Abstract
Titanium-dioxide (TiO2) is a low-cost, chemically inert material that became the basis of many modern applications ranging from, for example, cosmetics to photovoltaics. TiO2 exists in three different crystal phases − Rutile, Anatase and, less commonly, Brookite − and, in most of the cases, the presence or relative amount of these phases are essential to decide the TiO2 final application and its related efficiency. Traditionally, X-ray diffraction has been chosen to study TiO2 and provides both the phases identification and the Rutile-to-Anatase ratio. Similar information can be achieved from Raman scattering spectroscopy that, additionally, is versatile and involves rather simple instrumentation. Motivated by these aspects this work took into account various TiO2 Rutile+Anatase powder mixtures and their corresponding Raman spectra. Essentially, the method described here was based upon the fact that the Rutile and Anatase crystal phases have distinctive phonon features, and therefore, the composition of the TiO2 mixtures can be readily assessed from their Raman spectra. The experimental results clearly demonstrate the suitability of Raman spectroscopy in estimating the concentration of Rutile or Anatase in TiO2 and is expected to influence the study of TiO2-related thin films, interfaces, systems with reduced dimensions, and devices like photocatalytic and solar cells.
Highlights
Titanium dioxide TiO2, known as titania, is a semiconductor material with applications in technological fields such as: photovoltaics,[1,2] energy storage,[3] photocatalysis[4 ] with emphasis on environmental[5] and health problems,[6] optical coatings[7] and sensors,[8] just to mention a few of them.075201-2 A
The TiO2 mixtures were investigated by X-ray diffraction (XRD) and Raman scattering spectroscopy
Allied to its relative simplicity, the XRD technique is well-known by its high efficiency in determining the atomic structure-composition of materials.[23]
Summary
Titanium dioxide TiO2, known as titania, is a semiconductor material with applications in technological fields such as: photovoltaics,[1,2] energy storage,[3] photocatalysis[4 ] with emphasis on environmental[5] and health problems,[6] optical coatings[7] and sensors,[8] just to mention a few of them. X-ray diffraction (XRD) has been the preferred technique to study TiO2, efficiently exposing the presence of the Rutile, Anatase, and Brookite phases, their crystal orientation, and the Rutile-to-Anatase ratio.[11] Raman scattering spectroscopy is able to precisely distinguish between the different TiO2 crystal phases but, so far, the technique presented certain restrictions to evaluate the Rutile or Anatase concentrations Most of these shortcomings relied on:[18,19,20,21,22] (i) the recurring interest in the very strong Anatase-related phonon mode at ∼ 144 cm-1 that, is present in the Rutile phase; (ii) the study of a limited range of Rutile or Anatase concentrations precluding any reliable conclusion; and (iii) the lack of a simple relationship connecting the Rutile or Anatase contents with their respective Raman features that explains, at the same time, the whole range of concentrations. Raman spectroscopy represents a powerful characterization technique acting either identifying or computing the Rutile or Anatase phases of TiO2 that is expected to advance the research of TiO2-containing materials with dimensions in the sub-micrometers range and/or in the form of thin films
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