“…As shown in Figure d, the pure NTO and MoNTO-10 samples exhibit the characteristic peaks of the Na 2 Ti 6 O 13 phase along with few peaks of Na 2 Ti 3 O 7 . − Meanwhile, the MoNTO-15 consists only the characteristic peaks of the Na 2 Ti 6 O 13 phase, which is in fact in accordance with the XRD results. The presence of the Na 2 Ti 3 O 7 phase can be detected by the characteristic band located at ∼306, ∼347, ∼452, ∼852, and ∼884 cm –1 , which can be ascribed to the Na–O–Ti bond stretching and scissors-type vibrations of O–Ti–O bonds. − On the other hand, the Raman spectra of the Na 2 Ti 6 O 13 phase is dominated by lower frequency bands obtained at ∼110, ∼138, ∼197, ∼225, and ∼275 cm –1 , which are very strong and well resolved. Generally, the vibrations obtained in the region below 400 cm –1 and above 600 cm –1 are related to the sodium and displacements of the TiO 6 octahedron, respectively .…”