The Raman spectra of Bi2Ti4O11 at hydrostatic pressure or high temperature show that the frequency of the soft mode has a non-zero value at the phase transition point. The Raman spectra of Bi1.8La0.2Ti4O11 and Bi1.8Yb0.2Ti4O11 at high pressure reveal that there is an additional phonon mode in the low-frequency region. The finite soft mode frequency has proved to arise from the coupling between the soft mode and the additional phonon mode which may be a zone boundary mode. The phase transition can be considered as a second-order ferroelastic one driven by the soft mode.
No takes yet. Share an insight, caveat, or question.
Meng et al. (1994) studied this question.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: