CUBIC TO TETRAGONAL MARTENSITIC-TRANSFORMATION IN LEAD TITANATE (PBTIO3) SINGLE-CRYSTALS

The cubic to tetragonal (C/T) phase transformation in PbTiO3 single crystals has been studied in both the forward and reverse modes and found to show martensitic characteristics. Microstructural features were investigated by heating stage optical microscopy, and room temperature transmission electron microscopy. During transformation, a small hysteresis is involved. The phase front passes swiftly through the crystal and surface relief accompanying the transformation is seen. The twinning system involved was identified as a compound twin in the tetragonal phase with K1 = {110}, eta-1 = <110BAR>, K2 = {110BAR}, and eta-2 = <110>. The phase boundaries (habit planes) were frozen by controlling the temperature profile. It is found that the habit planes vary within a certain range. Not only different specimens show this real variation, but also the same specimen under different transformations follows this, indicating the importance of local arrangements near the habit plane interfaces. Theoretical predictions, with only a minute change of lattice parameters, show that experimental data appear to fit calculated results fairly well, if one considers interfacial conditions. The results show a certain degree of consistency, which implies that the martensitic phenomenological crystallographic theory applies. Discussions on the microstructural features as well as previous work on perovskite materials are presented.