Phase Composition Characterization

Microstructural and phase analyses of the NTO powders and the coatings were carried out using X-ray diffraction (XRD: Panalytical X’Pert Pro) and Raman spectroscopy (Renishaw inVia, using a 633 nm laser source). The morphology and composition of the processed surfaces were characterized using scanning electron microscopy (SEM, FEI NOVA 230) coupled with an energy dispersive X-ray emission spectrometer (EDS, Thermo Scientific UltraDry). Finally, both elemental compositions and valence states were examined by X-ray photoelectron spectroscopy (XPS, Kratos Ultra DLD) using monochromated Al Kα radiation (15 kV, 10 mA), with a pass energy of 20 eV for high-resolution surveys. It should be noted that, prior to the XPS analysis, the sample surfaces were cleaned by Ar⁺ sputtering for 3 min to remove any surface impurities. Following XPS analysis, quantitative analysis of the spectra was carried out using the CasaXPS software.³¹