. During the thermal aging, the values of the measured d 33, calculated converse piezoelectric constant $$d_{33}^{*}$$ , maximum strain S max% and longitudinal electrostrictive coefficient Q of the [001]-, [110]- and [111]-oriented crystal plates increase gradually before the ferroelectric phase transition temperatures (T FPT, T R–M, T R–O and T R–T) and then decline continuously. The increase in these values before the T FPT is a result of the phase instability. In general, the [001]- and [110]-oriented 0.7PMN–0.3PT single crystals exhibit large piezoelectricity, excellent time stability and relatively high thermal stability between 20 and 80 °C, which is favorable to the piezoelectric applications.

In situ observations of the phase symmetry and domain evolution of (K0.25Na0.75)NbO3 single crystals under bipolar electric fields have been performed for both pseudocubic (110) and (001) orientations using polarized light microscopy and X-ray diffraction. The macroscopic symmetry was identified to be a monoclinic C type phase with the spontaneous polarization direction close to . The electric field-driven domain morphology and evolution model were also presented. It was found that, under an antiparallel electric field, the approximately 180° domain switching process in a pseudocubic (101) sample consists of three steps: two ~60° domain switching and a ~90° domain switching, and the ~90° domain switching process in the pseudocubic (001) sample is composed of two ~60° switching steps.