Infrared Absorption Spectra and Their Correlation with the Ti-O Bond Length Variations for TiO2 (Rutile), Na-Titanates, and Na-Titanosilicate (Natisite, Na2TiOSiO4)

The mid-infrared absorption spectra (400–1200 cm −1 ) of four TiO 2 -bearing crystalline solids, in the form of rutile (TiO 2 ), Na-titanates (Na 2 Ti 6 O 13 / Na 2 Ti 3 O 7 ), and natisite (Na 2 TiOSiO 4 ), are presented, providing a clear illustration of their differences in IR band structure (band pattern). Two sharp characteristic peaks of IR absorption bands of natisite have been noted at 725 and 624 cm −1 , representing the internal vibration modes of TiO 5 (normal) and SiO 4 structural units, respectively, and obtainable by comparison with that of Ca-titanosilicate (CaTiOSiO 4 ), NTS glass (Na 2 O-TiO 2 -SiO 2 ), and low-cristobalite (SiO 2 ). The tested series of TiO 2 -bearing crystalline solids has been helpful in presenting a case study in support for the generalization of IR spectra/structure correlations, showing that vibrational spectroscopy can be useful for understanding the crystal chemistry of crystalline solids in terms of the geometric setting of molecular structural units and chemical bonds. It has been qualitatively demonstrated that the Ti-O bond length variations may be broadly correlated with the complexity of IR absorption bands of four TiO 2 -bearing solids having great diversity in both chemical composition and crystalline structure.