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Synthesis and characterisation of nanostructured neodymium titanium oxides by sol-gel process: Controlling the phase composition, crystal structure and grain size

Mohammadi, M. R ; Sharif University of Technology | 2010

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  1. Type of Document: Article
  2. DOI: 10.1016/j.matchemphys.2010.03.036
  3. Publisher: 2010
  4. Abstract:
  5. Nanocrystalline neodymium titanium oxide thin films and powders with different phase compositions with mesoporous structure were produced by a straightforward particulate sol-gel route. The sols were prepared in various Nd:Ti molar ratios and they showed a narrow particle size distribution in the range 20-26 nm. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powders contained mixtures of Nd4Ti9O24, Nd2Ti4O11, Nd3Ti4O12 for titanium dominant powders (Nd:Ti ≤ 45:60), mixtures of Nd2TiO5 and Nd2O3 for neodymium dominant powders (Nd:Ti ≥ 75:25) and pure Nd3Ti4O12 phase for equal molar ratio of Nd:Ti, depending on the annealing temperature and Nd:Ti molar ratio. Moreover, it was found that Nd:Ti molar ratio influences the preferable orientation growth of the neodymium titanium oxide compounds. Transmission electron microscope (TEM) images confirmed that the average crystallite size of the powders annealed at 400 °C was in the range 1.0-2.8 nm and a gradual increase was occurred up to 6.7 nm by heat treatment at 1000 °C. The activation energy of crystal growth reduced with a decrease of Nd:Ti molar ratio, calculated in the range 6.90-18.12 kJ mol-1. Low activation energies indicating that the grain size will not change much with increase in temperature. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had uniform, mesoporous and nanocrystalline structure. Moreover, atomic force microscope (AFM) images presented that the thin films had a columnar like morphology with average grain size in the range 17-30 nm at 600 °C and 47-60 nm at 800 °C, depending upon the Nd:Ti molar ratio. Based on Brunauer-Emmett-Taylor (BET) analysis, the synthesized powders showed mesoporous structure containing pores with sphere like shapes. The surface area of the powders was enhanced by increasing Nd:Ti molar ratio and reached as high as 110 m2 g-1 for the powder containing Nd:Ti = 75:25 (molar ratio) at 400 °C. In addition, the mesoporous structure of the powders was stable at high annealing temperatures up to 900 °C
  6. Keywords:
  7. Neodymium titanium oxide ; Sol-gel ; Annealing temperatures ; Atomic force microscopes ; Average grain size ; Characterisation ; Field emission scanning electron microscopes ; Grain size ; Low-activation energy ; Mesoporous ; Mesoporous structures ; Molar ratio ; Nano-crystalline structures ; Nano-structured ; Nanocrystalline ; Nanocrystallines ; Orientation growth ; Sol-gel routes ; Surface area ; Synthesized powder ; TiO ; Titanium oxide thin films ; Transmission electron microscope ; Activation energy ; Annealing ; Crystal structure ; Crystallite size ; Electron microscopes ; Field emission ; Fourier transform infrared spectroscopy ; Fourier transforms ; Gels ; Grain boundaries ; Grain size and shape ; Nanocrystalline powders ; Neodymium compounds ; Oxide films ; Phase composition ; Scanning electron microscopy ; Sol-gel process ; Sol-gels ; Sols ; Spheres ; Thin films ; Titanium ; Titanium oxides ; Transmission electron microscopy ; Vapor deposition ; Wavelet transforms ; X ray diffraction ; X ray powder diffraction ; Neodymium
  8. Source: Materials Chemistry and Physics ; Volume 122, Issue 2-3 , 2010 , Pages 512-523 ; 02540584 (ISSN)
  9. URL: http://www.sciencedirect.com/science/article/pii/S0254058410002427?np=y