采用还原再氧化的烧结工艺制备了0.2 mol%Y_2O_3施主掺杂的95 mol%BaTiO_3-5 mol%(Bi_(1/2)Na_(1/2))TiO_3无铅正温度系数电阻(Positive temperature coefficient of resistivity,PTCR)陶瓷。研究发现,还原气氛下烧结的样品没有明显的P...采用还原再氧化的烧结工艺制备了0.2 mol%Y_2O_3施主掺杂的95 mol%BaTiO_3-5 mol%(Bi_(1/2)Na_(1/2))TiO_3无铅正温度系数电阻(Positive temperature coefficient of resistivity,PTCR)陶瓷。研究发现,还原气氛下烧结的样品没有明显的PTCR效应,需要进一步在空气中氧化处理。其中1200℃氧化2 h的样品PTCR性能最好,电阻突跳大于3个数量级。利用交流阻抗分析方法计算了材料的晶粒、晶界电阻,发现氧化后的陶瓷晶界电阻迅速增加,而晶粒电阻基本保持不变。最后根据Heywang-Jonker理论,计算了陶瓷晶界势垒高度、势垒宽度和受主浓度。展开更多
Multiple regression equations of liquidus temperature, electrical conductivity and bath density of the Na_3AlF_6-AlF_3-BaC1_2-NaCl system were obtained from experiments by using orthogonal regression method. The exper...Multiple regression equations of liquidus temperature, electrical conductivity and bath density of the Na_3AlF_6-AlF_3-BaC1_2-NaCl system were obtained from experiments by using orthogonal regression method. The experiments were carried out in 100A cell with low melting point electrolyte, the influences of cathodic current density, electrolytic temperature, density differences of bath and liquid aluminum on current efficiency (CE) were studied; when the electrolyte cryolite ratio was 2.5, w(BaC1_2) and w(NaCl) were 48% and 10%, respectively, CE reached 90% and specific energy consumption was 10.97k Wb/kg/kg. Because of the fact that aluminum metal obtained floated on the surface of molten electrolyte, this electrolysis method was then defined as low temperature aluminum floating electrolysis. The results showed that the new low temperature aluminum electrolysis process in the Na_3AlF_6-AlF_3-BaC1_2-NaCl bath system was practical and promising.展开更多
Layered P2–Na_(2/3)Ni_(1/3)Mn_(2/3)O_2 is a promising cathode material. It exhibits a high capacity and suitable operating voltage and undergoes a phase transition from P2 to O2 during charge/discharge.Researchers ha...Layered P2–Na_(2/3)Ni_(1/3)Mn_(2/3)O_2 is a promising cathode material. It exhibits a high capacity and suitable operating voltage and undergoes a phase transition from P2 to O2 during charge/discharge.Researchers have used Ti substitution to improve the cathode, yet the chemical principles that underpin elemental substitution and functional improvement remain unclear. To clarify these principles, we used in situ Raman spectroscopy to monitor chemical changes in P2–Na2/3 Ni1/3 Mn1/3 Ti1/3 O2 and P2–Na_(2/3)Ni_(1/3)Mn_(2/3)O_2 during charge/discharge. Based on the change in the A_(1g) and E_g peaks during charge/discharge, we concluded that Ti substitution compressed the transition metal layer and expanded the planar oxygen layer in the unit cell. Titanium stabilized the P2 phase structure, which improved the cycling stability of P2–NaNMT. Our results provide clear theoretical support for future research on modifying electrodes by elemental substitution.展开更多
In order to obtain thermoelectric materials with high figure of merit, theconcept of Hollow (Vacuum) Quantum Structure or Effect and related thermoelectric materials designwere proposed. To demonstrate the theory, the...In order to obtain thermoelectric materials with high figure of merit, theconcept of Hollow (Vacuum) Quantum Structure or Effect and related thermoelectric materials designwere proposed. To demonstrate the theory, the materials of (Bi_(0.15)Sb_(0.85))_2Te_3 with porousstructure have been fabricated. Their thermoelectric properties and the microstructure wereinvestigated and compared with their density structure. It was found that the porous structure couldimprove their properties greatly.展开更多
Low-temperature sintered(Na_(1/2)Bi_(1/2))_(0.935)Ba_(0.065)Ti_(0.975)(Fe_(1/2)Nb_(1/2))_(0.025)O_(3)(NBT-BT-0.025FN)lead-free incipient piezoceramics were investigated using high-purity Li_(2)CO_(3) as sintering aids...Low-temperature sintered(Na_(1/2)Bi_(1/2))_(0.935)Ba_(0.065)Ti_(0.975)(Fe_(1/2)Nb_(1/2))_(0.025)O_(3)(NBT-BT-0.025FN)lead-free incipient piezoceramics were investigated using high-purity Li_(2)CO_(3) as sintering aids.With the ≤0.5 wt%Li_(2)CO_(3) addition,the introduced Li^(+) cations precede to enter the A-sites of the perovskite lattice to compensate for the A-site deficiencies.Once the addition exceeds 0.5 wt%,the excess Lit cations will occupy B-sites and give rise to the generation of oxygen vacancies,which accelerate the mass transport and thus lower the sintering temperature effectively from 1100℃ down to 925℃.It was also found that a small amount of Lit addition has little effect on the phase structure and electromechanical properties of the system,but overweight seriously disturbs these characteristics because of the large lattice distortion.The sintered NBT-BT-0.025FN incipient piezoceramics with 1.25 wt%Li_(2)CO_(3) addition at 925℃ provides a large strain of 0.33% and a corresponding large signal piezoelectric coefficient d_(33)^(*) of 550 pm/V at 60 kV/cm,indicating this system is a very promising candidate for lead-free co-fired multilayer actuator application.展开更多
This work designs a new system(1-x)Na_(0.5)Bi_(0.5+y)TiO_(3-x)NaTaO_(3)with a nonstoichiometric bismuth ratio,which is used as dielectrics of ceramics capacitors.Phase structure evolution of(1-x)Na_(0.5)Bi_(0.5+y)TiO_...This work designs a new system(1-x)Na_(0.5)Bi_(0.5+y)TiO_(3-x)NaTaO_(3)with a nonstoichiometric bismuth ratio,which is used as dielectrics of ceramics capacitors.Phase structure evolution of(1-x)Na_(0.5)Bi_(0.5+y)TiO_(3-x)NaTaO_(3)is characterized using XRD,Raman and TEM.Dielectric and resistant properties of(1-x)Na_(0.5)Bi_(0.5+y)TiO_(3-x)NaTaO_(3)are investigated with increasing concentration of NaTaO_(3).With these in-vestigations,the structure and defect chemistry of(1-x)Na_(0.5)Bi_(0.5+y)TiO_(3-x)NaTaO_(3)are rationalized and their respective impact on capacitor properties are elucidated.The optimized composition 0.8Na_(0.5)Bi_(0.51)TiO_(3)-0.2NaTaO_(3)possesses an ultra-wide operating temperature range(-92e398C),in which both stable permittivity and low dielectric loss is obtained.Furthermore,the fabrication of multilayer ceramics capacitors(MLCC)based on 0.8Na_(0.5)Bi_(0.51)TiO_(3)-0.2NaTaO_(3)dielectrics is investigated.With the addition of sintering aids,0.8Na_(0.5)Bi_(0.51)TiO_(3)-0.2NaTaO_(3)could be co-fired with Ag at 910℃in air,and the low temperature co-fired ceramic(LTCC)capacitors maintain good temperature stability of permittivity and low dielectric loss in-100-352℃.Therefore,our work provides a new route for pre-paring ultra-wide operating temperature capacitors at low manufacturing costs.展开更多
Ceramics based on(Na_(1/2)B_(1/2))TiO_(3) are promising candidates for actuator applications because of large strains generated by an electric field-induced phase transition.For example,the(1-x)(Na_(1/2)Bi_(1/2))TiO_(...Ceramics based on(Na_(1/2)B_(1/2))TiO_(3) are promising candidates for actuator applications because of large strains generated by an electric field-induced phase transition.For example,the(1-x)(Na_(1/2)Bi_(1/2))TiO_(3)-xSrTiO_(3) system exhibits a morphotropic phase boundary at x=0.2-0.3,leading to high values of inverse piezoelectric constant d_(33),which can be further improved by the use of single crystals.In our previous work,single crystals of (Na_(1/2)B_(1/2))TiO_(3)-SrTiO_(3) and (Na_(1/2)Bi_(1/2))TiO_(3)-TiO_(3) were grown by the solid state crystal growth technique.Growth in the(Nai/2Bi/2)TiO3-SrTiO3 system was sluggish whereas the (Na_(1/2)B_(1/2))TiO_(3)-CaTiO_(3) single crystals grew well.In the present work,0.8(Na_(1/2)Bi_(1/2))Ti0_(3)-0.2(Sr_(1-x)Ca_(x))Ti0_(3) single crystals(with x=0.0,0.1,0.2,0.3,0.4)were produced by the solid state crystal growth technique in an attempt to improve crystal growth rate.The dependence of mean matrix grain size,single crystal growth distance,and electrical properties on the Ca concentration was investigated in detail.These investigations indicated that at x=0.3 the matrix grain growth was suppressed and the driving force for single crystal growth was enhanced.Replacing Sr with Ca increased the shoulder temperature T_(s) and temperature of maximum relative permittivity T_(max),causing a decrease in inverse piezoelectric properties and a change from normal to incipient ferroelectric behavior.展开更多
Na_(1/2)Bi_(1/2)TiO_(3)-based materials exhibit potential for applications in high-power ultrasonics.The com-posites of Na_(1/2)Bi_(1/2) TiO_(3)-yBaTiO_(3)(NBTyBT;y denotes mole%)with ZnO inclusions were demonstrated ...Na_(1/2)Bi_(1/2)TiO_(3)-based materials exhibit potential for applications in high-power ultrasonics.The com-posites of Na_(1/2)Bi_(1/2) TiO_(3)-yBaTiO_(3)(NBTyBT;y denotes mole%)with ZnO inclusions were demonstrated to stabilize a ferroelectric equilibrium that led to enhanced thermal depolarization temperature(T_(d))and increased mechanical quality factor(Q_(m)).This work addresses the influence of the matrix NBTyBT phase by investigating two limiting choices based on symmetry(tetragonal/rhombohedral)and polar(relaxor/ferroelectric)nature.While the composites constituting the tetragonal NBT9BT(non-ergodic relaxor at room temperature)matrix phase exhibit improved T d,the critical temperatures in the composites with rhombohedral NBT3BT(displaying spontaneous ferroelectric order at room temperature)exhibit only marginal changes.Further,NBT3BT composites feature a 45%increase in Q m,while the corresponding increase is roughly three-fold for the NBT9BT composites.A 3-D Finite Element Method is used to simulate the electric field gradient at the matrix/inclusion interface,with the effective field distribution estimated to be higher than the applied field for highly conducting ZnO inclusions.The electrical properties indicate that,while the deviatoric stress at the matrix/inclusion interface stabilizes the ferroelectric equilibrium for the relaxor matrix phase,the stresses disrupt the long-range order for the ferroelectric matrix phase.These results establish the volume-limit of the second phase to stabilize a ferroelectric equilibrium,in addition to substantiating the role of residual stress evidenced by changes in the polar nature.Finally,a comparison of the composites with different NBTyBT phases is presented,with NBT6BT:ZnO composites demonstrating an optimal increase in both T_(d) and Q_(m).展开更多
Quenching lead-free Na_(1/2)Bi_(1/2)TiO_(3)-based ceramics from sintering temperature is established to increasethe depolarization temperature,Td and the lattice distortion.In situ synchrotron X-ray diffractionmeasure...Quenching lead-free Na_(1/2)Bi_(1/2)TiO_(3)-based ceramics from sintering temperature is established to increasethe depolarization temperature,Td and the lattice distortion.In situ synchrotron X-ray diffractionmeasurements were carried out on furnace cooled and quenched Na_(1/2)Bi_(1/2)TiO_(3)-BaTiO_(3)(NBT-BT)with 6and 9 mol.%BT to discern the field-induced ferroelectric order.Phase fractions were determined fromfull pattern Rietveld refinements and utilized together with the change in unit cell volume to calculatevolumetric strain resulting from phase transformations.NBT-6BT demonstrates a cubic symmetry in thefurnace cooled state but quenching stabilizes the rhombohedral R3c phase and delays the formation of afield-induced,long range-ordered tetragonal phase,thereby shifting the onset of macroscopic strain tohigher fields.A field-induced phase transition from a weakly distorted rhombohedral to tetragonal phasecan be observed in furnace cooled NBT-9BT.However,this phase transition cannot be detected inquenched NBT-9BT,since the ferroelectric tetragonal P4mm phase is stabilized in the initial state.Incontrast to the furnace cooled materials,both the quenched compositions exhibit overall negligiblevolumetric strain as a function of electric field.Furthermore,scanning electron micrographs of chemi-cally etched,poled and unpoled samples reveal an increased lamellar domain contrast in the quenchedmaterials.All these findings strengthen the hypothesis of a stabilized ferroelectric order resulting in theabsence of a field-induced phase transformation in quenched NBT-BT.展开更多
文摘采用还原再氧化的烧结工艺制备了0.2 mol%Y_2O_3施主掺杂的95 mol%BaTiO_3-5 mol%(Bi_(1/2)Na_(1/2))TiO_3无铅正温度系数电阻(Positive temperature coefficient of resistivity,PTCR)陶瓷。研究发现,还原气氛下烧结的样品没有明显的PTCR效应,需要进一步在空气中氧化处理。其中1200℃氧化2 h的样品PTCR性能最好,电阻突跳大于3个数量级。利用交流阻抗分析方法计算了材料的晶粒、晶界电阻,发现氧化后的陶瓷晶界电阻迅速增加,而晶粒电阻基本保持不变。最后根据Heywang-Jonker理论,计算了陶瓷晶界势垒高度、势垒宽度和受主浓度。
基金the financial supports from the Natural Science Foundation of Hunan Province,China(No.2020JJ5102)the Scientific Research Fund of Hunan Provincial Education Department,China(No.19A111).
基金The project was financially supported by the National Natural Science Foundation of China! (Gmnt No.59574018)China Postdocto
文摘Multiple regression equations of liquidus temperature, electrical conductivity and bath density of the Na_3AlF_6-AlF_3-BaC1_2-NaCl system were obtained from experiments by using orthogonal regression method. The experiments were carried out in 100A cell with low melting point electrolyte, the influences of cathodic current density, electrolytic temperature, density differences of bath and liquid aluminum on current efficiency (CE) were studied; when the electrolyte cryolite ratio was 2.5, w(BaC1_2) and w(NaCl) were 48% and 10%, respectively, CE reached 90% and specific energy consumption was 10.97k Wb/kg/kg. Because of the fact that aluminum metal obtained floated on the surface of molten electrolyte, this electrolysis method was then defined as low temperature aluminum floating electrolysis. The results showed that the new low temperature aluminum electrolysis process in the Na_3AlF_6-AlF_3-BaC1_2-NaCl bath system was practical and promising.
基金supported by the NSFC (21905239, 21925404, and 21775127)the Natural Science Foundation of Shanxi Province of China (201901D211265)the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi (2019L0609)。
文摘Layered P2–Na_(2/3)Ni_(1/3)Mn_(2/3)O_2 is a promising cathode material. It exhibits a high capacity and suitable operating voltage and undergoes a phase transition from P2 to O2 during charge/discharge.Researchers have used Ti substitution to improve the cathode, yet the chemical principles that underpin elemental substitution and functional improvement remain unclear. To clarify these principles, we used in situ Raman spectroscopy to monitor chemical changes in P2–Na2/3 Ni1/3 Mn1/3 Ti1/3 O2 and P2–Na_(2/3)Ni_(1/3)Mn_(2/3)O_2 during charge/discharge. Based on the change in the A_(1g) and E_g peaks during charge/discharge, we concluded that Ti substitution compressed the transition metal layer and expanded the planar oxygen layer in the unit cell. Titanium stabilized the P2 phase structure, which improved the cycling stability of P2–NaNMT. Our results provide clear theoretical support for future research on modifying electrodes by elemental substitution.
基金This work was financially supported by National Natural Science Foundation of China (No.5O042014 and 60176004)
文摘In order to obtain thermoelectric materials with high figure of merit, theconcept of Hollow (Vacuum) Quantum Structure or Effect and related thermoelectric materials designwere proposed. To demonstrate the theory, the materials of (Bi_(0.15)Sb_(0.85))_2Te_3 with porousstructure have been fabricated. Their thermoelectric properties and the microstructure wereinvestigated and compared with their density structure. It was found that the porous structure couldimprove their properties greatly.
基金the generous support by the National Natural Science Foundation of China under grant no.51672092 and U1732117by the Project of Henan Province Science and Technology(Grant No.172102210380)+1 种基金China Postdoctoral Science Foundation funded project no.2018M632847the generous support by Wuhan Morning Light Plan of Youth Science and Technology(No.2017050304010299).
文摘Low-temperature sintered(Na_(1/2)Bi_(1/2))_(0.935)Ba_(0.065)Ti_(0.975)(Fe_(1/2)Nb_(1/2))_(0.025)O_(3)(NBT-BT-0.025FN)lead-free incipient piezoceramics were investigated using high-purity Li_(2)CO_(3) as sintering aids.With the ≤0.5 wt%Li_(2)CO_(3) addition,the introduced Li^(+) cations precede to enter the A-sites of the perovskite lattice to compensate for the A-site deficiencies.Once the addition exceeds 0.5 wt%,the excess Lit cations will occupy B-sites and give rise to the generation of oxygen vacancies,which accelerate the mass transport and thus lower the sintering temperature effectively from 1100℃ down to 925℃.It was also found that a small amount of Lit addition has little effect on the phase structure and electromechanical properties of the system,but overweight seriously disturbs these characteristics because of the large lattice distortion.The sintered NBT-BT-0.025FN incipient piezoceramics with 1.25 wt%Li_(2)CO_(3) addition at 925℃ provides a large strain of 0.33% and a corresponding large signal piezoelectric coefficient d_(33)^(*) of 550 pm/V at 60 kV/cm,indicating this system is a very promising candidate for lead-free co-fired multilayer actuator application.
基金supported by National Natural Science Foundation of China(51972265,52272121)the Innovation Capability Support Program of Shaanxi(Program No.2021KJXX-30)the German Ministry of Education and Research(BMBF)for funding the Young Investigator Group HTL-NBT within the program“NanoMatFutur”(Grant No.03XP0146).
文摘This work designs a new system(1-x)Na_(0.5)Bi_(0.5+y)TiO_(3-x)NaTaO_(3)with a nonstoichiometric bismuth ratio,which is used as dielectrics of ceramics capacitors.Phase structure evolution of(1-x)Na_(0.5)Bi_(0.5+y)TiO_(3-x)NaTaO_(3)is characterized using XRD,Raman and TEM.Dielectric and resistant properties of(1-x)Na_(0.5)Bi_(0.5+y)TiO_(3-x)NaTaO_(3)are investigated with increasing concentration of NaTaO_(3).With these in-vestigations,the structure and defect chemistry of(1-x)Na_(0.5)Bi_(0.5+y)TiO_(3-x)NaTaO_(3)are rationalized and their respective impact on capacitor properties are elucidated.The optimized composition 0.8Na_(0.5)Bi_(0.51)TiO_(3)-0.2NaTaO_(3)possesses an ultra-wide operating temperature range(-92e398C),in which both stable permittivity and low dielectric loss is obtained.Furthermore,the fabrication of multilayer ceramics capacitors(MLCC)based on 0.8Na_(0.5)Bi_(0.51)TiO_(3)-0.2NaTaO_(3)dielectrics is investigated.With the addition of sintering aids,0.8Na_(0.5)Bi_(0.51)TiO_(3)-0.2NaTaO_(3)could be co-fired with Ag at 910℃in air,and the low temperature co-fired ceramic(LTCC)capacitors maintain good temperature stability of permittivity and low dielectric loss in-100-352℃.Therefore,our work provides a new route for pre-paring ultra-wide operating temperature capacitors at low manufacturing costs.
基金supported by the Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education under Grant No.2015R1D1A1A01057060the support of the National Research Foundation(NRF)of Korea funded by the Ministry of Science and ICT(MSIT)(Grant No.NRF-2018R1A5A1025224).
文摘Ceramics based on(Na_(1/2)B_(1/2))TiO_(3) are promising candidates for actuator applications because of large strains generated by an electric field-induced phase transition.For example,the(1-x)(Na_(1/2)Bi_(1/2))TiO_(3)-xSrTiO_(3) system exhibits a morphotropic phase boundary at x=0.2-0.3,leading to high values of inverse piezoelectric constant d_(33),which can be further improved by the use of single crystals.In our previous work,single crystals of (Na_(1/2)B_(1/2))TiO_(3)-SrTiO_(3) and (Na_(1/2)Bi_(1/2))TiO_(3)-TiO_(3) were grown by the solid state crystal growth technique.Growth in the(Nai/2Bi/2)TiO3-SrTiO3 system was sluggish whereas the (Na_(1/2)B_(1/2))TiO_(3)-CaTiO_(3) single crystals grew well.In the present work,0.8(Na_(1/2)Bi_(1/2))Ti0_(3)-0.2(Sr_(1-x)Ca_(x))Ti0_(3) single crystals(with x=0.0,0.1,0.2,0.3,0.4)were produced by the solid state crystal growth technique in an attempt to improve crystal growth rate.The dependence of mean matrix grain size,single crystal growth distance,and electrical properties on the Ca concentration was investigated in detail.These investigations indicated that at x=0.3 the matrix grain growth was suppressed and the driving force for single crystal growth was enhanced.Replacing Sr with Ca increased the shoulder temperature T_(s) and temperature of maximum relative permittivity T_(max),causing a decrease in inverse piezoelectric properties and a change from normal to incipient ferroelectric behavior.
文摘Na_(1/2)Bi_(1/2)TiO_(3)-based materials exhibit potential for applications in high-power ultrasonics.The com-posites of Na_(1/2)Bi_(1/2) TiO_(3)-yBaTiO_(3)(NBTyBT;y denotes mole%)with ZnO inclusions were demonstrated to stabilize a ferroelectric equilibrium that led to enhanced thermal depolarization temperature(T_(d))and increased mechanical quality factor(Q_(m)).This work addresses the influence of the matrix NBTyBT phase by investigating two limiting choices based on symmetry(tetragonal/rhombohedral)and polar(relaxor/ferroelectric)nature.While the composites constituting the tetragonal NBT9BT(non-ergodic relaxor at room temperature)matrix phase exhibit improved T d,the critical temperatures in the composites with rhombohedral NBT3BT(displaying spontaneous ferroelectric order at room temperature)exhibit only marginal changes.Further,NBT3BT composites feature a 45%increase in Q m,while the corresponding increase is roughly three-fold for the NBT9BT composites.A 3-D Finite Element Method is used to simulate the electric field gradient at the matrix/inclusion interface,with the effective field distribution estimated to be higher than the applied field for highly conducting ZnO inclusions.The electrical properties indicate that,while the deviatoric stress at the matrix/inclusion interface stabilizes the ferroelectric equilibrium for the relaxor matrix phase,the stresses disrupt the long-range order for the ferroelectric matrix phase.These results establish the volume-limit of the second phase to stabilize a ferroelectric equilibrium,in addition to substantiating the role of residual stress evidenced by changes in the polar nature.Finally,a comparison of the composites with different NBTyBT phases is presented,with NBT6BT:ZnO composites demonstrating an optimal increase in both T_(d) and Q_(m).
基金This research used resources of the Advanced Photon Source,a U.S.Department of Energy(DOE)Office of Science User Facility,operated for the DOE Office of Science by Argonne National Labo-ratory under Contract No.DE-AC02-06CH11357JJ and RB acknowledge support from the National Science Foundation(DMR-2004455)+1 种基金LKV,AKF and AW thank the Deutsche For-schungsgemeinschaft(DFG)for financial support under Nos.KO 5948/1-1 and KL 615/34-1(Grant No.414311761)The authors thank Maximilian Gehringer and Till Fromling for assistance with the experiment at the Advanced Photon Source.
文摘Quenching lead-free Na_(1/2)Bi_(1/2)TiO_(3)-based ceramics from sintering temperature is established to increasethe depolarization temperature,Td and the lattice distortion.In situ synchrotron X-ray diffractionmeasurements were carried out on furnace cooled and quenched Na_(1/2)Bi_(1/2)TiO_(3)-BaTiO_(3)(NBT-BT)with 6and 9 mol.%BT to discern the field-induced ferroelectric order.Phase fractions were determined fromfull pattern Rietveld refinements and utilized together with the change in unit cell volume to calculatevolumetric strain resulting from phase transformations.NBT-6BT demonstrates a cubic symmetry in thefurnace cooled state but quenching stabilizes the rhombohedral R3c phase and delays the formation of afield-induced,long range-ordered tetragonal phase,thereby shifting the onset of macroscopic strain tohigher fields.A field-induced phase transition from a weakly distorted rhombohedral to tetragonal phasecan be observed in furnace cooled NBT-9BT.However,this phase transition cannot be detected inquenched NBT-9BT,since the ferroelectric tetragonal P4mm phase is stabilized in the initial state.Incontrast to the furnace cooled materials,both the quenched compositions exhibit overall negligiblevolumetric strain as a function of electric field.Furthermore,scanning electron micrographs of chemi-cally etched,poled and unpoled samples reveal an increased lamellar domain contrast in the quenchedmaterials.All these findings strengthen the hypothesis of a stabilized ferroelectric order resulting in theabsence of a field-induced phase transformation in quenched NBT-BT.
