Abstract
In this thesis, we have studied the correlation between dopant element and morphology of nanotubes in yttrium hydroxide. Yttrium hydroxide nanotubes, doped with cobalt or europium, were synthesized by solvent thermal method of yttrium chloride, cobalt chloride, and europium chloride. We demonstrate that the morphology of yttrium hydroxide nanotubes can be controlled by changing the dopant material and reaction temperature. The crystal structures of yttrium hydroxide host were probed by x-ray diffraction (XRD). We confirmed the host structure is in hexagonal phase. The sizes and morphologies of nanotubes were determined by field emission scanning electron microscopy (FE-SEM). Cobalt K-edge x-ray absorption near-edge structure (XANES) spectra were used to confirm that the dopant atoms do not form oxides or cluster. Extended x-ray absorption fine structure (EXAFS) technique has been employed to probe the local environments surrounding cobalt and europium in these materials. The cobalt impurity atoms were found to locate on interstitial sites. On the other hand, the europium impurity atoms were found to locate on the grain boundary of the yttrium hydroxide nanotubes. And the difference between the positions of cobalt atoms and those of europium atoms may explain why the morphologies of cobalt doped nanotubes and europium doped nanotubes are so different. The SQUID measurement at 300K reveals that the yttrium oxide nanotubes were diamagnetic. However, the nanoparticle samples, synthesized by a similar procedure, exhibit a combination of ferromagnetism and paramagnetism. That may set an upper limit of particle size in the ferromagnetic phase to insulator phase transition in DMOs system.