溶胶凝胶法制备BiFeO_3纳米颗粒及其磁性质研究
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摘要
多铁性材料是一种因为结构参数有序而导致铁电性(反铁电性)、铁磁性(反铁磁性)、铁弹性同时存在的多功能材料。铁酸铋(BiFeO3)作为一种典型的单相多铁性材料,具有远高于室温的反铁磁奈尔温度(TN)和铁电居里温度(Tc),是目前唯一在室温条件下同时表现出铁电性与磁性的材料。已有的研究表明BiFeO3的磁结构比较特殊,其基态是反铁磁态,磁相变发生在TN~643K。然而中子散射实验揭示BiFeO3反铁磁自旋序是不均匀的,呈现一种空间调制结构,其自旋表现为非公度正弦曲线排列,波长(或周期)约为~62nm。这一调制结构会导致各个离子磁矩相互抵消,使得宏观尺寸的BiFeO3在室温下仅表现出很弱的反铁磁性,严重阻碍了其实际应用的发展。
本文主要采用溶胶凝胶法制备BiFeO3纳米颗粒,并研究溶胶蒸干温度、超声辐射以及Eu离子掺杂对BiFeO3纳米颗粒的微结构、成分以及磁性质的影响,具体研究内容如下:
1)我们采用溶胶凝胶法,在不同的溶胶蒸干温度(80和150oC)以及相同的烧结温度(550oC)下,分别制备了两种BiFeO3纳米颗粒。X射线衍射(XRD)数据表明,两种样品具有相似的BiFeO3结构。虽然两种样品均表现出室温的铁磁性,然而150oC蒸干的样品磁性要远大于80oC蒸干的样品。利用高分辨率透射电子显微镜(HRTEM)和X射线光电子能谱(XPS)对样品进行测试,可以发现增强的磁性来源于溶胶在较高温度蒸干过程中所产生的γ-Fe2O3杂相,并且该杂相在经过550oC烧结后仍然保留在样品中。我们的研究结果表明在溶胶凝胶法制备BiFeO3纳米颗粒的过程中,溶胶蒸干温度对于BiFeO3纳米颗粒的成相起着至关重要的作用。相关工作已投稿至Materials Chemistry and Physics。
2)我们将超声辐射引入到溶胶凝胶法制备BiFeO3纳米颗粒的实验工艺中。研究表明:与未经超声辐射处理的样品相比,超声辐射后的样品室温铁磁性得到了明显的增强。通过对不同样品进行不同气氛条件下的后退火处理,并结合XRD、HRTEM、XPS等测试手段,我们分析了超声辐射在增强BiFeO3纳米颗粒磁性方面的作用主要体现在两个方面,一是超声辐射导致BiFeO3纳米颗粒尺寸减小;二是超声辐射导致BiFeO3纳米颗粒表面存在氧空位。相关工作已投稿至Nanotechnology。
3)我们采用溶胶凝胶法并结合快速热退火工艺制备了不同Eu掺杂量的BiFeO3纳米颗粒。采用XRD、拉曼散射谱(Raman)、傅立叶红外透射光谱(FTIR)、XPS等测试手段对样品的微结构进行表征,发现Eu掺杂导致样品的晶格发生明显的扭曲。同时我们还发现,样品的磁性也会随着Eu掺杂量的增加而增强,这主要归因于样品晶格的扭曲以及磁性Eu3+离子与Fe3+离子之间的磁性耦合。相关工作已在Applied Physics Letter上发表,并被Virtual Journal of Nanoscale Science & Technology收录。
Multiferroics are multifunctional materials which exhibit coexistence of ferroelectricity (or antiferroelectricity), ferromagnetism (or antiferromagnetism) and ferroelasticity. As a typical single-phase multiferroic, bismuth ferrite (BiFeO3) of perovskite structure is one of few candidates exhibiting room-temperature ferroelectric and G-type antiferromagnetic properties. The magnetic structure of BiFeO3 is antiferromanetic and the magnetic phase transition occurs at TN ~ 643K. However, with the help of neutron scattering measurement, the antiferromagnetic spin order of BiFeO3 has an incommensurate spiral spin structure (the period length of ~62 nm), which does not allow a net magnetization in bulk BFO.
In this dissertation, BiFeO3 nanoparticles were prepared by sol-gel method with tartaric acid used as chelant. The structure, composition and magnetic properties of BiFeO3 nanoparticles were studied in details. The main contents in the dissertation are listed in the following:
1) BiFeO3 nanoparticles have been synthesized by a sol-gel method with different gel-drying temperatures at 80oC and 150 oC respectively. X-ray diffraction (XRD) patterns showed that both samples formed similar single phase of perovskite structure after annealing at 550oC. However, much higher magnetization was observed in the sample derived from higher gel-drying temperature. Combined with transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) measurements, it was confirmed that the enhanced magnetization was attributed to the presence ofγ-Fe2O3 secondary phase, which was actually nucleated during the process of gel-drying and remained in the subsequent annealing process. Our results showed that the gel-drying temperature was critical for the formation ofγ-Fe2O3 nuclei during the sol-gel fabrication of BiFeO3 nanoparticles. This work has been submitted to Materials Chemistry and Physics.
2) BiFeO3 nanoparticles was prepared by sol-gel method with assistance of ultrasonic radiation. The magnetization of such sample was higher than that of BiFeO3 nanoparticles synthesized without ultrasonic radiation. By annealing the samples in oxygen atmosphere and vacuum, it was confirmed that the enhancement of magnetization could be attributed to the combined effect of oxygen vacancies and particle sizes. This work was submitted to Nanotechnology.
3) Bi1?xEuxFeO3 (BEFOx, x=0, 0.05, 0.075, 0.10 and 0.15) nanoparticles were prepared by a sol-gel method followed by rapid liquid-phase sintering process. XRD, TEM, Raman scattering spectra, Fourier transform infrared spectra and XPS were used to identify the effect of Eu dopant on structural and composition of the samples. It was found that the doping of Eu has caused noticeable lattice distortion of samples. An enhancement in magnetization for BEFOx samples was also observed with the increase of Eu doping concerntrations, which was ascribed mainly to lattice distortion and the contribution of the magnetically active characteristic of Eu3+ ions. This work was published in Applied physics letter and embodied by Virtual Journal of Nanoscale Science & Technology.
本文主要采用溶胶凝胶法制备BiFeO3纳米颗粒,并研究溶胶蒸干温度、超声辐射以及Eu离子掺杂对BiFeO3纳米颗粒的微结构、成分以及磁性质的影响,具体研究内容如下:
1)我们采用溶胶凝胶法,在不同的溶胶蒸干温度(80和150oC)以及相同的烧结温度(550oC)下,分别制备了两种BiFeO3纳米颗粒。X射线衍射(XRD)数据表明,两种样品具有相似的BiFeO3结构。虽然两种样品均表现出室温的铁磁性,然而150oC蒸干的样品磁性要远大于80oC蒸干的样品。利用高分辨率透射电子显微镜(HRTEM)和X射线光电子能谱(XPS)对样品进行测试,可以发现增强的磁性来源于溶胶在较高温度蒸干过程中所产生的γ-Fe2O3杂相,并且该杂相在经过550oC烧结后仍然保留在样品中。我们的研究结果表明在溶胶凝胶法制备BiFeO3纳米颗粒的过程中,溶胶蒸干温度对于BiFeO3纳米颗粒的成相起着至关重要的作用。相关工作已投稿至Materials Chemistry and Physics。
2)我们将超声辐射引入到溶胶凝胶法制备BiFeO3纳米颗粒的实验工艺中。研究表明:与未经超声辐射处理的样品相比,超声辐射后的样品室温铁磁性得到了明显的增强。通过对不同样品进行不同气氛条件下的后退火处理,并结合XRD、HRTEM、XPS等测试手段,我们分析了超声辐射在增强BiFeO3纳米颗粒磁性方面的作用主要体现在两个方面,一是超声辐射导致BiFeO3纳米颗粒尺寸减小;二是超声辐射导致BiFeO3纳米颗粒表面存在氧空位。相关工作已投稿至Nanotechnology。
3)我们采用溶胶凝胶法并结合快速热退火工艺制备了不同Eu掺杂量的BiFeO3纳米颗粒。采用XRD、拉曼散射谱(Raman)、傅立叶红外透射光谱(FTIR)、XPS等测试手段对样品的微结构进行表征,发现Eu掺杂导致样品的晶格发生明显的扭曲。同时我们还发现,样品的磁性也会随着Eu掺杂量的增加而增强,这主要归因于样品晶格的扭曲以及磁性Eu3+离子与Fe3+离子之间的磁性耦合。相关工作已在Applied Physics Letter上发表,并被Virtual Journal of Nanoscale Science & Technology收录。
Multiferroics are multifunctional materials which exhibit coexistence of ferroelectricity (or antiferroelectricity), ferromagnetism (or antiferromagnetism) and ferroelasticity. As a typical single-phase multiferroic, bismuth ferrite (BiFeO3) of perovskite structure is one of few candidates exhibiting room-temperature ferroelectric and G-type antiferromagnetic properties. The magnetic structure of BiFeO3 is antiferromanetic and the magnetic phase transition occurs at TN ~ 643K. However, with the help of neutron scattering measurement, the antiferromagnetic spin order of BiFeO3 has an incommensurate spiral spin structure (the period length of ~62 nm), which does not allow a net magnetization in bulk BFO.
In this dissertation, BiFeO3 nanoparticles were prepared by sol-gel method with tartaric acid used as chelant. The structure, composition and magnetic properties of BiFeO3 nanoparticles were studied in details. The main contents in the dissertation are listed in the following:
1) BiFeO3 nanoparticles have been synthesized by a sol-gel method with different gel-drying temperatures at 80oC and 150 oC respectively. X-ray diffraction (XRD) patterns showed that both samples formed similar single phase of perovskite structure after annealing at 550oC. However, much higher magnetization was observed in the sample derived from higher gel-drying temperature. Combined with transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) measurements, it was confirmed that the enhanced magnetization was attributed to the presence ofγ-Fe2O3 secondary phase, which was actually nucleated during the process of gel-drying and remained in the subsequent annealing process. Our results showed that the gel-drying temperature was critical for the formation ofγ-Fe2O3 nuclei during the sol-gel fabrication of BiFeO3 nanoparticles. This work has been submitted to Materials Chemistry and Physics.
2) BiFeO3 nanoparticles was prepared by sol-gel method with assistance of ultrasonic radiation. The magnetization of such sample was higher than that of BiFeO3 nanoparticles synthesized without ultrasonic radiation. By annealing the samples in oxygen atmosphere and vacuum, it was confirmed that the enhancement of magnetization could be attributed to the combined effect of oxygen vacancies and particle sizes. This work was submitted to Nanotechnology.
3) Bi1?xEuxFeO3 (BEFOx, x=0, 0.05, 0.075, 0.10 and 0.15) nanoparticles were prepared by a sol-gel method followed by rapid liquid-phase sintering process. XRD, TEM, Raman scattering spectra, Fourier transform infrared spectra and XPS were used to identify the effect of Eu dopant on structural and composition of the samples. It was found that the doping of Eu has caused noticeable lattice distortion of samples. An enhancement in magnetization for BEFOx samples was also observed with the increase of Eu doping concerntrations, which was ascribed mainly to lattice distortion and the contribution of the magnetically active characteristic of Eu3+ ions. This work was published in Applied physics letter and embodied by Virtual Journal of Nanoscale Science & Technology.
引文
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[2] Valase K J, Phys. Rev., 1920, 15, 537.
[3] Muller H, Phys. Rev., 1940, 57, 829.
[4] Cochran W, Phys. Rev. Lett., 1959, 3, 412.
[5] Scott J F and Paz de Araujo C A, Science, 1989, 246, 4936, 1400.
[6] Schmid H, Ferroelectrics, 1994, 162, 1, 317.
[7] Hill N A, J Phys Chem B, 2000, 104, 29, 6694.
[8] Fiebig M, Lottermoser T, Frohlich D, Goltsev A V, and Pisarev R V, Nature, 2002, 419, 6909, 818.
[9] Spaldin N A and Fiebig M, 2005, 309, 5733, 391.
[10] Fiebig M, Lottermoser T, Frohlich D, Goltsev A V, and Pisarev R V, Nature, 2002, 419, 6909, 818.
[11] Landau L D and Lifshitz E M, Electrodynamics of continuous media, 1960.
[12] Dzyaloshinskii E, Sov.Phys.-JETP, 1960, 10, 628.
[13] Cox D E, Shapiro S M, Cowley R A, Eibschutz M, and Guggenheim H J, Phys. Rev. B, 1979, 19, 11, 5754.
[14] Eerenstein W, Mathur N D, and Scott J F, Nature, 2006, 442, 7104 759.
[15]王克锋,刘俊明,王雨,科学通报,2008, 53, 10, 1098.
[16] Kubel F and Schmid H, Acta Cryst. B, 1990, 46, 6 698.
[17] Hill N A and Rabe K M, Phys. Rev. B, 1999, 59, 13, 8759.
[18] Reyes A, de la Vega C, Fuentes M E, and Fuentes L, J. Eur. Ceram. Soc., 2007, 27, 13-15, 3709.
[19] Zhao T, Scholl A, Zavaliche F, Lee K, Barry M, Doran A, Cruz M P, Chu Y H, Ederer C, Spaldin N A, Das R R, Kim D M, Baek S H, Eom C B, and Ramesh R, Nat Mater, 2006, 5, 10, 823.
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