Influence of conductivity on BaTiO₃ crystals phase transitions: A dilatometric study

The 3m ⇔ mm2 ⇔ 4mm ⇔ m3m phase transitions in BaTiO₃ etched dielectric and non-etched semiconducting crystals have been studied by the dilatometry and the acoustic emission simultaneously. In contrast to ceramics the dilatometric curves in the crystals studied have the form of the dosed hysteresis loops. The hysteresis loop area = temperature hysteresis × thermal expansion coefficient is shown to be a useful parameter for characterizing the phase transition. The differences in the hysteris loop areas between dielectric and semiconducting crystals are likely to be attributed to the additional energy expenditure on phase transition in defect surface layers present on the non-etched semiconducting crystals.