(Ba0.85Ca0.15)(Ti0.90Zr0.06Sn0.04)O3-Fe2O3无铅压电陶瓷的性能研究

采用固相法制备了(Ba0.85Ca0.15) (Ti0.90Zr0.06Sn0.04)O3-xmol％Fe2O3(简写为BCTZS-xFe)无铅压电陶瓷.研究了不同掺杂量对该陶瓷的显微结构、介电、铁电及压电性能的影响.结果表明,所有样品均具有单一的钙钛矿结构,少量掺杂能使晶粒长大,提高电性能.在x=0.025时,具有最佳的综合电性能,压电常数d33 =515 pC/N,机电耦合系数kp=48.2％,机械品质因数Qm =182,2Pr=18.2 μC/cm2,2Ec =4.3 kV/cm,介电常数εr=5175.     

Enhancing piezoelectric properties of Ba0.88Ca0.12Zr0.12Ti0.88O3 lead-free ceramics by doping Co ions

The piezoelectric properties of lead-free Ba_0.88Ca_0.12Zr_0.12Ti_0.88O₃ (BCZT) ceramics were greatly optimized by doping Co ions using a CoO powder. The role of Co²⁺ and Co³⁺ in enhancing the piezoelectric properties and the relationship between the content ratio Co³⁺/Co²⁺ and piezoelectric performance were studied. The X-ray diffraction patterns of all samples indicated that crystalline phases were a BCZT-based single perovskite structure regardless of the Co ion content. The phase transition temperature and lattice distortion degree were related to the Co ion content and the content ratio Co³⁺/Co²⁺ because Co²⁺ resulted in higher oxygen vacancy generation, whereas Co³⁺ induced larger lattice shrinkage. The ceramic containing 0.10 wt% of Co ion showed the best piezoelectric and dielectric performance with the highest piezoelectric constant d₃₃ ~ 490 p.m./V at room temperature and the highest Curie temperature T_c of 110 °C, which increased by 29% and 16%, respectively. In this case, the content ratio Co³⁺/Co²⁺ reached the maximum value of 0.86. The high piezoelectric properties and phase stability of BCZT ceramics by doping Co ions make these ceramics promising piezoelectric materials for practical applications.     

The effects of sintering atmospheres on piezoelectric performances of Co-doped Ba0.88Ca0.12Zr0.12Ti0.88O3 ceramics

This work investigates the effects of content ratio Co³⁺/Co²⁺ on piezoelectric properties of lead-free Ba_0.88Ca_0.12Zr_0.12Ti_0.88O₃ (BCZT) ceramics. For this purpose, 0.10 wt% Co ions using a CoO powder doped BCZT ceramics were sintered under various atmospheres (ranging from pure nitrogen to 100 vol% oxygen concentration) to vary the ratio value Co³⁺/Co²⁺. X-ray photoelectron spectroscopy analysis revealed the coexistence of Co³⁺ and Co²⁺ for oxygen concentration below 40 vol% and the single oxidation state of Co³⁺ for oxygen concentration over 50 vol%. Co²⁺ substitution could induce more oxygen vacancy to accelerate densification and grain growth, whereas Co³⁺ substitution usually leads to larger lattice distortion to generate a stable asymmetric structure. When oxygen concentration was 30 vol% and Co³⁺/Co²⁺ near to 1.0, the respective superiority of Co³⁺ and Co²⁺ is brought into full play, and the ceramic showed the highest piezoelectric constant d₃₃^* ∼ 518 pm/V (380 pm/V for undoped BCZT) and the relatively high Curie temperature T_c ∼ 105°C (95°C for undoped BCZT). This study suggests that optimizing sintering atmosphere might be an effective way to enhance the piezoelectric properties for some composition-modified piezoelectric BCZT ceramics.     

High‐Energy Storage Performance of (Pb0.87Ba0.1La0.02)(Zr0.68Sn0.24Ti0.08)O3 Antiferroelectric Ceramics Fabricated by the Hot‐Press Sintering Method

(Pb_0.87Ba_0.1La_0.02)(Zr_0.68Sn_0.24Ti_0.08)O₃ (PBLZST) antiferroelectric (AFE) ceramics have been prepared by hot‐press sintering method and conventional solid‐state reaction process, and the dependence of microstructure and energy storage properties of the ceramics on sintering approaches has been studied. The results reveal that not only the microstructure, but also the electrical properties of the PBLZST AFE ceramics are significantly improved by using the hot‐press sintering method. Samples resulting from the hot‐press sintering process have high breakdown strength of 180 kV/cm which results from the increase of density. Coupled with large polarization, the hot‐pressed AFE ceramics are shown to have a high recoverable energy density of 3.2 J/cm³. The recoverable energy density of the hot‐pressed PBLZST AFE ceramics is 100% greater than the conventional sintered specimens with recoverable energy density of 1.6 J/cm³.     

Effect of Ba Content on the Stress Sensitivity of the Antiferroelectric to Ferroelectric Phase Transition in (Pb,La,Ba,)(Zr,Sn,Ti)O3 Ceramics

The effect of Ba content on the stress sensitivity of the antiferroelectric to ferroelectric phase transition in (Pb_0.94?xLa_0.04Ba_x)[(Zr_0.60Sn_0.40)_0.84Ti_0.16]O₃ ceramics is investigated through monitoring electric field‐induced polarization and longitudinal strain under compressive prestresses. It is found that incorporation of Ba significantly suppresses the stress sensitivity of the phase transition, as manifested by slight decreases under prestresses up to 100 MPa in the maximum polarization (P_m) and longitudinal strain (x_m). The energy storage density is even increased under the mechanical confinement in compositions x = 0.02 and 0.04. X‐ray diffraction, transmission electron microscopy, and dielectric measurements indicate that the suppressed stress sensitivity is associated with the disruption of micrometersized antiferroelectric domains into nanodomains and the transition from antiferroelectric to relaxor behavior.     

Ba(Zr0.3Ti0.7)O3薄膜的结构及性能

用溶胶-凝胶法分别在Pt/Ti/SiO2/Si和LaNiO3/Pt/Ti/SiO2/Si衬底上制备了锆钛酸钡[Ba(Zr0.3Ti0.7)O3,BZT]薄膜.相结构及介电性能研究表明:衬底和薄膜厚度对BZT薄膜性能具有显著影响.制备在LaNiO3/Pt/Ti/SiO2/Si衬底上的BZT薄膜具有(100)面的择优取向,其介电常数及介电损耗则随着薄膜厚度的增加而降低.对制备在Pt/Ti/SiO2/Si衬底上的BZT薄膜,在薄膜厚度低于500nm时,其介电常数随薄膜厚度增加而增加,大于500nm时又有所减小.     

(Pb,Sm)(Zr,Sn,Ti)O3 Multifunctional Ceramics with Large Electric‐Field‐Induced Strain and High‐Energy Storage Density

Recently, the progress of integrated electronics has led to a strong demand for materials and devices with multiple functions. In this study, we achieved Pb_0.985Sm_0.01 (Zr_0.64Sn_0.28Ti_0.08)O₃ (PSZST) multifunctional ceramics which showed simultaneously large electric‐field‐induced strain (0.63%) and high recoverable energy density (1.743 J/cm³) at room temperature. Moreover, the strain and recoverable energy density exhibited a slight frequency fluctuation in the frequency range of 1–10 Hz. Their variations were less than 8% and 1.3% and the values were all higher than 0.58% and 1.722 J/cm³, respectively. The large strain, high‐energy density, and their good frequency stability in a wide range indicate that the PSZST ceramic is quite promising for application in multifunctional devices.     

Ca0.7Ti0.7La0.3Al0.3O3微波介质陶瓷微观组织结构与介电性能

采用固相反应法制备斜方晶系钙钛矿结构Ca07Ti07La0.3Al0.3O3微波介质陶瓷,研究了Al3+、Ca2、Ba2+和La3+离子掺杂对CTLA陶瓷微观组织结构和介电性能的影响.研究结果表明不同掺杂离子对于CTLA陶瓷的微观结构和介电性能有很大的影响,不同离子掺杂CTLA陶瓷的晶粒尺寸、气孔率、晶界析出相有很大的不同.Al3+、Ca2+、Ba2+和La3+离子掺杂可以有效降低CTLA陶瓷的谐振频率温度系数,但Ca2+、Ba2+离子掺杂同时也降低了CTLA陶瓷的致密度和Q×f值,Al3+、La3+离子掺杂不仅有效提高了CTLA陶瓷的致密度和Q×f值,并且有效降低了谐振频率温度系数.适量掺杂La3离子可以有效促进CTLA陶瓷的致密化,提高了CTLA陶瓷的微波介电性能.掺杂0.15mol％ La3+的CTLA陶瓷在4.7 GHz下测试介电性能为:εr=48.39,Q×f=32560 GHz,τf=23.68 ppm/C.     

Domain wall-grain boundary interactions in polycrystalline Pb(Zr0.7Ti0.3)O3 piezoceramics

Interactions between grain boundaries and domain walls were extensively studied in ferroelectric films and bicrystals. This knowledge, however, has not been transferred to polycrystalline ceramics, in which the grain size represents a powerful tool to tailor the electromechanical and dielectric response. Here, we relate changes in dielectric and electromechanical properties of a bulk polycrystalline Pb(Zr_0.7Ti_0.3)O₃ to domain wall interactions with grain boundaries. Samples with grain sizes in the range of 3.9–10.4 μm were prepared and their microstructure, crystal structure, and dielectric/electromechanical properties were investigated. A decreasing grain size was accompanied by a reduction in large-signal electromechanical properties and an increase in small-signal relative permittivity. High-energy diffraction analysis revealed increasing microstrains upon decreasing the grain size, while piezoresponse force microscopy indicated an increased local coercive voltage near grain boundaries. The changes in properties were thus related to strained material volume close to the grain boundaries exhibiting reduced domain wall dynamics.     

Temperature dependence of ferroelectric property and leakage mechanism in Mn-doped Pb(Zr0.3Ti0.7)O3 films

High-quality ferroelectric films of Mn-doped Pb(Zr_0.3Ti_0.7)O₃ (PMZT) were prepared using the sol-gel method, and the temperature dependence of ferroelectric, dielectric, and leakage current properties (J–E) were explored in detail using the top electrode/ferroelectric films/bottom electrode capacitor heterostructure. The enhancement of polarization and dielectric properties by element doping is clearly observed by 3% Mn-doping. Such enhancement is beneficial for the application of these films in ferroelectric random-access memory. In addition, the analysis of leakage current reveals symmetric behavior with 3% Mn-doping and the leakage current density gradually increases with increasing temperature, which may be due to the movement of domain wall and oxygen vacancy. The dominant leakage current conduction mechanism is bulk-limited ohmic or interface-limited Schottky emission conduction within a wide temperature range. The results might be meaningful for further work on ferroelectric electrical devices with improved ferroelectric and dielectric properties.     

Giant Thermal–Electrical Energy Harvesting Effect of Pb0.97La0.02(Zr0.75Sn0.18Ti0.07)O3 Antiferroelectric Thick Film

In this letter, 2‐μm Pb_0.97La_0.02(Zr_0.75Sn_0.18Ti_0.07)O₃ antiferroelectric thick film with tetragonal structure was prepared. The effects of operating electric field, temperature, and frequency on the thermal–electrical energy harvesting capacity of the film were studied by using the Olsen cycle. The results demonstrated that giant energy harvesting effect could be realized in the antiferroelectric thick film. The maximum harvestable energy density per cycle of the film was about 7.8 J/cm³ at 1 kHz, which was the largest reported value to date. The corresponding energy harvesting efficiency was 0.53%. Moreover, the film had a low leakage current density (about 7.3 × 10^?7 and 3.9 × 10^?5 A/cm² at 25 and 200°C, respectively), which was favorable for its application in the devices of the thermal–electrical energy harvesting.     

Electric fatigue in antiferroelectric Pb0.97La0.02(Zr0.55Sn0.33Ti0.12)O3 ceramics induced by bipolar cycling

Antiferroelectric lead zirconate titanate stannate (PZST) ceramics are promising materials for high-strain transducers and actuators. The degradation of the strain excited by an ac field remains largely unknown so far for this family of antiferroelectric ceramics. In this study, the bipolar electric fatigue of antiferroelectric Pb_0.97La_0.02(Zr_0.55Sn_0.33Ti_0.12)O₃ ceramics was investigated. Variations in the strain hysteresis loop and damage in the microstructure of the materials due to the electric cycling were monitored. Higher cycling field yielded a stronger fatigue effect. The material showed an increasingly asymmetric suppression of the strain hysteresis loop and diffuse AFE–FE phase transition with increasing cycle number. A damaged microstructure was observed on the polished surfaces of fatigued samples after acid etching. Electrochemical variations, the pinning of domains, randomly or preferentially orientated, due to the cycling are considered as the main fatigue mechanism of the material.     

激励方式对锆钛酸铅钡锶压电陶瓷介电性能的影响

采用扎膜工艺和固相反应法制备了(Pb0.70Ba0.26Sr0.04)(Zr0.52Ti0.48)O3(PBSZT)压电陶瓷。通过扫描电子显微镜和X射线衍射表征PBSZT陶瓷的结构和物相组成,用电容介损测试仪表征压电陶瓷的介电性能与激励场强,通过自建电路集成直流电源、标准电容,在低频频率特性测试仪上得到偏场强度对压电陶瓷介电性能的影响关系。结果表明:压电陶瓷材料的介电性能随着加载的电场强度的增大先逐渐升高,而后出现拐点开始降低;在偏压电场中,自由电容CT随正向偏场强度的增加逐渐减小,但随着反向偏场强度的增加逐渐增大。tanδ则随着正、反偏场强度的增加均呈现上升;压电陶瓷的机电耦合系数kp与偏场强度的关系是以0点为界,随着负偏场增强,kp略显下降,反之,随正偏场增强,kp缓慢增大。因此,压电陶瓷应用时应避开强场损耗高点;并在环境中施加正向偏场,有助于抑制压电陶瓷性能衰减。     

Field induced metastable ferroelectric phase in Pb0.97La0.03(Zr0.90Ti0.10)0.9925O3 ceramics

Pb_0.97La_0.03(Zr_0.9Ti_0.1)_0.9925O₃ (PLZT 3/90/10) ceramics prepared by solid-state reaction with the compositions near the antiferroelectric/ferroelectric (FE/AFE) phase boundary were studied. From the polarization–electric field P(E) dependence and ex situ X-ray study, an irreversible electric field induced AFE-to-FE phase transition is verified at room temperature. Dielectric and in situ temperature dependent X-ray analysis evidence that the phase transition sequence in PLZT 3/90/10-based ceramics can be readily altered by poling. A first order antiferroelectric-paraelectric (AFE-to-PE) transition occurred at?～190 °C in virgin sample and at?～180 °C in poled sample. In addition, a FE-to-AFE transition occurs in the poled ceramic at much lower temperatures (～120 °C) with respect to the Curie range (～190 °C). The temperature-induced FE-to-AFE transition is diffuse and takes place in a broad temperature range of 72–135 °C. The recovery of AFE is accompanied by an enhancement in the piezoelectric properties.     

Energy storage and release properties of Sr-doped (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric ceramics

Pb_0.94−xLa_0.04Sr_x[(Zr_0.6Sn_0.4)_0.84Ti_0.16]O₃ (x=0,0.02,0.04,0.06) antiferroelectric ceramics were fabricated via conventional solid-state reaction. The increase of Sr content enhanced the stability of antiferroelectric phase, which resulted in the rise of phase transition fields and energy density. When x=0.06, the releasable energy density was 1.52 J/cm³ and the efficiency was 93.3% under 129 kV/cm. The pulsed discharge current was also measured to evaluate the energy release properties. Under 129 kV/cm, the obtained current density could be as high as 165.5 A/cm². The pulsed discharge energy density was 1.21 J/cm³ and 90% of that could be released in less than 200 ns. The high energy density, high efficiency and fast energy release time indicate that the obtained AFE ceramics are very promising for pulsed power capacitors.     

Phenomenological modeling of phase transitions and electrocaloric effect in Ba(Zr0.2Ti0.8)O3-(Ba0.7Ca0.3)TiO3

Ba(Zr_0.2Ti_0.8)O₃-x(Ba_0.7Ca_0.3)TiO₃ (BZT-xBCT) is a promising lead-free ferroelectric system. In this paper, we present two sets of free energy coefficients and carry out phenomenological modeling to study the phase transition and electrocaloric effect. The calculated phase diagram is in excellent quantitative agreement with experiments. Furthermore, we propose a new method based on effective internal electric field to simulate polarization in the macroscopic paraelectric state of ferroelectric relaxor. The computed composition and temperature-dependent entropy and temperature change induced by electrocaloric effect are in good agreement with the measured data available for single crystal.     

Nano-embossing technology on ferroelectric thin film Pb(Zr0.3,Ti0.7)O3 for multi-bit storage application

In this work, we apply nano-embossing technique to form a stagger structure in ferroelectric lead zirconate titanate [Pb(Zr0.3, Ti0.7)O3 (PZT)] films and investigate the ferroelectric and electrical characterizations of the embossed and un-embossed regions, respectively, of the same films by using piezoresponse force microscopy (PFM) and Radiant Technologies Precision Material Analyzer. Attributed to the different layer thickness of the patterned ferroelectric thin film, two distinctive coercive voltages have been obtained, thereby, allowing for a single ferroelectric memory cell to contain more than one bit of data.     

Hierarchical domain structures in (Pb,La)(Zr,Sn, Ti)O3 antiferroelectric ceramics

(Pb, La)(Zr, Sn, Ti)O₃ (PLZST) ceramic is one of the most prospective antiferroelectric (AFE) materials for variety of functional applications including energy storage and converter. Systematic structural investigation of domain structures should be of fundamental importance for understanding the structure-property relationship in AFE ceramics. In this study, the hierarchical domain structures and modulated structures correlated to the compositional variation in (Pb_0.97La_0.02) (Zr_0.50Sn_xTi_0.50-x)O₃ (x = 0.375, 0.45 and 0.50) were observed and investigated in details by transmission electron microscopy. The PLZST ceramics show exclusively incommensurate modulated structures (IMS) whose modulation period changed from 9.37 to 6.15 and to 4.04 with increasing of the x value. The hierarchical domain structures include, in decreasing scales, AFE domains, incommensurate domains and nanodomains. The elementary domains in PLZST ceramics are pinstriped nanodomains which were formed based on IMS configuration but by frequent modulation of IMS periodicity and formation of faults. Nanodomains accumulated and then dissociated into incommensurate domains and AFE domains successively. The presently revealed structural characteristics in antiferroelectric PLZST may stimulate future researches on the evolution of IMS-based hierarchical domains under external physical fields, e.g. thermal or electrical, and their correlation to the physical performance.     

Ferroelectric,dielectric, and impedance properties of Sm-modified Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 ceramics

To investigate the effect of Sm doping on the electrical properties of Ba(Zr_0.2Ti_0.8)O₃-x(Ba_0.7Ca_0.3)TiO₃ (BZT-xBCT) (x = 40, 50, 60) ceramics, three Sm-modified ceramics were prepared using the conventional solid-state reaction method. Related electrical measurements, including ferroelectric and dielectric investigations and impedance spectroscopy, were recorded for these ceramics. It was found that a tilted morphotropic phase boundary resulted from the addition of Sm, which induced the best piezoelectric properties and insulating behaviour in the Sm-BZT-60BCT sample. An abnormal P-E loop shrinkage appeared in the Sm-BZT-50BCT sample but not in the other two samples. This could be attributable to the different electronegativities between Ca²⁺ and Ba²⁺ and between Zr⁴⁺ and Ti⁴⁺, whose contents are different in varied samples and have an effect on defect-dipole alignment as well as spontaneous polarization. The activation energies for the bulk conductivity in the three composites were calculated to be 0.28 ± 0.01, 0.08 ± 0.01, and 0.36 ± 0.01 eV, confirming the existence of oxygen vacancies in our samples. The Sm dopant is responsible for the oxygen vacancies. This also leads to an increased Curie temperature in the three composites.     

Unusual Polarization Ordering in Lanthanum Modified Lead Zirconate Titanate (Pb0.97La0.03)(Zr0.90Ti0.10)0.9925O3

Lanthanum incorporation in lead zirconate titanate (PLZT) increases the stability range of the antiferroelectric phase in the Zr‐rich side of the phase diagram. The paper presents the analysis, which has been carried out on (Pb_0.97La_0.03)(Zr_0.90Ti_0.10)_0.9925O₃ ceramic system since it exhibits interesting results with ferroelectric (FE) and antiferroelectric (AFE) phases, and coexistence of both properties in some temperature range. Transmission electron microscopy evidences a complex domain structure, where nanodomains appear within larger ones. The data are consistent with the possibility to have in this material a ferroelastic phase of novel type in which the coexistence mechanism between FE and AFE properties is associated with the oscillation in space of the polarization. The possibility for a determining role of a rigid unit mode in structural instabilities, dependence on composition and doping, and pretransitional effects in the perovskite family is underlined by the obtained results for the studied system.