Study On The Local Atomic Structure And Raman Spectra Of Titanium Dioxide From Anatase To Rutile

As a photocatalyst with the excellent performances in the field of clean energy,titanium dioxide has attracted more and more attention.Titanium dioxide can stably exist in the nature with two structures:a)anatase with high performances of photocatalyst,and b)rutile with promising optical properties.Anatase can be irreversibly transformed into rutile at a certain calcinated temperatures.Howe-ver,the features of structure phase transition from anatase to rutile including the local atomic environments and the atomic reconstruction are still unclear.It will severely hinder people to understanding and controlling anatase-rutile transition.Hence,in this paper,TIO2 particles prepared by sol-gel method are studied by using transmission electron microscopy,scanning electron microscopy,X-ray diffraction,laser Raman spectroscopy,and atomic pair distribution function The main results are listed as follows:(1)Quantitative analysis of XRD patterns for the sol-gel samples indicates that the initial transition temperature of anatase-rutiLe transition is?528 0C,the transition range is 528-805 0C,and the critical size of anatase crystallites is?73 nm.(2)The qualitative analysis of atomic pair distribution functions based on the electron diffraction patterns indicates that TiO6 octahedra have been formed when the gel particles were sintered at 200 0C,but with large distortions.The nearest neighboring octahedra will stack to nanocrystallites(several nanometers)as the form of cis-way.As the increase of the calcinating temperatures,distortions of Ti06 octahedra will be weakened,and more and more neighbouring octahedra will be stacked on it to form large crystallite.When the crystallite size approaches to the critical one,the crystallite will be unstable and part of octahedra will be rotated to form rutile in the form of trans-way.(3)The sieving experiment of gel particles shows that:a)the small gel particles will lead to a high initio transition temperature;b)gels with different particle sizes behavior a similar critical size of anatase crystallites.(4)Raman experiments of sol-gel samples calcinated as series temperatures indicate some characteristic scattering peaks,e.g.,Eg,B1g and A1g will be enhanced as the increase of temperature,meaning a preferred-orientation growth of anatase.