Preceding paraphases in “diffuse transition” ferroelectrics

We report experimental studies of the onset of hard-mode Raman activity in some AB′ x B″1−x O3-type compounds related closely to the perovskites. The first order Ramanscattering seems to appear due to a phase transition at high temperatures into Fm3m space group from the Pm3m paraphase. We believe that the existence of several phases preceding a ferroelectric one determines a specific behavior of AB′B″O3-type compounds which is well-known as a “diffuse phase transition”.