First‐order <i>A</i>₁(TO) phonons as evidence of disorder in BaTiO₃

Abstract

Abstract Evidence is presented, based on Raman scattering measurements, that the three modes observed in the A 1 (TO) phonon spectrum of tetragonal BaTiO 3 are first order. These results are interpreted as supporting the order‐disorder model of the ferroelectric phase transition.