Raman scattering and X‐ray diffraction on YBiTi₂O₇ prepared at low temperature

Abstract

The conditions of preparation of a pure YBiTi 2 O 7 phase by sol-gel were optimised. A single phase was obtained at temperature as low as 800°C when triethanolamine/diethanolamine was used as additional ligands. The expected composition was confirmed by energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). YBiTi 2 O 7 exhibits the pyrochlore structure with a unit-cell parameter of 10.2117(5)Å. This structure was confirmed by Raman spectroscopy, which revealed a shift of the main E g mode towards lower wavenumbers when bismuth is introduced in the structure. Broad bands were observed for all the recorded spectra, which characterise rather a disorder due to bismuth III cations in the structure than an effect of particle size. This study confirmed the possibility to lower the temperature of preparation of pyrochlores containing bismuth, which could be of interest as photocatalyst for the decomposition of organic and toxic materials.

Raman study of phonon modes in bismuth pyrochlores

“…8 The Raman band around 430 cm −1 also has similar frequencies to other pyrochlores. 13,14,16,19,21,22,24,26 This mode is attributed mostly to the B-O stretch force constant. 12,13,27 The fact that the Ta samples shows higher frequencies for this mode also suggests stronger force constants in the octahedra for BZT and BMT than for BZN and BMN.…”

“…This analysis would explain the trend, also present in the IR, of higher frequencies observed for the lighter B cation in BZN and BMN, than for BMT and BZT. However, based on Fischer's calculations, and the proximity of an F 2g mode to the E g mode in other pyrochlores, 10,[12][13][14][19][20][21][22]25,26,28,29 we have assigned the ϳ300 cm −1 feature in the Raman spectrum to the E g mode and one of the F 2g modes. The A 1g , and one of the F 2g modes of the ideal structure are assigned to bands at 530 cm −1 and 420 cm −1 , respectively.…”

“…The appearance of the additional Raman bands, which correspond to Raman-inactive modes of the ideal pyrochlore structure, confirms the displacive disorder of the A and OЈ sites in the bismuth pyrochlores. The Raman modes were assigned by reference to the Raman spectra of many other pyrochlores, [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] some of which include lattice-dynamical calculations, 12,27,28 and firstprinciples calculations. 11 In the literature, the lattice dynamical and ab initio calculations show an interesting difference.…”

“…Each mode was studied and assigned by first referencing the literature on diverse samples with structures close to the ideal pyrochlore structure. 10,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] Then, the bands were also compared to our ab initio calculations for Bi 2 Ti 2 O 7 and those in the literature for Cd 2 Nb 2 O 7 . 11 Table II shows the frequencies of the various observed modes for the four samples along with their assignment.…”

Recent advances in linear and non‐linear Raman spectroscopy. Part III

“…Other temperature-dependent Raman scattering studies were carried out by Saraiva et al [151] on the Na 2 MoO 4 crystal and by Chiang et al [152] on iron perchlorate hexahydrate (Fe(ClO 4 ) 2 · 6H 2 O). Raman scattering and X-ray diffraction studies on YBiTi 2 O 7 and on analcime and pollucite were carried out by Garbout et al [153] and Presser et al, [154] respectively.…”