Tetragonal (Ba, Ca) (Zr, Ti)O_(3) textured ceramics with enhanced piezoelectric response and superior temperature stability

Lead-free ceramics with both high piezoelectric response and good temperature stability are urgently demanded for electromechanical conversion devices.Unfortunately,owing to coexistence of poly-morphic phases near room temperature(RT),enhanced piezoelectric properties were usually achieved with occurrence of strong temperature dependence in modified BaTiO_(3)(BT)-based ceramics.In this work,we demonstrate that tailoring grain orientations of tetragonal BT-based ceramics can effectively produce substantially enhanced and thermally stabilized piezoelectric response.Both<001>c-and<111>c-oriented tetragonal(Ba_(0.85)Ca_(0.15))(Zr_(0.05)Ti_(0.95))O_(3)(BCZT)ceramics with texture degrees F>90%were synthesized via templated grain growth.Interestingly,the ceramics textured along the<001>c polar axis show much higher microscopic and macroscopic piezoelectric properties than those with nonpolar<111>c texture,indicating an“extender”ferroelectricity nature.Compared with randomly oriented samples,the<001>c-oriented ceramics exhibit simultaneously~1.6 times higher piezoelectric strain d_(33)^(*)(~760 pm/V),4.4 times higher piezoelectric figure of merit d_(33)×g_(33)(8.8×10^(-12) m^(2)/N),and better temperature stability(strain variation≤5%between RT and 110℃).Such thermally stabilized strain response can be mainly attributed to wide temperature range of tetragonal phase and stable domain structure.This work provides a promising route for further developing lead-free piezoceramics with high and temperature-insensitive performance,which can greatly broaden their application areas.

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.

Ultrahigh electrostrain with excellent fatigue resistance in textured Nb^(5+)-doped(Bi_(0.5)Na_(0.5))TiO3-based piezoceramics

(Bi_(0.5)Na_(0.5))TiO_(3)(BNT)-based lead-free piezoceramics exhibit excellent electric field-induced strain(electrostrain)properties,but often suffer from large hysteresis and poor fatigue resistance,which strongly limit their applications.Here,<00l>textured Nb5+-doped 0.8(Bi_(0.5)Na_(0.5))TiO_(3)–0.2(Bi_(0.5)K_(0.5))TiO_(3)(0.8BNT–0.2BKT)ceramics with a high degree of texturing(~80%)were prepared by the reactive template grain growth(RTGG)method using Bi4Ti3O12 as a template.By the combination of donor doping in the B-site and the RTGG method,the electrostrain performance achieves a significant enhancement.A high electrostrain of 0.65%and a piezoelectric coefficient(*33 d)of 1083 pm/V with reduced hysteresis at an electric field of 6 kV/mm are obtained.No electrostrain performance degradation is observed after unipolar electric field loading of 10^(5)cycles,showing excellent fatigue endurance.These results indicate that the texturing BNT-based lead-free piezoceramics by the RTGG method is a useful approach to developing eco-friendly actuators.

Microstructure, domain structure, ferroelectric and piezoelectric properties of textured bismuth-containing ceramics

In this report,the processes of texture formation in grain-oriented ferroelectric ceramics based on layer-structured ferroelectric Bi_(4)Ti_(3)O_(12)(LSBT)prepared by hot forging method are considered.The microstructural and X-ray methods revealed the axial textured formation in ferroelectric ceramic that are used to estimate the orientation factor of ceramics.For the first time,the domain structure changes when poling the anisotropic ferroelectric ceramics are investigated.The anisotropy of electromechanical,piezoelectric and ferroelectric properties of ferroelectric ceramics due to the crystal texture existence in it is studied.The aim of this study is to study the processes of crystalline texture formation in polycrystalline BLSF and to establish the dependence of the electrophysical properties of ceramics on the degree of texturing.Ceramics were textured using the hot stamping(HS)method developed at the Research Institute of Physics.The mechanism of the method is that the workpiece is subjected to uniaxial pressure and free radial deformation occurs due to the plastic flow of the material until the workpiece fills the free volume of the mold,which is created by placing the workpiece in the mold with a gap.The study of the microstructure of ceramics showed that an increase in the firing temperature in the range 950-1050℃ causes a sharp decrease in porosity and increases the density to 7.95 g/cm^(3),which is 98%of theoretical.An X-ray analysis was performed and microstructural studies were carried out,which revealed the formation of an axial texture in ceramics.The features of the switching processes of textured ceramics are revealed.The characteristics of the polarization switching of ceramics in the directions parallel and perpendicular(⊥)of the pressure axis during hot processing were obtained from the dielectric hysteresis P(E)loops,i.e.,axis axial texture.The⊥-cut ceramics are characterized by a more complete polarization switching,which is associated with the additional orientation of the(001)crystallographic planes in the textured material,as well as the presence of a threshold switching field.In the temperature range from-196 to+600℃,the anisotropy of the electro physical properties of ceramics due to the presence of a crystalline texture in it was studied.The dielectric constant,electrical conductivity,piezoelectric and elastic coefficients were measured for sections of ceramics of different orientations relative to the axis of the texture.The anisotropy of the dielectric constant and electrical conductivity manifests itself weakly at room temperature and increases sharply when approaching the Curie temperature.In the temperature range+20-400℃,the high thermal stability of the piezoelectric module d_(33),measured by the quasistatic method,was established.

Si/Al order and texture orientation optimization of red-emitting Mg_(2)Al_(4)Si_(5)O_(18):Eu^(2+)ceramics for laser phosphor display

Laser phosphor display technology plays an important role in advanced display projection;however,it is a challenge in maintaining excellent color accuracy under high brightness due to the lack of red spectrum.Here,red-emitting Mg_(2)Al_(4)Si_(5)O_(18):Eu^(2+)ceramics as the phosphor wheel have been optimized in chemical compositions and texture orientation.The textured Mg_(2)Al_(4)Si_(5)O_(18):Eu^(2+)ceramics have high transparency and spot limiting ability,accordingly,the ceramic wheel outputs 1,184 lm of ultra-bright red light under 50 W/mm^(2) laser power density.Moreover,the red spectral utilization(over 600 nm)of textured Mg_(2)Al_(4)Si_(5)O_(18):Eu^(2+)ceramics is 2.17 times that of traditional Y3Al5O12:Ce^(3+)phosphor wheel.The red-emitting textured Mg_(2)Al_(4)Si_(5)O_(18):Eu^(2+)cordierite ceramic herein enables an improved light-color saturation experience,and it is potential in the next-generation laser phosphor display applications.

Ultrahigh strain in textured BCZT-based lead-free ceramics with CuO sintering agent

Textured BaTiO_(3)(BT)-based lead-free ceramics have gained significant attention due to their high piezoelectric coefficient(d)and very large field induced strain(S).However,costly nano-size raw materials,excessively high sintering temperature and low Curie temperature(T_(c))hinder their device applications.In this work,highly[001]_(c)-oriented(Ba_(0.95)Ca_(0.05))(Zr_(0.04)Ti_(0.96))O_(3) ceramics with x mol%CuO(x=0.25,0.5,1.0,2.5)denoted as BCZT-x were synthesized by templated grain growth using micro-sized raw powders.The introduction of CuO sintering agent lowered the sintering temperature by 125℃ to 1450℃,and the BCZT-1.0 achieved a high texture degree of∼99%.In addition,the CuO-based liquid phases eliminated boundaries between BT templates and BCZT matrix powders.Such liquid-phase sintering reduced sintering stresses,decreased the average grain size of BCZT-1.0 from 16μm down to 13μm,and increased the dielectric dispersion coefficientγto 1.63.The almost smoothed out T_(O-T) anomaly in the temperature dependence of dielectric permittivity and comparably high T_(c)(>102℃)lead to better temperature stability.The narrower grain orientation distribution with full width at half maximum(FWHM)of∼5.9°and smaller domains with the size of 0.1–0.5μm in width and 3–8μm in length were obtained,a high field induced maximum strain S_(max) of 0.38%and low H_(s) of 5.2%have been achieved in BCZT-1.0 textured ceramics together with a high and homogeneous piezoelectric stress coefficient d_(33)∼780 pC/N and very large d_(33)∗∼2950 pm/V.

Large electromechanical strain at high temperatures of novel <001> textured BiFeGaO3-BaTiO3 based ceramics

BiFeGaO3-BaTiO3(BFG-BT)based ceramics with a large piezoelectric coefficient are potential high performance lead-free piezoelectric compounds.In this work,textured and random BFG-BT ceramics were realized by the solid state reaction method with and without BaTiO3(BT)templates.Textured ceramics were obtained by a reactive templated grain growth(RTGG)method leading to a high-temperature electromechanical strain of S=0.27%at 40 kV/cm and to an effective piezoelectric coefficient(d33*)up to 685 pm/V at 180℃.The easy movement of oriented domains enhanced the electromechanical strain under an applied electric field in textured sample(Lotgering factor f=66.3%).Structural investigations reveal that the proportion and degree of distortion of BFG-BT rhombohedral phase(R3c)reached its maximum in textured ceramics,resulting in large ferrodistortive displacements under electric fields.In addition,the dense nanodomains with low domain wall energies,inferred from the high-resolution transmission electron microscope(HR-TEM)observations,contribute to the extra displacement of the textured sample under an applied electric field.In textured ceramics,the remnant polarization was stable(about 17μC/cm2)from room temperature to 180℃,contributing to the stable ferroelectric property at high temperatures.Through the introduction of BT templates,high-density nanodomains were formed and the Burns temperature was enhanced in textured ceramics.The electromechanical strain,polarization and dielectric behavior were correlated to the textured or random forms of the BFG-BT based ceramics.

Temperature-insensitive KNN-based ceramics by elevating O-T phase transition temperature and crystal texture

The inferior temperature stability of piezoelectric response is the main drawback of KNN-based ceramics.Here,the Ba-doped 0.97(K0.48Na0.52)(Nb0.96Sb0.04)O3-0.03Bax(Bi0.5Ag0.5)1-xZrO3(abbreviated as KNNSBxBAZ)textured ceramics were prepared by the template grain growth(TGG)method.Excellent comprehensive properties(d33¼(406±15)pC/N,TC=274℃,strain is 0.17%)were achieved in KNNSBxBAZ textured ceramics with x=0.2.Meanwhile,its piezoelectric and strain properties also show superior temperature stability(d33 maintained within±20%change in awide temperature range from 25℃to 200℃and strain variation was less than 5%in the temperature range from room temperature to 165℃).The high O-T phase transition temperature(TO-T is 110℃)induced by incorporating Ba ions accounts for the enhanced temperature stability of piezoelectric properties.In addition,the crystal texture always maintains the contribution of piezoelectric anisotropy to the piezoelectric properties during elevated temperature,which significantly improved the temperature stability of piezoelectric properties.This work provides an effective strategy for simultaneously achieving high piezoelectric response and excellent temperature stability in KNN-based ceramics.

A design for preparation of textured piezoelectric ceramics based on the phase-field simulation

To solve the problem of directional arrangement of small template particles,we designed a lamination technique for the preparation of dense ceramics with high texture degree based on the phase-field simulation.Referring to the experimental data,the initial microstructures of the template and matrix layers were constructed.The effect of the average length of template on the coarsening behavior of the template layer was investigated in detail.The results suggested that there was a stable stage in the growth process of template grains,which would be conducive to the densification of textured ceramics.This phenomenon has been confirmed by corresponding experiments.In addition,we demonstrated a critical thickness of matrix layer for the preparation of highly textured ceramics by using the template with various average lengths.The grain size of highly textured ceramics could be controlled by adjusting the template size and thickness of matrix layer.

Performance enhancement of ultrasonic transducer made of textured PNN-PZT ceramic

In this paper,0.36Pb(Ni_(1/3)Nb_(2/3))O_(3)-0.24PbZrO3-0.40PbTiO_(3)(PNN-PZT)ceramic was prepared,and texture engineering was performed on this PNN-PZT ceramic to improve its electromechanical properties and temperature stability.Single element ultra-sonic transducers were prepared using PNN-PZT,PNN-PZT textured ceramics,and their performance were evaluated and com-pared using a PZT-5H ceramic based transducer as the benchmark.It is shown that the sensitivity and bandwidth of the PNN-PZT textured ceramic-based transducer are much superior to regular PNN-PZT ceramic and PZT-5H ceramic based transducers.