Junaid, Bushiri M; Jayasree, R S; Fakhfakh, M; Nayar, V U(Elsevier, 2002)
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Abstract:
Raman and infrared spectra of Tl2NbO2PO4, Tl3NaNb4O9(PO4)2 and TlNbOP2O7 are reported. The observed bands are assigned in
terms of vibrations of NbO6 octahedra and PO4 tetrahedra in the first two compounds and in terms of NbO6 octahedra and P2O7
4−
anion in the third compound. The NbO6 octahedra in all the title compounds are found to be corner-shared and distorted. The higher
wavenumber values of the ν1 (NbO6) mode and other stretching modes indicate that the NbO6 octahedra in them are distorted in the order
TlNbOP2O7 > Tl2NbO2PO4 > Tl3NaNb4O9(PO4)2. The splitting of the ν3 (PO4) mode indicates that PO4 tetrahedra is distorted more
in Tl2NbO2PO4 than in Tl3NaNb4O9(PO4)2. The symmetry of P2O7
4− anion in TlNbOP2O7 is lowered. Bands indicate that the P–O–P
bridge in the above compound has a bent P–O–P bridge configuration