## 3 Results and Discussion
### X-Ray Photoelectron Spectroscopy (XPS)  
XPS analysis was employed to determine the chemical composition and valence states of the ions in the samples. C 1s was used as the reference for the calibrations of the spectra of the other elements. The two survey spectra are shown in Figure 4. The main difference  
Figure 3: Vibration bands in Raman spectra of thermally treated samples. The arrows and red frames highlight the increasing intensities of the 446, 488, and 668 cm\({}^{-1}\) bands. The blue shift from the 342 cm\({}^{-1}\) band in the LTA sample to 337 cm\({}^{-1}\) in the LTA-Pt sample is indicated by red numbers. between the samples is the presence of the Pt core level and Auger electron peaks in the spectral shapes of La, Ti, and O. In the Ti 2p spectrum of the LTA sample (Figure 5a), two components are identified. The peak at approximately 458 eV is characteristic of Ti\({}^{4+}\)[9; 26; 27; 40]. A second peak at a higher binding energy, around 460 eV, may be attributed either to a different TiO\({}_{2}\) phase than that present in the La\({}_{2}\)Ti\({}_{2}\)O\({}_{7}\) structure or to a non-stoichiometric TiO\({}_{x}\) phase [68]; however, it is unlikely to correspond to Ti\({}^{3+}\), since Ti\({}_{2}\)O\({}_{3}\) is typically detected at lower binding energies. Moreover, the peak at the lower binding energy could be assigned to a La-O-Ti component, while the higher energy peak would correspond to TiO\({}_{2}\); alternatively, as attributed by [PERSON] et al. [21] for La\({}_{2}\)Ti\({}_{2}\)O\({}_{7}\) powders forming rectangular nanosheets, the additional peaks observed at higher binding energies around 460 eV and 465 eV could be from the unsaturated Ti of TiO\({}_{5}\) motifs on the Ti-terminated facet of the La\({}_{2}\)Ti\({}_{2}\)O\({}_{7}\) nanostructures. The spin-orbit splitting (SOS) is 5.7 eV, consistent with the Ti\({}^{4+}\) oxidation state. Furthermore, the presence of this additional component may reflect differences between Ti\({}^{4+}\) species on the surface and in the bulk of the sample. The O 1s region of the LTA sample (Figure 5b) can be deconvoluted into four peaks, corresponding to La-O/Ti-O bonds at 529.34 eV [9; 27; 40], TiO\({}_{2}\) (or TiO\({}_{x}\)) at 530.72 eV, C=O and/or OH groups at 531.94 eV [16; 39], and C-O bonds at 533.48 eV, respectively [16; 21]. The La 3d spectrum (Figure 5c) of the LTA sample exhibits a spin-orbit splitting of 16.9 eV between the La 3d\({}_{5/2}\) and La 3d\({}_{3/2}\) peaks, confirming the presence of La\({}^{3+}\)[21; 40]. Component c2 (green line in Figure 5c), observed at approximately 835-836 eV, corresponds to the \"antibonding\" orbitals. Component c4 (orange line in Figure 5c), centered around 848 eV, exhibits a broad profile and is attributed to plasmonic loss [69]. Furthermore, the \"multiplet splitting\" of the La chemical state in this sample (6.6 eV) is larger than the typical values reported for La\({}_{2}\)O\({}_{3}\) (4.6 eV) and La\({}_{2}\)Ti\({}_{2}\)O\({}_{7}\) (4.3 eV) [26]. The C 1s region is deconvoluted into three distinct peaks (Figure 5d). The peak at 284.6 eV is assigned to C-C bonds, typically arising from carbon contamination on the sample surface. The peak at 286.27 eV corresponds to C=O functional groups, while the peak at 289.07 eV is attributed to O-C=O bonds, indicative of carbonate species. This is consistent with the tendency of lanthanum compounds to form surface carbonates under ambient conditions. Figure 4: XPS survey spectra (black line—LTA sample; blue line—LTA-Pt sample). The Ti 2p XPS spectrum for the LTA-Pt sample is presented in Figure 6a. The spectrum of the doped sample exhibits a single chemical state of Ti\({}^{4+}\), characterized by a Ti 2p\({}_{3/2}\) peak at 458.32 eV. The spin-orbit splitting (SOS) of 5.7 eV between the Ti 2p\({}_{3/2}\) and Ti 2p\({}_{1/2}\) peaks further confirms the exclusive presence of Ti\({}^{4+}\). It is worth mentioning that the additional peak observed around 460 eV is no longer detectable.