Narrow Results

A model of a novel 1–3-type composite containing two ferroelectric components is put forward. In this composite, ferroelectric single crystal (SC) rods and ferroelectric ceramic rods are distributed in a polymer matrix. For a lead-free 1–1–3 composite based on domain-engineered [Li_x(K${}_{1-y}$Na_y)${}_{1-x}$](Nb${}_{1-z}$Ta_z)O₃:Mn SC, effective piezoelectric coefficients $d_{3j}^{\ast }$ and $g_{3j}^{\ast }$ and energy-harvesting figures of merit (FOMs) $d_{3j}^{\ast }{g}_{3j}^{\ast }$ are studied taking an active influence of the ferroelectric components into account. In a new m–$m_c$ diagram, regions of volume fractions of SC (m) and ceramic ($m_c$) are determined where FOM $d_{33}^{\ast }{g}_{33}^{\ast }$ changes from $6\cdot 10^{-11}$ to $9\cdot 10^{-11}$ Pa${}^{-1}$. Effective parameters of the 1–1–3 and related 1–0–3 composites are compared, and consistency is shown. The large longitudinal piezoelectric coefficient $g_{33}^{\ast }$ and FOM $d_{33}^{\ast }{g}_{33}^{\ast }$ of the lead-free 1–1–3 composite are to be of interest in piezoelectric sensorics and energy harvesting.

Ternary piezoelectric ceramics Pb(In${}_{1∕2}$Nb${}_{1∕2}$)O₃–Pb(Mg${}_{1∕3}$Nb${}_{2∕3}$)O₃–PbTiO₃ (PIN–PMN–PT) exhibit excellent temperature stability and hold great potential for high-frequency and high-power applications. However, its piezoelectric performance is much lower than that of the famous binary Pb(Mg${}_{1∕3}$Nb${}_{2∕3}$)O₃–PbTiO₃ (PMN–PT) system. In this work, high-performance 15PIN–50PMN–35PT piezoceramics with piezoelectric coefficient $d_{33}$ of 700 pC/N, electromechanical coupling coefficient $k_p$ of 66% and high Curie temperature $T_C$ of $199^{\circ }$C were fabricated. Effect of Samarium (Sm) doping content on the ferroelectric, dielectric, electromechanical and piezoelectric properties and structures of 15PIN–50PMN–35PT piezoelectric ceramics were investigated, and results reveal that increasing the amount of Sm doping leads to a significant decrease of $d_{33}$, $k_p$, $T_C$ and other properties. This phenomenon is different from the previously reported results in Sm-doped binary PMN–PT ceramics. The room temperature and variable temperature phase structure and room temperature microstructure were studied to explain this phenomenon.

Pure and superstoichiometric modified by 2wt.% Bi₂O₃ and 2wt.% manganese oxide (Mn₂O₃) ceramic samples of the binary system 0.71BiFeO₃-0.29BaTiO₃ were fabricated using conventional ceramic technology by double solid-phase synthesis with following sintering. Mechanical activation of synthesized powders was carried out at the stage of manufacturing press powders prepared for sintering. X-ray analysis at room temperature showed that all studied ceramics have pseudo-cubic symmetry. Grain morphology, dielectric and piezoelectric properties of selected solid solutions were investigated. The modification increased the homogeneity of the material, dielectric constant and piezomodulus $d_{33}$ and also resulted in a decrease in the dielectric loss tangent. The highest piezoelectric coefficient $d_{33}=105$ pC/N was obtained. Dielectric characteristics of ceramics revealed ferroelectric relaxor behavior and region of diffuse phase transition from the paraelectric to ferroelectric phase in the temperature range of 740–770K.

The structural, dielectric and piezoelectric properties of (1 − x)PbZr_0.52Ti_0.48O₃–xBaFe_0.5Nb_0.5O₃ ceramic system with the composition near the morphotropic phase boundary were investigated as a function of the BaFe_0.5Nb_0.5O₃ content by X-ray diffraction (XRD), dielectric measurement and piezoelectric measurement techniques. Studies were performed on the samples prepared by solid state reaction for x = 0.10, 0.12, 0.14, 0.16, 0.18 and 0.20. The XRD analysis demonstrated that with increasing BFN content in (1 − x)PZT_−xBFN, the structural change occurred from tetragonal to the mixture of tetragonal and cubic phase. Changes in the dielectric behavior and piezoelectric properties were found to relate with these structural changes depending on the BFN contents.

First-principles calculations are performed, revealing a significant enhancement of the piezoelectric properties of wurtzite Zn${}_{36}$O${}_{36}$ upon the incorporation of a single Cu atom. Research has demonstrated that the piezoelectric constant $d_{33}$ reaches its maximum value at a doping concentration of 1.4% for Cu atoms. The lattice parameters a and c of Zn${}_{36}$O${}_{36}$ are decreased and the piezoelectric strain coefficient $d_{33}$ is increased by replacing one Cu atom in Zn${}_{36}$O${}_{36}$. It is found that elastic softening is the primary factor responsible for the increase of $d_{33}$ in Zn${}_{35}$Cu₁O${}_{36}$. By differential charge density analysis, it is found that the covalency between Cu–O bonds is lower than that of Zn–O bonds, and the covalent bonding characteristics are weakened. Bader charge analysis shows that the charge of Cu is higher than that of Zn, indicating a more significant ionic bonding feature than that of Zn. Thus, a weaker covalent and stronger ionic bond are considered to play an essential role in promoting elastic softening for ZnO, which eventually promotes a significant enhancement in piezoelectric properties.

Lead-free (Bi_0.5Na_0.5)_1-x-y-zBa_x(Bi_0.5Li_0.5)_ySr_zTiO₃ ceramics were prepared by an ordinary sintering method and their structure and piezoelectric properties have been studied. X-ray diffraction patterns show that Ba²⁺, Li⁺ and Sr²⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a solid solution with a pure perovskite structure and a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases is formed at 0.04 ≤ x ≤ 0.08 and z < 0.06. The content of Li⁺ has no obvious influence on the crystal structure of the ceramics. The ceramics situated within the MPB exhibit a lower coercive field E_c and a larger remanent polarization P_r. Because of the formation of the MPB, lower E_c and larger P_r, the ceramics with x = 0.06, y = 0.075 - 0.125 and z = 0-0.02 possess improved piezoelectric properties. The optimum d₃₃ (235 pC/N) and k_p (36.3%) are reached at x/y/z = 0.06/0.125/0.02 and 0.06/0.075/0.02, respectively. The deformed P–E loop is also observed near or above T_d.

High-quality piezoelectric (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ thick films with dense and homogenous microstructures were fabricated at a low sintering temperature (900°C) using a CuBi₂O₄ sintering aid. The 10 μm thick film exhibited a high longitudinal piezoelectric constant d_33,eff of 210 pC/N with estimated unconstrained d₃₃ value of 560 pC/N very close to that in the corresponding bulks. Such excellent piezoelectric effect in the low-temperature sintered (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ thick films is comparable to the case of lead-based PZT thick films, and may be a promising application in lead-free microdevices such as piezoelectric microelectromechanical systems (MEMS).

A new lead-free solid solution of (1–x)NaNbO₃-xBa_0.85Ca_0.15(Ti_0.9Zr_0.1)O₃ was prepared by a traditional sintering method and its phase transition, dielectric and piezoelectric properties were studied. Ba_0.85Ca_0.15(Ti_0.9Zr_0.1)O₃ diffuses into NaNbO₃ lattices to form a new solid solution with perovskite structure. The addition of Ba_0.85Ca_0.15(Ti_0.9Zr_0.1)O₃(x≥0.025) transforms NaNbO₃ from antiferroelectric to ferroelectric. The diffusive ferroelectric–paraelectric phase transition is induced in the ceramics with high concentration of Ba_0.85Ca_0.15(Ti_0.9Zr_0.1)O₃. The ceramics with x = 0.05–0.125 possess large P_r values of 18.6–25.5 μC/cm². A morphotropic phase boundary between tetragonal and orthorhombic phases is formed at 0.05 < x < 0.15, leading to a significant enhancement of piezoelectric properties. The ceramic with x = 0.125 situated near the morphotropic phase boundary exhibits the optimum piezoelectric properties: d₃₃ = 151 pC/N and k_p = 31.6%.

Relations between the microgeometry, piezoelectric sensitivity and piezoelectric anisotropy are studied in porous composite materials based on Pb(Zr, Ti)O₃ ceramics. Systems of micrographs of cuts being parallel and perpendicular to the polarization direction are first shown for the porosity range v_p = 0.05 - 0.57, and examples of microcracking at v_p = 0.57 are considered. Experimental data on longitudinal and hydrostatic piezoelectric coefficients and squared figures of merit are represented as functions of v_p, and nonmonotonic behavior of the piezoelectric anisotropy factor with increasing v_p is analyzed in the context of changes in the microgeometry. Experimental results are compared to those derived from approximation formulae for the related porous ceramic.

Lead-free multifunctional ceramics of Ba_0.85Ca_0.15Ti_0.9Zr_0.1O₃-x mol% Dy have been prepared by an ordinary sintering method and the effects of Dy₂O₃ doping on structure, piezoelectric, ferroelectric and photoluminescent properties of the ceramics have been studied. The ceramics possess a single phase perovskite structure. The grain growth of the ceramics is prohibited and the ferroelectric–paraelectric phase transition at T_C becomes more diffusive after the addition of Dy₂O₃. Dy₂O₃ doping improves the piezoelectricity of the ceramics and the optimal piezoelectric properties d₃₃ = 335 pC/N is obtained at x = 0.5. The addition of 2 mol% Dy enhances the photoluminescent properties of the ceramics and strong emissions at ∼ 478 nm and ∼ 575 nm are observed. Our study shows that the ceramics with low Dy₂O₃ levels exhibit simultaneously the strong piezoelectricity, ferroelectricity and photoluminescence and may have a potential application in mechano-electro-optic integration and coupling device.

The effect of processing methods and a composition of ferroelectric (FE) (piezoelectric) phases on forming a microstructure of a ceramic framework during poling is studied in a ceramic material of the composition Pb_0.85Ca_0.15-xCd_xTi_0.9Zr_0.1O₃. A transition from using the solid-phase method for the synthesis of powder of a particular phase to a method of bulk "chemical assembly" leads to a change in the mechanical strength of the bulk granular medium and intergranular boundaries therein. Depending on a relationship between mechanical strength parameters of the studied materials, on poling the samples with a particular composition, anisotropic piezo-active composite materials with various connectivities of Pb_0.85Ca_0.15-xCd_xTi_0.9Zr_0.1O₃ phases can be obtained. These materials are characterized by various combinations of electrophysical properties and demonstrate advantages over the known anisotropic PbTiO₃-type ceramics. The fracture of ceramic grains during the poling process can be intensified by introducing FE phases with the composition comprising Cd²⁺ ions with a smaller radius and a most deformability in comparison to the Ca²⁺ ion.

Envisaged through adding sintering additives to achieve low-temperature sintering preparation, in order to overcome the volatilization of sodium ions and potassium ions in the high-temperature preparation, so as to improve the density and electrical properties of KNN-based piezoelectric ceramics. This research uses traditional solid-state sintering technology, a high density, high properties lead-free piezoelectric ceramics, KNNSC-$x$, successfully prepared with sintering additives CuO. The modern test analysis of XRD and SEM shows that a moderate amount of CuO doped in the range of research can form a single perovskite structure of an orthorhombic structure, not found in any second phase, and can promote grain evenly growing and improve the sintering properties of KNN-based piezoelectric ceramics. The KNNSC-0.04 ceramics exhibit excellent electrical properties through various electrical tests such as $d_{33}$ = 238pC/N, $k_p$= 47%, ${𝜀}_r$= 1049, tan$\delta$= 2.4%, $P_r$ = 25.6 $\mu$C/cm², $E_C$ = 1.24 kV/mm, respectively. These test results show that the KNNSC-$x$ piezoelectric ceramics have great potential to be applied in middle- and low-voltage piezoelectric devices.

Polycrystalline (Bi_0.94-xDy_xNa_0.94)_0.5Ba_0.06TiO₃ ceramics (x = 0, 0.04, and 0.08, designated as BNBT6, BNBT6: 4Dy and BNBT6: 8Dy, respectively) were prepared by conventional high temperature sintering method. The X-ray diffraction patterns show pure perovskite structure with no secondary phases. Lattice parameters and unit cell volumes have decreased due to Dy₂O₃ substitution. SEM micrographs revealed denser samples (ρ_rel > 97%) with uniformly distributed grain sizes. The room temperature piezoelectric properties of Dy₂O₃ substituted sample at x = 0.04 were relatively higher: d₃₃ = 147 pC/N, k_p = 28% and Q_m = 128. The samples exhibited infinitesimal change in thickness (≈ 15 nm) to an applied voltage of 100 V, which could be utilized in actuator applications. Relaxor behavior and broad dielectric maxima with diffuse phase transition were observed. The value of RT dielectric constant has increased while dielectric loss was decreased due to Dy₂O₃ substitution. Conductivity in the materials obeys Jonscher's universal power law. The conductivity in the low frequency region is associated with short range translational hopping while it is associated with the reorientational hopping in the high frequency region. The charge carrier concentration term remained constant over the entire temperature range of (30–500°C).

Mn-doped 0.92(K_0.5Na_0.5)NbO₃–0.08LiNbO₃ (0.92KNN–0.08LN) lead-free piezoelectric ceramics have been prepared by a developed sol–gel routes using Nb₂O₅ as Nb source. Due to the high quality of gel precursor, Mn-doped 0.92KNN–0.08LN nanopowders with the mean particle size about 20 nm were obtained at 500°C. The addition of Mn can promote the densification of nanopowders effectively at 950°C, and also influences in a pronounced way both the crystal structure and microstructure of the materials. With the increase of the amount of Mn addition, 0.92KNN–0.08LN ceramics are transformed from dominant orthorhombic to coexistence of the orthorhombic and tetragonal phases, and the grain sizes are enhanced simultaneously. Optimized parameters, such as d₃₃ = 212 pC/N and k_p = 0.46, were achieved in 0.2 Mn-doped 0.92KNN–0.08LN systems, which are good candidate material for lead-free piezoelectric devices.

In order to clarify the Na/K ratios dependence of piezoelectric properties, (K_1-xNa_x)NbO₃ ceramics were prepared by conventional solid-state sintering at x = 0.4–0.6 with a smaller compositional interval (0.02 mol). The results demonstrate that the Na/K ratios have obvious effect on piezoelectric and ferroelectric properties of (K_1-xNa_x)NbO₃ ceramics. Piezoelectric and ferroelectric properties show the maximum (d₃₃ = 147 pC/N, k_p = 0.40, and P_r = 24 μC/cm²) at x = 0.54, which is not consistent with conventional viewpoint. The reasons should be attributed to the existence of a phase boundary at x = 0.54 mol, which is similar to the morphotropic phase boundary in Pb(Zr,Ti)O₃ ceramics.

Solid solutions on the base of composition from morphotropic phase boundary (1–x)BiScO₃–xPbTiO₃ with x = 0.64, 0.645, 0.65 were prepared from nitrates solutions. Variations in phase content, structure parameters, microstructure, dielectric and piezoelectric properties of dense ceramic samples were studied. The first-order phase transitions were observed at temperatures near 700 K. The influence of the processing conditions on the morphology, temperature of phase transitions, and dielectric parameters was observed. In some ceramics effect of dielectric relaxation was observed at high temperatures. This effect was explained by the contribution from ionic transport due to the oxygen vacancies creation during high temperature sintering.

This paper describes recent device developments with relaxor ferroelectric Pb(Zn_1/3Nb_2/3)O₃–PbTiO₃ (PZN–PT) single crystals carried out at Microfine Materials Technologies Pte. Ltd, Singapore. Promising [011]-poled transverse cuts of PZN–PT single crystals and the results on the effect of electric field and axial compressive stress on the rhombohedral-to-orthorhombic (R–O) phase transformation behavior of such cuts are presented and discussed. The single crystal devices described include a compact low-frequency broadband power-efficient underwater tonpilz projector, high sensitivity shear accelerometers and acoustic vector sensors (AVS). The unique characteristics offered by these PZN–PT single crystal devices are highlighted, which serve as examples of new-generation piezoelectric devices and systems for a wide range of demanding applications.

Our progress in the growth of ternary system Pb(In_1/2Nb_1/2)O₃–Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PIMNT) crystals and reviews on the possible developing trends in the piezoelectric crystals are presented. Large PIMNT crystals with 3 inches in diameter have been grown by using a modified Bridgman method. Meanwhile, Mn-doped PIMNT crystals have also been obtained. PIMNT crystals exhibit Curie temperature T_c ~ 190°C, rhombohedral–tetragonal phase transition temperature T_rt > 100°C and coercive field E_c ~ 5.0–7.0 kV/cm on (001) cuts. Meanwhile, higher piezoelectric constant d₃₂ ~ -1500–2200 pC/N, d₁₅ ~ 4000–6000 pC/N and coercive field E_c ~ 7.0–9.0 kV/cm have been achieved on (110) cuts. The development trends of relaxor-based ferroelectric crystals are suggested to grow novel crystals with high rhombohedral–tetragonal phase transition temperature T_rt > 150 ~ 160°C and/or high coercive field E_c and mechanical quality factor Q_m, to promote growth efficiency of PIMNT crystals and to create new growth methods fitting for the growth of metastable or instable crystals.

Grain size effect on piezoelectric properties and thermal stability of perovskite layer structured (PLS) Sr₂Nb₂O₇ ceramics are investigated. The Sr₂Nb₂O₇ ceramics with different average grain sizes from 1.2$\mu$m to 3.6$\mu$m were prepared in different sintering temperatures by solid state reaction method. The average grain size increases, accompanied by a higher relative density of up to 96%. Pure Sr₂Nb₂O₇ ceramics with larger grain size show a remarkable $d_{33}$ of ($1.7\pm 0.1$)pC/N while still with a very high $T_c$ of ($1340\pm 4{)}^{\circ }$C. The thermal depolarization temperature of samples with large grain sizes reach over 1200^∘C and the thermal stability increased with increasing of grain size. The ferroelectric domains structure was observed by PFM and larger grain is easy to form ferroelectric domain then enhance piezoelectric properties. This study demonstrates enhanced piezoelectric properties can be achieved in pure Sr₂Nb₂O₇ by solid state reaction method and bring great revitalization to the Sr₂Nb₂O₇-based ceramics as a promising high-temperature piezoelectric material.

Potassium–sodium niobate (K,Na)NbO₃/(KNN) lead-free ceramics have drawn vast amount of attention as one of the effective alternatives to lead-based ones. In recent years, the author’s group concentrated their work on KNN-based ceramics. This paper reviews the main obtained results in authors’ laboratory on how to enhance the piezoelectric properties of KNN-based ceramics, including the ions or compounds substitution, the constructing and types of phase boundaries near room temperature, the investigation of other tools (sintering aids, synthesis technique, poling conditions) on properties. All the published papers up to now show the developing higher performance with maintaining high Curie temperature of KNN-based ceramics which has great potential for the future and is the key to success for the field.