Raman and infrared spectral analysis of thallium niobyl phosphates: Tl2NbO2PO4, Tl3NaNb4O9(PO4)2 and TlNbOP2O7

Abstract

Raman and infrared spectra of Tl 2 NbO 2 PO 4 , Tl 3 NaNb 4 O 9 (PO 4 ) 2 and TlNbOP 2 O 7 are reported. The observed bands are assigned in terms of vibrations of NbO 6 octahedra and PO 4 tetrahedra in the first two compounds and in terms of NbO 6 octahedra and P 2 O 7 4− anion in the third compound. The NbO 6 octahedra in all the title compounds are found to be corner-shared and distorted. The higher wavenumber values of the ν 1 (NbO 6 ) mode and other stretching modes indicate that the NbO 6 octahedra in them are distorted in the order TlNbOP 2 O 7 > Tl 2 NbO 2 PO 4 > Tl 3 NaNb 4 O 9 (PO 4 ) 2 . The splitting of the ν 3 (PO 4 ) mode indicates that PO 4 tetrahedra is distorted more in Tl 2 NbO 2 PO 4 than in Tl 3 NaNb 4 O 9 (PO 4 ) 2 . The symmetry of P 2 O 7 4− anion in TlNbOP 2 O 7 is lowered. Bands indicate that the P-O-P bridge in the above compound has a bent P-O-P bridge configuration.

Crystal structure and vibrational properies of Rb2MgWO2(PO4)2—A new framework phosphate

“…The n 1 and n 3 modes of the PO 4 3À ion are observed at 898-947 and 967-1201 cm À1 , respectively. The frequency of the n 3 (PO 4 ) modes is higher than that observed for the titanyl (990-1130 cm À1 ) [21][22][23] and niobyl phosphates (1000-1140 cm À1 ) [24,25]. Since the study of Na SuperIonic Conductor (NASICON)-type phosphates revealed frequency increase with increasing covalent character of the metal-oxygen bonds within M-O-P bridge [26], the observed frequency increase in Rb 2 MgWP can be explained as a result of stronger covalent character of the W-O bonds when compared with the Nb-O and Ti-O bonds.…”

“…For a free WO 6 octahedron with the O h symmetry three bending modes should be observed: n 4 (F 1u ), n 5 (F 2g ) and n 6 (F 2u ). The former studies of a number of phosphates showed that the n 4 (PO 4 ) modes are usually well separated from the n 2 (PO 4 ) modes, giving rise to bands in the 490-670 cm À1 region [24][25][26][27]. In case of Rb 2 MgWP we may unambiguously assign the group of bands in the 540-660 cm À1 region to the n 4 (PO 4 ) modes.…”

“…It has been shown that the strongest Raman line can be attributed to the n 1 symmetric stretching mode of the TiO 6 (NbO 6 ) unit. This band shifts towards higher frequency with increasing ion valency (from 650-710 cm À1 for TiO 6 to around 870-890 cm À1 for NbO 6 [21][22][23][24][25]). In the present crystal a very strong Raman band at 913 cm À1 can unambiguously be assigned to the n 1 (WO 6 ) mode.…”

“…The former studies of a number of titanyl and niobyl phosphates showed that the n 1 and n 3 modes of the PO 4 3À ions are observed around 933-1000 and 970-1150 cm À1 , respectively [21][22][23][24][25]. The stretching modes of TiO 6 and NbO 6 octahedra were located in the 600-850 and 630-890 cm À1 region, respectively [21][22][23][24][25]. It has been shown that the strongest Raman line can be attributed to the n 1 symmetric stretching mode of the TiO 6 (NbO 6 ) unit.…”

Application of Gettering Process on the Improvement of the Structural and Mineralogical Properties of Tunisian Phosphate Rock

“…Raman bands are observed at 139, 169, 214, 234, 265 and 283 cm -1 . These bands are assigned to lattice vibrations as it was reported by many authers [11,18,32].…”