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摘要
Inelastic neutron scattering has been used to study the transverse acoustic (TA) phonon propagating on the (0,0,1) plane polarized on this plane in BiVO4 above the ferroelastic phase transition at T-c=528 K. The energies of the TA phonon dispersion curve along [0.7 xi,xi,0] are slightly lower than those along [xi,xi,0], indicating that the acoustic symmetry direction deviates from the high-symmetry [xi,xi,0] direction. The [0.7 xi,xi,0] TA branch softens in a limited range. xi less than or similar to 0.2 as the temperature approaches T-c from above. The gradual decrease in the initial slope of the [0.7 xi,xi,0] TA branch is quite different from the complete softening of the TA mode reported from Brillouin scattering measurements. A temperature-dependent central peak is associated with the [0.7 xi,xi,0] TA mode. Furthermore, an elastic diffuse streak along [1,(1) over bar ,0] exists up to 878 K. These precursor effects are discussed in connection with the TA phonon softening.
- 出版日期2011-7-12
