## 3 Results and Discussion
### Raman Spectroscopy  
Table 2 lists the Raman shifts in both LTA-Pt and LTA, according to [9; 66] and our work. According to the literature [9], the wavenumbers of the rare-earth oxygen-stretching modes (La-O) generally lie in the region of 300-500 cm\({}^{-1}\). Some of the bands in this range are due to Ti-O vibrations or, more probably, to complex motions involving the participation of both La and Ti cations. \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Wavenumbers (cm\({}^{-1}\))**} & \multicolumn{1}{c}{**Assignments and Vibration Mode**} \\ \hline
**LTA** & **LTA-Pt** & \\ \hline
806 & 806 & Ti–O–Ti bridges in TiO\({}_{6}\) octahedra from titanate \\
776 & 772 & Ti–O stretching in TiO\({}_{6}\) octahedra from titanate \\
620 & 621 & La–O stretching and Ti–O vibrations \\
547 & 549 & La–O stretching and Ti–O vibrations \\
491 & 490 & La–O stretching vibrations and Ti–O–Ti bridges in TiO\({}_{6}\) octahedra \\
464 & 464 & La–O stretching vibrations and Ti–O bending modes \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Assignment of vibration bands in FT-IR spectra of thermally treated samples. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multicolumn{2}{c}{**Synthesized Samples**} & \multicolumn{2}{c}{**Literature for La–O and**} & \\ \cline{2-5}  & **LTA-Pt** & **LTA** & **Ti–O Bonds [64; 66]** & **Assignment to Raman Vibrations** \\ \hline
1 & 109 & 111 & 112 & La–O stretching vibration \\
2 & 129 & 131 & 131 & Ti–O bond stretching vibration for the six-fold \\  
tretching vibrations of Ti–O–Ti octahedra \\  & & & (A\({}_{\text{1g}}\) mode) \\
23 & - & 668 & - & - \\
24 & 794 & 792 & 790 & Stretching vibrations of Ti–O–Ti octahedra \\
25 & 809 & 808 & 808 & Ti–O bond stretching vibration for the six-fold \\  & & & & coordinated Ti in rutile TiO\({}_{\text{2g}}\) mode) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Assignment of Raman shifts in thermally treated samples. There are no new chemical bonds forming in the Pt-modified La\({}_{2}\)Ti\({}_{2}\)O\({}_{7}\) samples, suggesting that the dopant (Pt) might be found in the metallic form. A newly formed chemical bond would have given a vibration in the Raman spectra of the LTA-Pt. It could be the case that there is the intercalation of the Pt between the layers of the La\({}_{2}\)Ti\({}_{2}\)O\({}_{7}\) perovskite. The typical crystalline structure of monoclinic layered perovskite La\({}_{2}\)Ti\({}_{2}\)O\({}_{7}\) is observed with Raman analysis. Except the peaks at 488 and 668 cm\({}^{-1}\) from the LTA sample, the peaks at 342, 371, 405, 430, 448, 520, 541, 559, 609, and 793 cm\({}^{-1}\) correspond to the typical monoclinic layered perovskite crystalline structure [13; 67]. The increased Raman intensity at 446 cm\({}^{-1}\) in the LTA without Pt is more considerable when compared to the LTA-Pt. For LTA the 446 cm\({}^{-1}\) peak has similar intensity with the 402 cm\({}^{-1}\) peak, as in LTA-Pt, where it is less intense. As the peak appearing at 446 cm\({}^{-1}\) is related to stretching vibrations of Ti-O-Ti in the distorted [TiO\({}_{6}\)], the small disruption in crystallinity and further distortion of the TiO\({}_{6}\) may suggest the introduction of defects by Pt [9]. This tendency was already observed in the literature for the doping Na-doped LTA [9], as the intercalation of Pt between the LTA layers disrupts the crystallinity of the pure LTA. The appearance of the 668 cm\({}^{-1}\) peak in varying intensities according to the probed spot on the surface of pure LTA (LTA without Pt) is the most notable difference in the Raman spectra. This additional Raman mode at 668 cm\({}^{-1}\) marked in Figure 3 could indicate local lattice imperfections. This additional mode at 668 cm\({}^{-1}\) is close to the assigned Ti-O-Ti vibration (661 cm\({}^{-1}\)) from two-dimensional leptodrocite-type TiO\({}_{6}\) layers [64].