¦¡-fe <sub> 2 </ Sub> O <sub> 3 </ Sub> Raman Spectroscopy And Physical Properties Of Nanoparticles

The methods to gain Raman spectroscopy of α-Fe₂O₃ nano particles were studied. We talked about the effect of TiO2 on the Raman scattering α-Fe₂O₃ nano particles and we also explored the effect mechanism of particle size on Morin transition of α-Fe₂O₃ nano particles by its Raman spectroscopy.We could see a fluorescent peak and we couldn't observe any vibrational mode of α-Fe₂O₃ when the excitation laser is 633 run. But when α-Fe₂O₃ nano particles were pressed or were doped in TiO2 some vibrational modes of α-Fe₂O₃ could be observed.Firstly, compound particles of α-Fe₂O₃/TiO2) were prepared by Sol-gel method with an acid catalyst and their Raman spcctroscopy was measured. The results shew that TiO2 had some matrix effect on α-Fe₂O₃ nano particles and make the fluorescence of bare pareticles disappeared and some feature bands of α-Fe₂O₃ could be observed. The annealing temperature during preparation, the content of doped α-Fe₂O₃, nano particles and the particle size of α-Fe₂O₃ nano particles had effects on gaining the Raman spectroscopy of α-Fe₂O₃ nano particles. When the content of doped α-Fe₂O₃ was small, its Raman feature bands could be observed at lower annealing temperature and the feature bands would disappear at high annealing temperature. When the content of doped α-Fe₂O₃ was increased the feature bands of α-Fe₂O₃ nano particles still could be observed with the rising annealing temperature; if the annealing temperature was so high that the reaction of α-Fe₂O₃ and TiO2 happened, then Fe2TiO5 was produced. The size of α-Fe₂O₃ nano particles was smaller; TiO2 had more obvious effect on α-Fe₂O₃ The doping of α-Fe₂O₃ nano particles made the phase transition temperature of TiO2 lower, The size of α-Fe₂O₃ nano particles was smaller, the effect was more obvious.TiO2 coated α-Fe₂O₃ nano particles when compound particles were prepared by ultrasonic method with a basic catalyst. The Raman spectroscopy of α-Fe₂O₃ could be observed well. Compared with the compound particles prepared by Sol-gel method, compound particles prepared by ultrasonic method needn't be annealed and TiO2 was still amorphia, so the spectra of α-Fe₂O₃ were not affected by the strong peaks of TiO2. Jf we annealed the compound particles, the strong peaks of anatasc affected the scattering peaks of α-Fe₂O₃ but only one weak band of α-Fe₂O₃ wascovered by the bands of anatasc and the other bands of α-Fe₂O₃ could be observed.The analysis of M(?)ssbaucr spectrocopy and XPS technique shew that the coating of TiO2 changed the surface atom structure and cloud density of nano particles, then affected the fluorescent and Raman scattering character of α-Fe₂O₃ nano particles.The Raman spectra of α-Fe₂O₃ could be obtained directly when we changed the excitation light wavelength. Compared the Raman spectroscopy of nano particles with single crystal, we found that some Raman peaks shift red and broaden with the decreasing of particle size. The analysis of Mossbauer spcctrocopy proved that the red shift and broaden of bands were attributed to the minisize effect and surface effect.The study on the Morin transition (TM) of α-Fe₂O₃ nano particles shew that TM was lower the particle size smaller. We could explain this effect mechanism well according to the Raman spectra of a-Fe₂O₃ nano particles. It was because the Fe -O band length on the surface of nano particles was longer and the distribution of Fe-O bond length became wider. Then the energy of crystal field decreased with the increasing of the Fe-O bond length and it affected the the single ion anisotropy, so TM became down.