Preparation and characterization of Al/Cu doped Cerium oxide nanoparticles

• Main Authors: Chen, Sin Fu, 陳信孚
• Other Authors: Soo, Yun Liang
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/90846230100854357077

碩士 === 國立清華大學 === 物理系 === 103 === In this thesis, we study the magnetic behaviors of Al-Cu codoped CeO2 nanocrystals. The samples were synthesized by thermal decomposition method. A variety of experimental methods such as x-ray diffraction (XRD), Raman spectroscopy, x-ray absorption fine structures (XAFS), and superconducting quantum interference device (SQUID) have been used to investigate the structures and physical properties of the materials. Since the undoped CeO2, metallic copper (Cu) and aluminum (Al), as well as possible Cu or Al-based secondary phases, are not ferromagnetic, the appearance of ferromagnetism in the samples is a very intriguing research topic. Our x-ray diffraction (XRD) data shows only CeO2 peaks and therefore the possible formation of CuO and Al2O3 second phases can be excluded. This observation is also supported by the results of Raman spectroscopy and x-ray absorption near edge structure (XANES). Magnetic properties of the samples were measured by the superconducting quantum interference device (SQUID) at room temperature. The 5% Cu-doped CeO2 sample exhibits room-temperature ferromagnetism while the pure CeO2 appears to be paramagnetic. However the room-temperature ferromagnetic behavior is destroyed by the addition of Al. The XANES analysis revealed that the content of Ce3+ ions in CeO2 was largely increased by incorporating 5% of Cu dopant atoms. On the other hand, addition of Al can lead to substantial decrease of Ce3+ content. By comparing the XANES spectra of doped samples with different Cu and Al concentration, we conclude that the addition of aluminum ions can effectively change the valence state of Cu and thus destroy ferromagnetism in these materials.