稀土Dy/Eu掺杂对铌酸钾钠基压电陶瓷结构与性能的影响OA

Introduction Piezoelectric ceramics are critical components in sensors,actuators,energy converters,and micro-electromechanical systems.The lead-based compositions dominate in the existing market.However,the release of lead during their lifecycle poses severe environmental and human-being health risks,which contradicts global sustainable development goals.Therefore,developing high-performance lead-free alternatives becomes a paramount research priority.Among lead-free alternatives,potassium sodium niobate((K,Na)NbO3,KNN)-based ceramics stand out due to their low driving voltage,large electrostrain,and minimal hysteresis,making them performance-competitive with conventional PZT for precision actuators.Their performance is typically enhanced by constructing polymorphic phase boundaries and regulating microstructure.However,the existing doping strategies inadvertently degrade thermal stability,which remains a key bottleneck for practical applications.Rare-earth ions act as effective modifiers in KNN-based piezoceramics.They enhance a relaxor behavior,and improve thermal stability by shifting rhombohedral-tetragonal(R-T)phase transition below room temperature,and introduce photoluminescence due to their abundant energy levels.The integration of electrostrain and luminescence in KNN-based systems is thus significant,paving a way for developing novel bimodal functional materials for next-generation optoelectronic devices.In this work,the 0.96(K0.48Na0.52)(Nb0.95Sb0.05)O3-0.04Bi0.5(Na0.82K0.18)0.5ZrO3(0.96KNNS-0.04BNKZ)composition with a polymorphic phase transition characteristic was chosen as a matrix,and rare-earth oxides(Dy2O3 and Eu2O3)served as modifiers.The effect of rare-earth oxides doping on the microstructure,ferroelectric/electrostrain properties,and photoluminescence performance of the 0.96KNNS-0.04BNKZ ceramics was investigated. Methods 0.96KNNS-0.04BNKZ-x%Dy/Eu(x=0,0.05,0.10,0.20,0.40)lead-free ferroelectric ceramics were synthesized by a solid-state reaction method.The stoichiometric raw materials were weighed according to the formula.They were then ground in ethanol in a ball mill with zirconia balls for 24 h.The powders were calcined at 850℃for 4 h,then ground again for 24 h.After drying,the powders were mixed with 10%polyvinyl alcohol(PVA)as a binder and then granulated.Subsequently,disc-shaped green compacts(with the sizes of 10 mm in diameter and 0.5 mm in thickness)were pressed and subjected to a debinding process at 550℃.The ceramics were obtained after sintering at 1130-1200℃for 2 h.After polishing,silver electrodes were fired at 650℃for electrical testing.The ceramics were sintered at at 1130℃to 1200℃for 2 h,depending on the doping levels.After polishing,silver electrodes were fired on the surfaces at 650℃for electrical characterization.The phase structure was analyzed by an X-ray diffractometer(D8 advance).The surface morphology was determined by a field emission scanning electron microscope(Merlin compact,Carl Zeiss Co.,Germany).The temperature-dependent dielectric constant was measured by a broadband dielectric spectrometer(Novocontrol concept 40).The ferroelectric and electric-field-induced strain were characterized by a ferroelectric analyzer(TF 2000)coupled with a laser interferometer(SP-S 120/500).The photoluminescence properties were evaluated by a fluorescence spectrometer(FLS920). Results and discussion Dy/Eu-doped 0.96KNNS-0.04BNKZ ceramics exhibit a single perovskite structure.At low doping levels(i.e.,x≤0.10%),the rhombohedral-tetragonal(R-T)coexisting phase maintains,while a higher doping(i.e.,x≥0.20%)induces a transition to the pseudocubic(Pc)phase,with no secondary phases appears in all the samples.All the ceramics present dense and uniform microstructures.The average grain size gradually decreases with increasing Dy/Eu doping,indicating that rare-earth ions effectively inhibit grain growth.In terms of electrical properties,a moderate Dy/Eu doping(i.e.,Dy:x=0.10%;Eu:x=0.05%)enhances ferroelectricity,as reflected by improved P-E loop squareness and increased saturated polarization(Pmax).The 0.10%Dy and 0.05%Eu samples achieve an optimal electrostrain performance,delivering unipolar strains(Suni)of 0.257%and 0.241%at 70 kV/cm,which are accompanied by large piezoelectric strain coefficients(d33*)of 367 pm/V and 344 pm/V,respectively.An appropriate doping optimizes the domain structure and facilitates domain switching in an external electric field,thereby improving both ferroelectric and electrostrain properties.In contrast,excessive doping leads to a severe lattice distortion,notably octahedral tilting,which pins domain walls and hinders their reorientation in response to the electric field,ultimately compromising ferroelectric and electrostrain performance.Furthermore,the 0.05%Dy-and 0.05 %Eu-doped ceramics exhibit excellent thermal stability,showing less than 10%variation in electrostrain at 25-100 ℃,which demonstrates their great potential for use in piezoelectric actuators.In addition,Dy/Eu doping introduces a pronounced photoluminescence to the ceramics.Under blue-light excitation,Dy3+-doped samples yield an intense yellow emission,whereas Eu3+-doped samples produce a bright orange-red emission. Conclusions The introduction of Dy/Eu could promote a phase transition from a mixed R-T phase to a Pc phase.An appropriate doping effectively enhanced the ferroelectric and electrostrain properties of the materials.Specifically,the 0.10%Dy-and 0.05%Eu-doped ceramics achieved unipolar strains(Suni)of 0.257%and 0.241%at an electric field of 70 kV/cm,with corresponding piezoelectric strain coefficients(d33*)of 367 pm/V and 344 pm/V,respectively.Furthermore,the 0.05%Dy-and 0.05%Eu-doped samples exhibited excellent thermal stability,with a variation in electrostrain of less than 10%at 25-100℃,demonstrating a great potential for piezoelectric actuator applications.In addition,Dy/Eu doping imparted outstanding photoluminescence properties to the ceramics.Under blue-light excitation,Dy3+-doped samples exhibited an intense yellow emission,while Eu3+-doped samples displayed a bright orange-red emission.The combination of electrical and luminescent characteristics could make this material a promising candidate for optoelectronic coupling devices.