We happen to have taken some Raman scattering in Ce-Pt and La-Pt surface intermetallic compounds. We find both vibronic and electronic excitations (see linked manuscript in case you're interested).
In the vibrational (optical phonon) spectra, we see some peaks to blue shift upon lowering the temperature to ~20K (I would expect that to happen) but also one mode which exhibits a red shift.
Since these compounds have similarities with Laves phase compounds I wonder whether that is actually a known feature in such materials and am looking for literature (reviews) in this respect. So far, our search for adequate material has not been very fruitful.
Therefore I'd appreciate any helpful pointers. Otherwise, if you have ideas about why softening of optical modes (raher than hardening) might occur, your suggestions are very welcome. (In any case we are not aware of any low temperature structural transition in our compounds).
Article Study of crystal-field splitting in ultrathin CePt5 layers b...
Extended search for literature was not directly useful but directed our attention towards the cause of our observation likely to be electronic in nature (in absence of other phase transitions). As a matter of fact, the untypical behavior appears in CePt5 but not in LaPt5. Could well be then (and we happen to have some experimental hints at that) that the atypical phonon softening is a "monitor" of the formation of the heavy fermion band in CePt5, which we infer from magnetic findings (see final part of linked manuscript).
Article Kondo screening and beyond: An x-ray absorption and dichrois...
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