Observation of the structural phase transition in SrFio3 by diffuse electron scattering

Abstract

Thermal streaks were first observed in electron diffraction patterns by Honjo et al and were attributed to low frequency acoustic waves. Recently Hua et al have also used electron diffraction to invetsigate phonons in NiAs and KCP.Strontium titanate (SrTiO3) has a perovskite structure, and is of interest because it undergoes a second order displacive structural phase transition at above 110K. Below the transition temperature, the structure changes to tetragonal with a unit cell (a, a, 2 c) , the c-axis being slightly elongated with c/a=1.0006. This structural phase transition is believed to be due to the softening of the phonon at the (111) Brillouin zone boundary, i.e. q=(lll)/2. The detailed phonon dispersion has been measured by neutron workers (for example, see 5), and is shown in Fig. 1. The phonon dispersion shows a characteristic dip at q=( 111 )/2, which is further lowered (softening) as the temperature decreases till the transition temperature is reached.