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Study on modification of novel single-phase doped multiferroic materials

Author: WuZuoHua
Tutor: ChenXiaoBing
School: Yangzhou University
Course: Microelectronics and Solid State Electronics
Keywords: Iron material The remnant polarization Remanent magnetization Ferroelectric properties New functional materials Hysteresis loop Magnetic properties Lattice distortion Ceramic samples Doping modification Ferroelectric domain The magnetic ordering Ceramics Oxygen vacancies Doping content The maximum value Solid phase sintering method X-ray diffraction analysis XRD Dielectric temperature spectrum
CLC: TM271
Type: Master's thesis
Year: 2013
Downloads: 42
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Abstract

Single-phase multiferroic materials simultaneously exhibit both ferroelectric and spin orders, which enable them to have potential applications in both magnetic and ferroelectric devices. Single-phase magnetoelectric materials still faces many difficulties. First, the coexistence of ferroelectricity and magnetism in one system has been proven very difficult. Second, an efficient coupling between the two orders in a multiferroic system seems to be even more important than their coexistence, because such a magnetoelectric coupling reprsents the basis for multi-control of the two orders by either an electric field or magnetic field. As for the trends toward device miniaturization and high-density data storage, an integration of multifunction’s into one material system has become highly desirable. The relatively smaller remanent polarization and lower piezoelectric activity of pure Aurivillius members such as Bi4Ti3O12are not satisfactory when compared with PZT film in high-density integration of memory cell and assure sensors applications. The main purposes of this dissertation are aimed at studying properties of ceramic materials after doping. It can be summarized into following three parts:(1)The polycrystalline Bi5-xEuxFe0.5Co0.5Ti3O15(BEFCT-x:x=0,0.35,0.55,0.85) ceramics were prepared by a solid state reaction method. Their structure-property relations were investigated. The crystal structure of the samples was determined by X-ray diffraction (XRD). There were no secondary phases identified by XRD. The remanent polarization2Pr firstly increased and then decreased with the increase of Eu content (x). The remanent polarization reached a maximum value of11.2μC/cm2when x=0.55. The competition mechanism between the decrease of oxygen vacancies and the deterioration of bismuth oxide layers was analyzed. The remanent magnetization increased to a maximum value of0.28emu/g with increasing of the Eu content, due to the joint effects of lattice mismatch, enhanced ferromagnetic coupling and intergrowth contribution. The measurements of dielectric permittivity showed that the thermal stability of the samples does not deteriorate. Eu doping is associated with oxygen vacancies or other point defects.(2) Bi5-xNdxFe0.5Co0.5Ti3O15(BNFCT-x:x=0.2,0.4,0.6,0.8) and Bi5-xDyFe0.5Co0.5Ti3O15(BDFCT-x:x=0.2,0.4,0.6,0.8) ceramics were prepared by solid state reaction method. Their structure-property relations were investigated. The crystal structures of the samples were determined by X-ray diffraction (XRD). There were no secondary phases identified by XRD within the limitation of the diffractometer. The remanent magnetization of BNFCT ceramics increased to a maximum value of0.58emu/g with the increase of Nd content and BDFCT ceramics reach to a maximum value of0.53emu/g with the increase of Dy content. They are not only very close, but also two orders of magnitude larger than that of non-doped ceramics. Magnetisim may come from the coupling between Fe3+and Co3+ions and lattice distortion. The remanent polarization (2Pr) increased with the increase of Nd content (x) and the maximum value is17.45μC/cm2when x=0.8. The remanent polarization (2Pr) decreased with the increase of Dy content (x) and lager then without doping ceramic sample. The remanent polarization reached a maximum value of19.28μC/cm2when x=0.2. The trend is caused by doping together with the lattice distortion and charge compensation. They effectively improve the multiferroic materials of ferroelectric and ferromagnetic.(3) SrBi3Fe1-xCoxNb2O12ceramics were prepared by a solid state reaction method. Their structure-property relations were investigated. The crystal structure of the samples was determined by X-ray diffraction (XRD). There were no secondary phases identified by XRD. The remanent polarization (2Pr) increased with the increase of Co content (x) and then decreased. The remanent polarization value is4.54μC/cm2when x=0.2. The remanent polarization (2Pr) increased with the increase of Co content (x) and the maximum value is15.3μC/cm2when x=0.8. The remanent magnetization increased to a maximum value of0.49emu/g with increasing the Co content. Magnetic mainly from the coupling between Fe3+and Co3+ions. Overall consideration, samples’ electronic and magnetic performance is best when x=0.15. It can be seen that doping of Co is obvious to improve the performance of the samples.

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