| Autor: |
Moseley DH; Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States., Juneja R; Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States., Daemen LL; Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States., Sergueev I; Deutsches Elektronen-Synchrotron DESY, D-22607 Hamburg, Germany., Steinbrügge R; Deutsches Elektronen-Synchrotron DESY, D-22607 Hamburg, Germany., Leupold O; Deutsches Elektronen-Synchrotron DESY, D-22607 Hamburg, Germany., Cheng Y; Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States., Cooper VR; Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States., Lindsay L; Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States., Kidder MK; Manufacturing Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States., Manley ME; Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States., Hermann RP; Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States. |
| Abstrakt: |
α-Sb 2 O 4 (cervantite) and β-Sb 2 O 4 (clinocervantite) are mixed valence compounds with equal proportions of Sb III and Sb V as represented in the formula Sb III Sb V O 4 . Their structure and properties can be difficult to calculate owing to the Sb III lone-pair electrons. Here, we present a study of the lattice dynamics and vibrational properties using a combination of inelastic neutron scattering, Mössbauer spectroscopy, nuclear inelastic scattering, and density functional theory (DFT) calculations. DFT calculations that account for lone-pair electrons match the experimental densities of phonon states. Mössbauer spectroscopy reveals the β phase to be significantly harder than the α phase. Calculations with O vacancies reveal the possibility for nonstoichiometric proportions of Sb III and Sb V in both phases. An open question is what drives the stability of the α phase over the β phase, as the latter shows pronounced kinetic stability and lower symmetry despite being in the high-temperature phase. Since the vibrational entropy difference is small, it is unlikely to stabilize the α phase. Our results suggest that the α phase is more stable only because the material is not fully stoichiometric. |
