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Phonon Spectroscopy in Antimony and Tellurium Oxides

Publication Type
Journal Name
The Journal of Physical Chemistry A
Publication Date
Page Numbers
7869 to 7880

α-Sb2O3(senarmontite),β-Sb2O3(valentinite), andα-TeO2(paratellurite) arecompounds with pronounced stereochemically-active Sb and Te lone pairs. The vi-brational and lattice properties of each have been previously studied, but often led toincomplete or unreliable results due to modes being inactive in infrared (IR) or Ramanspectroscopy. Here, we present a study of the relationship between bonding and lat-tice dynamics of these compounds. M ̈ossbauer spectroscopy (MS) is used to study thestructure of Sb inα-Sb2O3andβ-Sb2O3, whereas the vibrational modes of Sb and Tefor each oxide are investigated using nuclear inelastic scattering (NIS) and further in-formation on O vibrational modes is obtained using inelastic neutron scattering (INS).Additionally, vibrational frequencies obtained by density functional theory (DFT) cal-culations are compared with experimental results in order to assess the validity of theutilized functional. Good agreement was found between DFT-calculated and experi-mental density of phonon states up to a 7% scaling factor. The Sb-O-Sb wagging modeofα-Sb2O3whose frequency was not clear in most previous studies is experimentallyobserved for the first time at∼340 cm−1. Softer lattice vibrational modes occur in or-thorhombicβ-Sb2O3compared to cubicα-Sb2O3, indicating that the antimony bondsare weakened upon transforming from the molecularαphase to the layer-chainedβstructure. The resulting vibrational entropy increase of 0.45±0.1kB/Sb2O3at 880 Kaccounts for about half of theα-βtransition entropy. The comparison of experimentaland theoretical approaches presented here provides a detailed picture of the latticedynamics in these oxides beyond the zone center and shows that the accuracy of DFTis sufficient for future calculations of similar material structures.