Phonon Spectroscopy in Antimony and Tellurium Oxides

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 ledto incomplete or unreliable results due to modes being inactive in infrared (IR) orRaman spectroscopy. Here, we present a study of the relationship between bondingand lattice dynamics of these compounds. M ̈ossbauer spectroscopy (MS) is used tostudy the structure of Sb inα-Sb2O3andβ-Sb2O3, whereas the vibrational modes ofSb and Te for each oxide are investigated using nuclear inelastic scattering (NIS) andfurther information on O vibrational modes is obtained using inelastic neutron scatter-ing (INS). Additionally, vibrational frequencies obtained by density functional theory(DFT) calculations are compared with experimental results in order to assess the va-lidity of the utilized functional. Good agreement was found between DFT-calculatedand experimental density of phonon states with a 7% scaling factor. The Sb-O-Sbwagging mode ofα-Sb2O3whose frequency was not clear in most previous studies isexperimentally observed for the first time at∼340 cm−1. Softer lattice vibrationalmodes occur in orthorhombicβ-Sb2O3compared to cubicα-Sb2O3, indicating thatthe antimony bonds are weakened upon transforming from the molecularαphase tothe layer-chainedβstructure. The resulting vibrational entropy increase of 0.45±0.1kB/Sb2O3at 880 K accounts for about half of theα-βtransition entropy. The com-parison of experimental and theoretical approaches presented here provides a detailedpicture of the lattice dynamics in these oxides beyond the zone center and shows thatthe accuracy of DFT is sufficient for future calculations of similar material structures.