Results and discussions 3.1. Structural and morphological study
The XRD patterns of Ti1_xMnxO2 (x = 0.03, 0.05, 0.07) are shown in Fig. 2. Data estimated from the analysis of these diffractograms are tabulated in Table 1. All the diffraction peaks are well indexed
to the tetragonal anatase phase structure (JCPDS-782486) and no hint of manganese containing phases is resolved. The main anatase peak (101) shifts to lower angles with increase in manganese
concentration (inset of Fig. 2). Further an increase of the lattice c-parameter, cell volume and strain is noticed (Fig. 3 and Table 1).The observed trend in particular specifies introduction of manganese
ions in the lattice and somewhat correlates with the observation on anatase titania doped with other transition metal ions [13]. The average crystallite size are calculated by using the Debye
Scherrer’s formula d ผ 0:9kbCosh where k is the wavelength of the X-ray source used; b is the full width at half maximum (FWHM); h is the bragg diffraction angle and the dependence of grain size
on manganese incorporation is depicted in Table 1. As can be seen from the XRD patterns (inset of Fig. 1), the diffraction peak (101) gets broadened as the manganese concentration is increased suggestinga systematic decrease in grain size. For undoped TiO2 the average grain size is 18 nm (fwhm = 0.4308 radian) while it decreases to 7 nm (fwhm = 1.168) with 7% manganese incorporation. The incorporated manganese ions in the TiO2 lattice thus suppress the grain growth by interfering into the intergranules that inhibit the grain boundary mobility or alter the surface energy leading to a decrease in grain growth velocity or nucleation energy obstruction resulting in decrease in grain size [14,15].
Fig. 4a and b shows the transmission electron microscopic images of undoped and 5% Mn doped TiO2 nanoparticles. The average particle size for undoped titania is 21 nm while it decreases to 10 nm for 5% manganese doping concentration. The effect of manganese doping on the microstructural change in nanocrystalline titania is further studied by Raman Spectroscopy,
Fig. 5. Anatase TiO2 has six active Raman modes (A1g + 2- B1g + 3Eg) [16]. The intense Eg peak appears at 148 cm_1. The other Eg peak at 199 and 642 cm_1. One B1g peak appears at
398 cm_1 and the (A1g + B1g) peak appears at 520 cm_1. Compared to pure one the most intense Eg Raman peak at 146 cm_1 in manganese doped TiO2 exhibits a decrease in intensity and blue