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Vibrational analysis of the two non-equivalent, tetrahedral tungstate (WO4) units in Ce2(WO4)3 and La2(WO4)3
| Content Provider | Semantic Scholar |
|---|---|
| Author | Burcham, Loyd J. Wachs, Israel E. |
| Copyright Year | 1998 |
| Abstract | Abstract The infrared and Raman spectra of Ce2(WO4)3 and La2(WO4)3, which are complicated by the superposition of bands from two non-equivalent WO4 units, have been successfully assigned above 300 cm−1 according to Td point group symmetry. Individual assignment of the two types of tungstate units, WIO4 (C2 site symmetry) and WIIO4 (C1 site symmetry), relies on comparison with the spectra of tetrahedral reference tungstates of Na2WO4, CaWO4, and MgWO4, and on the differences between WIO4 and WIIO4 known from the crystal structure. Normal coordinate analysis indicates that the force constants for WIO4 and WIIO4 roughly correlate with the amount of deviation from ideal Td point symmetry, WIO4 being similar to CaWO4 (both mildly distorted tetrahedrons), while WIIO4 is closer to MgWO4 (both highly distorted tetrahedrons). Non-ideality is also indicated by the calculated potential energy distribution (PED), which shows a substantial degree of vibrational interaction between bonds—especially in the less symmetric WIIO4 unit. Frequency differences between IR and Raman bands that originate from the same Td point group modes are attributed mainly to factor group splitting (i.e. Raman active gerade and IR active ungerade factor group modes). However, the LO-TO polarization mixing and surface modes that generate the observed vibrational frequencies in powders may also contribute to these frequency differences, since the magnitude of these effects may not be the same in Raman as in IR. Finally, it is likely that other rare earth tungstates of stoichiometry Ln2(WO4)3, where Ln=La∼Dy, have similar vibrational spectra due to their similar structures. |
| Starting Page | 1355 |
| Ending Page | 1368 |
| Page Count | 14 |
| File Format | PDF HTM / HTML |
| DOI | 10.1016/S1386-1425(98)00036-5 |
| Volume Number | 54 |
| Alternate Webpage(s) | http://www.lehigh.edu/operando/Publications/1998%20vibrational%20analysis%20of%20WOx%20compounds.pdf |
| Alternate Webpage(s) | https://doi.org/10.1016/S1386-1425%2898%2900036-5 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
