An alternative to Rietveld method for phase determination of Ce-TiO2 materials

GRAVINA ANABELA NOEL; D'ELÍA NOELIA LAURA; SARTUQUI JAVIER; MESSINA PAULA VERÓNICA

San Pablo

Congreso; XXII Brazilian Crystallographic Association Meeting and I Latin American Crystallographic Association Meeting; 2015

The importance of phase content in Ce-TiO2 materials is a widely known fact due to its importance in thermal stability, heterogeneous catalytic properties and even in bioactivity. In this work we present a thorough analysis of phase composition that can be used to select the appropriate synthesis conditions in order to obtain the desired properties for a wide range of application. A microemulsion mediated route has been chosen to synthesize Ce-TiO2 materials, using n-heptane/n-butanol/CTAB/water system as a reactor and Titanium Isopropoxide (TTIP) and Cerium Valerate (Ce(Val)3) as inorganic precursors; final products were obtained after hydrothermal treatment, purification and calcination, according to the procedure described in a previous report [1]. Different Ce(Val)3/TTIP ratios were used in the range of 6.0 x 10-4 to 0.30 as well as different calcination temperatures: 100, 200, 400, 700, 800, 900 °C. Pure TiO2 and no calcination were used as control conditions. Phase determination from XRD data is a rather complex procedure and full fitting performed using Rietveld Quantitative Analysis (RQA) is often the method of choice, but it requires certain precision in the knowledge of crystal parameters which is usually very difficult when dealing with poorly structured materials. Also, the use of an internal standard is needed when trying to quantify the amorphous content that implies further sample processing. In this work we present a phase analysis performed using a less demanding method based on peak deconvolution inspired in the determination of cellulose crystallinity index [2]. Certain assumptions have been made such as Voigt function for the peaks shape and the amorphous content was assigned to the wide peak at 20° and considered responsible of peak broadening. Validation of the method has also been performed by contrast with others such as the widely used method of Spurr and Myers, which gives the Anatase/Rutile ratio, and the Rietveld refinement did by Matӗjová et al. [3] to determine the Amorphous/Anatase/Cerianite ratio in CeO2-TiO2 materials. In both cases, the differences were smaller than 1 %.