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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.

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