Synthesis And Properties Investigation Of TbFe_xMn_1-xO₃

Perovskite oxides have been the focus of many researchers because of their fruitful physical properties, such as multiferroics, Colossal Magnetoresistance (CMR) effect , catalysis property, and so on. TbMnO₃ is a kind of multiferroic materials with perovskite structure, the unique magnetic structure and electric polarization properties of TbMnO₃ leads to a strong magnetoelectric effect. And many researchers are also focus on perovskite type TbFeO₃ since it has the photocatalytic activity. In this dissertation, TbMnO₃, TbFeO₃ and TbFe_xMn_1-xO₃ nanoparticles have been prepared and their properties were investigated systematically. The main points are summarized as follows:(1) A modified polyacrylamide gel route was used to fabricate TbMnO₃ nanoparticles. It is demonstrated that high-phase-purity TbMnO₃ nanoparticles can be prepared separately by using the chelating agents citric acid and ethylenediamine-tetraacetic acid (EDTA) at a sintering temperature of 800 oC. Scanning electron microscope (SEM) observation reveals that the particles prepared using citric acid as the chelating agent are regularly spherical in shape and highly uniform in size with a diameter of ⁶7 nm, while the sample prepared by using the chelating agent EDTA mainly consists of sphere-, ellipsoid-, and rod-like particles with an average particle size of ¹15 nm. In addition, it is found that adding an appropriate amount of bisacrylamide into the precursor solution can lead to a moderate reduction in particle size and a more regular particle morphology. Magnetic hysteresis loop measurements indicate that the TbMnO₃ nanoparticles exhibit paramagnetism in at room temperature.(2) A polyacrylamide gel route was used to prepare TbFeO₃ nanoparticles. X-ray diffraction (XRD) results indicate that single-phase TbFeO₃ particles can be prepared at a calcination temperature of 650oC using tartaric acid, citric acid and ethylenediamine-tetraacetic acid (EDTA) as the chelating agents. The use of acetic acid or oxalic acid as the chelating agent is difficult to achieve the synthesis of single-phase TbFeO₃ samples. Scanning electron microscope (SEM) observations reveal that the particles prepared using tartaric acid as the chelating agent are regularly spherical in shape and highly uniform in size with a small average diameter of ⁵0 nm; the particles prepared using citric acid as the chelating agent mainly exhibit sphere-like shape with an average size of ¹00nm; and the particles prepared by using the chelating agent EDTA are shaped like ellipsoid with adhesive behavior to some extent with an average size of ¹10nm. Ultraviolet (UV)-visible diffuse reflectance absorption spectra indicate that the as-prepared TbFeO₃ nanoparticles have an absorption cutoff wavelength of 590nm. It is demonstrated that the products exhibit a pronounced photocatalytic activity under UV as well as visible-light irradiation. The highest photocatalytic efficiency is observed for the tartaric acid-derived sample.(3) The TbFe_xMn_1-xO₃ nanoparticles had been synthesized by the polyacrylamide gel route. The XRD and FTIR analysis showed that the crystal structure of samples were perovskite structure (space group Pbnm), and the Fe3+ replaced Mn3+ and entered the center of the MnO6 octahedra in the Fe-doped TbMnO₃ samples. Ultraviolet (UV)-visible absorption spectra indicate that the samples arised an absorption cutoff wavelength as the Fe (x) content increases. Magnetic hysteresis loop measurements indicate that the TbFe_xMn_1-xO₃ nanoparticles exhibit paramagnetism in at room temperature.