We propose a new interpretation of the 110°K phase transition in SrTi${\mathrm{O}}_3$, in which the essential feature is a soft phonon at the corner of the cubic Brillouin zone. This interpretation is supported by new evidence from the temperature-dependent Raman spectrum as well as by results of earlier experiments and calculations. Several other experimental results are explained or predicted on the basis of our model for the phase transition.

• Received 20 May 1968

DOI:https://doi.org/10.1103/PhysRevLett.21.16