Understanding trends in thermal hysteresis during the martensitic transformation in ZrO2-CeO2 shape-memory ceramics

ZrO₂-based shape-memory ceramics (SMCs) offer the potential for significant benefits over shape-memory alloys (SMAs), including higher transformation temperatures, work output, and environmental resistance. Despite these potential benefits, two shortcomings have prevented these materials from reaching their full potential: 1) polycrystals catastrophically crack during the martensitic transformation and 2) the transformation exhibits a large hysteresis of over 100°C. We have recently found that improved interface compatibility by meeting λ₂=1 can reduce transformation-induced cracking. However, unlike in SMAs, the hysteresis in these preferred compositions is still large, and a complete understanding of the controlling factors in SMCs is still lacking. In this work, we use calorimetry and in-situ X-ray diffraction to systematically measure thermal hysteresis and transformation crystallography in the ZrO₂-CeO₂ system. We reveal trends that cannot be explained solely by improved interface compatibility. These results are analyzed in the context of martensite nucleation theory to explain thermodynamic and kinetic aspects of hysteresis in these materials.