Dielectric and piezoelectric properties of(Li,Ce) modified NaBi_5Ti_5O_(18) composite ceramics

Nominal （Li0.5Ce0.5）x（Na0.5Bi0.5）（1-x）Na0.5Bi4.5Ti5O18 composite ceramics were fabricated using conventional solid-state reaction method. The coexistence of bismuth layer-structured phase and perovskite phase was determined in these ceramics using XRD technique. At room temperature, the x=0.11 sample showed the largest piezoelectric constant, d33, of about 26.5 pC/N and the largest electromechanical coupling factor, kt, of about 30%. Even after annealing at 500 ℃, the value of d33 was still about 19 pC/N, in x=0.08-0.11 samples. Moreover these composite ceramics showed low temperature coefficients of dielectric constant and high electrical resistivity in the temperature region of 450-550 ℃. These results indicated that （Li, Ce） modified NaBi5Ti5O18 composite ceramics were promising piezoelectric materials for high-temperature applications.

Preparation and Piezoelectric Properties of CuO-added(Ag_(0.75)Li_(0.1)Na_(0.1)K_(0.05_)NbO_3 Lead-free Ceramics

CuO-doped（Ag0.75Li0.1Na0.1K0.05）NbO3（ALNKN-xCuO, x = 0.2mol%） lead-free piezoelectric ceramics were prepared by the solid-state reaction method in air atmosphere. The effects of CuO addition on the phase structure, microstructure, and piezoelectric properties of the ceramics were investigated. The experimental results show that the ALNKN ceramics without doping CuO possess rhombohedral phase along with K2NbrO16- type phase and metallic silver phase. For all of the CuO-doped ALNKN ceramics, a pure perovskite structure with the orthorhombic phase was obtained by enclosing the samples in a corundum tube. A homogeneous microstructure with＇the grain size of about 1 ~tm was formed for the ceramics with 0.5mo1% CuO. The grain size increases with increasing amount of CuO. The temperature dependence of dielectric properties indicates that the ferroelectric phase of the ALNKN-xCuO ceramics becomes less stable with the addition of CuO. The ceramics with x = lm01% exhibit relatively good electrical properties along with a high Curie temperature. These results will provide a helpful guidance to preparing other AN-based ceramics by solid-state reaction method in air atmosphere.

Dielectric and Piezoelectric Properties of 0-3 PZT/PVDF Composite Doped with Polyaniline

Lead zirconate titanate （ PZT ） / polyvinylidene fluoride （PVDF） 0-3 piezoelectric composites doped with polyaniline （PANI） were obtained by hot-press method. The polarization properties of the composites were characterized by XRD and P- E hysteresis loops at room temperature. And the dielectric and piezoelectric properties were also measured. The results show that the poling of PZT could be effectively carried oat and the dielectric constant e, and dissipation tanδ increase monatonously by increasing the volume fraction of PANI in the composite. The piezoelectric constant d33, and the planar electromechanical coupling factor kp increase while the mechanical quality factor Qm decreases with the increase in the content of PANI. The d33, kp and Qm show the extremum values at 8 vol%-10 vol% PANI.

Electronic,Elastic and Piezoelectric Properties of Two-Dimensional Group-Ⅳ Buckled Monolayers

Electronic, elastic and piezoelectric properties of two-dimensional （2D） group-IV buckled monolayers （GeSi, SnSi and SnGe） are studied by first principle calculations. According to our calculations, SnSi and SnGe are good 2D piezoelectric materials with large piezoelectric coefficients. The values of d11d11 of SnSi and SnGe are 5.04pm/V and 5.42pm/V, respectively, which are much larger than 2D MoS2 （3.6pm/V） and are comparable with some frequently used bulk materials （e.g., wurtzite AlN 5.1pm/V）. Charge transfer is calculated by the L wdin analysis and we find that the piezoelectric coefficients （d11d11 and d31） are highly dependent on the polarizabilities of the anions and cations in group-IV monolayers.

Effect of doped Mn on piezoelectric properties of (Na_(0.5)Bi_(0.5))_ (0.92)Ba_(0.08)TiO_3 lead-free ceramics

Piezoelectric ceramics (Na0.5Bi0.5) （0.92）Ba0.08TiO3 +x%MnCO3（BNBT-Mn, x=0CD*21.6, mass fraction） were synthesized by conventional solid state reaction. The results show that when the addition of MnCO3 is 0CD*2 1.4%, BNBT-Mn ceramics exhibit a single-phase perovskite structure. With the increase of content of MnCO3, piezoelectric constant and electromechanical coupling factor increase rapidly when x is lower than 0.3. Then they both decrease when x is in the range of 0.3 and 1.6. When x=0.3, piezoelectric constant and electromechanical coupling factor reach the maximum value of 160pC/N and 58.5% respectively, which can improve the temperature stability of BNBT-Mn.

Enhanced piezoelectric properties of Nd^(3+) doped nano-lead zirconate titanate piezoelectric ceramics

Nd3+ doped lead zirconate titanate (Pb1-3x/2NdxZr0.52Ti0.48O3, PNZT) nanopowders were prepared through a modified sol-gel method. The effects of Nd3+ doping on the microstructures and properties of PNZT ceramics have been studies. The grain sizes of the perovskite PNZT nanopowders were about 100nm and the lattice distortion of the PNZT increased with the content of Nd3+ up to 9 mol%. The dopant of Nd3+ resulted in the decrease of crystal lattice parameter a and the obvious increase of c and c/a, which effectively improved the sintered densification and activity of the PNZT ceramics. Due to lead vacancies caused by the doping of Nd3+ in the PZT, the piezoelectric constant, electromechanical coupling coefficient and dielectric constant observed were much higher than the monolithic PZT.

Piezoelectric properties of low loss and high Curie temperature (Bi, La)FeO_3-Pb(Ti, Mn)O_3 ceramics with Mn doping

Piezoelectric ceramics of 0.6(Bi0.9La0.1)FeO3-0.4Pb(Ti1-xMnx)O3 (BLF-PTM) for x=0, 0.01, 0.02, and 0.03 were prepared by sol-gel process combined with a solid-state reaction method. The tan? for BLF-PTM of x=0.01 is just 0.006 at 1 kHz, drastically decreasing by using Mn dopants. The TC increases to 490 ℃ for BLF-PTM of x=0.02. Furthermore, Mn modification effectively enhances the poling state and the piezoelectric properties of BLF-PTM. The kp, Qm, d33, and g33 of 0.34, 403, and 124 pC1·N-1 and 37×10-3 Vm·N-1 are achieved for BLF-PTM of x=0.01. The results indicate that Mn modified BLF-PTM is a competitive high power and high temperature piezoelectric material with excellent piezoelectric properties.

Dielectric and piezoelectric properties of(110) oriented Pb(Zr_(1-x)Ti_x)O_3 thin films

A phenomenological Landau–Devonshire theory is developed to investigate the ferroelectric, dielectric, and piezoelectric properties of（110） oriented Pb（Zr_（1-x）Ti_x）O_3（x = 0.4, 0.5, 0.6, and 0.7） thin films. At room temperature, the tetragonal a_1 phase, the orthorhombic a_2c phase, the triclinic γ_1 phase, and the triclinic γ_2 phase are stable. The appearance of the negative polarization component P_2 in the a_2c phase and the γ_1 phase is attributed to the nonlinear coupling terms in the thermodynamic potential. The γ phase of the Pb（Zr_（1-x）Ti_x）O_3 thin films has better dielectric and piezoelectric properties than the a_2c phase and the a_1 phase. The largest dielectric and piezoelectric coefficients are obtained in the Pb（Zr_（0.5）Ti_（0.5））O_3 thin film. The piezoelectric coefficient of 110–150 pm/V is obtained in the（110） oriented Pb（Zr_（0.5）Ti_（0.5））O_3 thin film, and the Pb（Zr_（0.3）Ti_（0.7））O_3 thin film has the remnant polarization and relative dielectric constant of 50 μC/cm^2 and 100, respectively,which are in agreement with the experimental measurements reported in the literature.

Convenient folding-hot-pressing fabrication and enhanced piezoelectric properties of highβ-phasecontent poly(vinylidene fluoride)films

Poly(vinylidene fluoride)(PVDF)is the most attractive piezoelectric polymer for application in flexible sensors.To attain excellent piezoelectric properties,a substantial amount of spontaneous polarβ-phase content is highly desired.Nevertheless,the current reported manufacturing methods to increaseβ-phase contents are inconvenient and complex,hindering progress in PVDF's application.This work proposes a folding-hot-pressing method to fabricate highβ-phase-content PVDF films.Structural characterization indicates that the films haveαandβphases and the folding-hot-pressing process transforms theαphase into theβphase.Due to the 97.5%β-phase content and aligned structure,a piezoelectric constant of 20 pC/N is achieved in the three-times folded film.Furthermore,the process method enhances the tensile strength(126.2 MPa)of the films,with a low Young's modulus(0.87 GPa)remaining,making the films applicable for flexible piezoelectric sensors.Additionally,sensors based on the achieved films were assembled and applied for human physiological activity monitoring.This work offers a scalable new melt-processing strategy for developing high-performance PVDF-based piezo-electric composite films for wearable electronic devices.

Enhanced piezoelectric properties and thermal stability of LiNbO_(3)-modified PNN-PZT ceramics

Piezoelectric PZT ceramics with high piezoelectric properties and good thermal stability are urgently desired concerning the practical application.New compositions of LiNbO_(3) modified Pb(Ni_(1/3)Nb_(2/3))O_(3)single bondPbZrO_(3)single bondPbTiO_(3) ceramics have been prepared in this study.The effects of the introduction of the LiNbO_(3) on the system were comprehensively investigated in terms of the phase structure,microstructure,electric properties,and thermal stability behavior of the ceramics.All compositions are located in the morphotropic phase boundary(MPB)region,and the ratio of the rhombohedral(R)phase increases obviously with the increase of LiNbO_(3) concentration.With increasing the LiNbO_(3) content,the piezoelectric properties were significantly enhanced.The sample added with 2%(in mole)LiNbO_(3) shows excellent electric properties,including T_(m)=185℃,εr=5,643,k_(p)=0.626,Q_(m)=51,d_(33)=902 pC/N.More importantly,no thermal depolarization behavior was observed in the temperature range of 25–100℃.For PNN-PZT-x%LN ceramics,which is mainly attributed to the pinning effect resulted by the(Li_(Pb)-Nb_(Zr/Ti)) defect dipoles.

Enhanced piezoelectric properties and electrical resistivity in CaHfO_(3)modified BiFeO_(3)eBaTiO_(3)lead-free piezoceramics

A number of CaHfO_(3)modified BiFeO_(3)-0.33BaTiO_(3)(BF-0.33BT-xCH)lead-free piezoceramics were fabri-cated through the solid-state sintering method and comprehensively investigated in this work.Under the optimal sintering temperature,all compositions display a typical perovskite structure in a pseudo-cubic phase with slightly larger lattice parameters as the CH content increases.The electrical resistivity is highly enhanced due to the addition of CH.Microstructures,including the grain morphology,core-shell structure,and chemistry inhomogeneities,are demonstrated upon different BF-0.33BT-xCH composi-tions.In particular,the core-shell structures with non-uniform element distributions in the compositions can be eliminated by adding sufficient CH content(x>0.05).The highest saturation polarization(40.1 mC/cm^(2)),remnant polarization(26.8 mC/cm^(2)),and converse piezoelectric coefficient(290 pm/V)are achieved in the BF-0.33BT-0.01CH piezoceramic,which are significantly enhanced in comparison with the undoped BF-0.33BT piezoceramic.With further increasing the CH content,the piezoelectric properties of BF-0.33BT-xCH ceramics decline rapidly,and they start to exhibit characteristics of relaxor ferroelectrics.

Effects of Cr_2O_3 doping on the electrical properties and the temperature stabilities of PZT binary piezoelectric ceramics

The ceramics with Pb1.04Zr0.52Ti0.48O3 ＋ z wt.% Cr2O3 were prepared using the traditional technique. The effects of Cr2O3 doping on the phase structure, the microstructure, and the electrical properties of ceramics were investigated. Meanwhile, the temperature stabilities of the resonant frequency （fx） were studied. The results showed that the △fr/fr,25℃ decreased with the addition of 0.2 wt.% - 0.8 wt.% Cr2O3 as compared with the undoped samples. The minimum value （-0.182%） of △fr/fr,25℃ was obtained for z = 0.6 wt.% Cr2O3 samples that sintered at 1260℃. The values of ε^τ33/ε0 = 1650, tanδ = 0.006, d33 = 328 pC/N, Kp = 0.63, Qm = 2300 were obtained when Cr2O3 was 0.6 wt.%, which exhibited more excellent piezoelectric properties than other compositions such as those with z = 0.2 wt.%, 0.4 wt.%, and 0.8 wt.%, but had a similar value as compared with the tmdoped samples. When the Cr2O3 additive increased, the Curie temperature moved toward low temperature and the changes of resonant frequency changed from positive to negative with increasing temperature.

Enhanced piezoelectric properties in low-temperature sintering PZN-PZT ceramics by adjusting Zr/Ti ratio

Pb_(0.96)Sr_(0.04)(Zr,Ti)_(0.7)(Zn_(1/3)Nb_(2/3))_(0.3)O_(3)(PZN-PZT)piezoceramics with various Zr/Ti ratios and Li_(2)CO_(3)sintering aid were sintered at 900°C by the solid-state reaction route.The samples with different Zr/Ti ratios were compared according to microstructure,phase structure,piezoelectricity,ferroelectricity,and dielectric relaxation.The Zr/Ti ratio in the PZN-PZT ceramics greatly affects the electrical properties.The Zr/Ti ratio affects the proportion between the rhombohedral and tetragonal phases and also affects the grain size.The PZN-PZT ceramics with the Zr/Ti ratio of 53:47 have the largest grain size and have optimized piezoelectric prop-erties(k_(p)=0.58,d_(33)=540 pC/N,and T_(C)=250°C).The larger the grain size,the lesser the grain boundary,the easier the domain wall motion,and the better the piezoelectric properties.The PZT ceramic with Zr/Ti ratio of 53:47 locates the morphotropic phase boundary(MPB)region which is one of the key factors for the high piezoelectric properties of the PZT.

Effect of Li content on the microstructure and properties of lead-free piezoelectric(K_(0.5)Na_(0.5))_(1-x)Li_xNbO_3 ceramics prepared by SPS

Lead-free piezoelectric （K0.5sNa0.5）1-xLixNbO3 （x = 0at%-20at%） ceramics were synthesized by spark plasma sintering （SPS） at low temperature and the effects of LiNbO3 addition on its crystal structure and properties were also studied. When the Li content was less than 6at%, a single proveskite phase with the similar structure of （K0.5Na0.5）NbO3 was formed; and a secondary phase with K3Li2Nb5O15 structure was observed in the 6at% 〈 x 〈 20at% compositional range. Furthermore, LiNbO3 existed as the third phase when the Li content was higher than 8at%. The grain sizes increased from 200-500 nm to 5-8 μm when the K3Li2Nb5O15 and LiNbO3 like phases were formed. With increasing Li content, the relative density of the ceramics first decreased from 97% to 93% and then kept constant. The piezoelectric coefficient d33, dielectric constant, and planner electromechanical coupling factor exhibited a decreasing tendency with increasing Li content because of the decrease in density and the formation of the secondary phase such as K3Li2Nb5O15 and LiNbO3. The formation of dense microstructure with a single phase is necessary in improving the properties of the （K0.5Na0.5）1-xLixNbO3 ceramics.

Enhanced piezoelectric properties and temperature stability in KNN-based textured ceramics

Considering the advantages of high Curie temperature and environment-friendly nature of KNN piezoelectric ceramics,the limitation of weak piezoelectric response and their temperature sensitivity to applications is worth exploring.Herein,the<001>textured(1-x)(K_(0.5)Na_(0.5))(Nb0.96Sb0.04)O3-x(Bi_(0.5)Na_(0.5))HfO_(3)(x=0.01-0.045)lead-free ceramics were synthesized by templated grain-growth method.The high piezoelectric performance(d33 of 474 pC/N and strain of 0.21%)and excellent temperature stability(unipolar strain maintained within 4.3%change between 30℃and 165℃)were simultaneously achieved in the textured KNNS-0.03BNH ceramics.The high piezoelectric performance can be attributed to the summation of the crystallographic anisotropy and phase structure contributions in<001>textured ceramics.The superior temperature stability of piezoelectric properties can be interpreted by the contribution of crystal anisotropy to piezoelectric properties reduces the effect of phase transition on piezoelectric properties deterioration.This study provides an effective strategy for simultaneously achieving high piezoelectric properties and superior temperature stability in KNN-based textured ceramics.

Modified phase transition and electrical properties of [Li_(0.05)(Na_(0.535)K_(0.48))_(0.95)]- (Nb_(0.94)Sb_(0.06))O_3 lead-free piezoelectric ceramic by sintering temperature

Li/Sb-doped (Na,K)NbO3 with a nominal composition of [Li0.05(Na0.535K0.48)0.95](Nb0.94Sb0.06)O3 ceramic was synthesized by normal sintering. The phase structure, microstructure, and electrical properties were investigated with a special emphasis on the influence of the sintering temperature. A polymorphic phase transition (PPT) from orthorhombic to tetragonal symmetry was observed when the sintering temperature was raised from 1040 to 1050 ℃, whereby the piezoelectric coefficient d33 and the electromechanical coupling coefficient kp reached the peak values of 245 pC·N-1 and 41.2%, respectively. The PPT induced by varying the sintering temperature is due to the different volatilization extents of alkali metals and appears to a lower sintering temperature with increasing Li content. The trace modifying of alkali metal content is more effective than doping B site element to enhance the d33 value.

Piezoelectric and dielectric properties of Cr-doped PSN-PZN-PZT qua-ternary piezoelectric ceramics

PSN-PZN-PZT + x wt. %Cr2O3, X = 0.0-0-9, were prepared by conventional mixed oxide techniques at sintering temperatures of 1220 degrees C-1300 degrees C for 2 h. The effect of sintering temperature on the microstructure and the piezoelectric properties was investigated by XRD, SEM, and other conventional measurement. The result indicated that with temperature increasing, the valence of Cr ion from Cr5+ or Cr6+ changes into C3+, and the piezoelectric properties turn hard. With increasing Cr2O3 content, the amount of rhombohedral phases increases and the morphotropic boundary phase is correspondingly shifts to rhombohedral phase. A uniform microstructure and excellent comprehensive properties were obtained at 1240 degrees C as the amount of Cr2O3 is 0.5 wt.%.

Improved ferroelectric and piezoelectric properties of(Na_(0.5)K_(0.5))NbO_(3)ceramics via sintering in low oxygen partial pressure atmosphere and adding LiF

Dense(Na_(0.5)K_(0.5))NbO_(3)lead-free ceramics with the simple composition were prepared via sintering in low oxygen partial pressure(pO_(2),~10^(−12) atm)atmosphere and adding LiF.All the ceramics have pure orthorhombic structure.Compared to the LiF-added(Na_(0.5)K_(0.5))NbO_(3)ceramics sintered in air and the low pO_(2)-sintered pure(Na_(0.5)K_(0.5))NbO_(3)ceramics without LiF addition,the present ceramics exhibit improved piezoelectric and ferroelectric properties.The piezoelectric constant d33 is 125 pC/N,and the converse piezoelectric constant d_(33)^(*)is 186 pm/V.The dielectric constant and dielectric loss of the ceramics at room temperature and 1 kHz are 451 and 0.03,respectively.Under the measured electric field of 70 kV/cm,the remanent polarization is 25.9μC/cm^(2)and the coercive field is 13.9 kV/cm.Furthermore,if the base metals such as Cu and Ni powders were mixed into the green pellets and sintered in the low pO_(2)atmosphere,the base metals cannot be oxidized,suggesting possibility of using base metals as electrodes.

Effects of Excess Barium on the Structure and Electrical Properties of(Ba,Ca)TiO_3 Piezoelectric Ceramics with High Mechanical Quality Factors

Manganese-doped Ba（0.925）Ca（0.075）TiO3 lead-free piezoelectric ceramics（abbreviated as BCT）with high mechanical quality factor were synthesized by conventional solid-state reaction method.The effects of excess Ba on the crystal structure,microstructure,and electrical properties of the ceramics were systematically investigated.X-ray diffraction and Raman spectra revealed that Ca^2＋ions were pushed from Ba sites to Ti sites of BCT when 1.5 mol%extra Ba^2＋ions were added after sintering.The grain size of the ceramics was decreased by adding extra Ba^2＋ions.The mechanical quality factor and resistivity of the ceramics decreased dramatically when the excess Ba was more than 1.5 mol%.High piezoelectric coefficients（d（33）=150-190 pC/N）and high mechanical quality factors（Qm=1 000-1 200）were obtained in the ceramics when the excess of Ba was between 0.5 mol%and 1 mol%.These results indicated that the properties of BCT ceramics could be tailored by adjusting the content of Ba.

Structure,microstructure,dielectric and piezoelectric properties of(1−x-y)BiFeO_(3)-xPbFe_(0.5)Nb_(0.5)O_(3)-yPbTiO_(3)ceramics

Ceramics of quasi-binary concentration section(x=0.50,0.1≤y≤0.2,Δy=0.025)of the ternary solid solution system(1−x−y)BiFeO_(3)-xPbFe_(0.5)Nb_(0.5)O_(3)-yPbTiO_(3)were prepared by the conventional solid-phase reaction method.By using X-ray diffraction technique,the phase diagram of the system was constructed,which was shown to contain the regions of cubic and tetragonal symmetry and the morphotropic phase boundary between them.Grain morphology,dielectric and piezoelectric proper­ties of the selected solid solutions were investigated.The highest piezoelectric coefficient d_(33)=260 pC/N was obtained.Dielectric characteristics of ceramics revealed ferroelectric relaxor behavior,a region of diffuse phase transition from the paraelectric to ferroelectric phase in the temperature range of 350-500 K.