Thermal Expansion of the Orthorhombic Phase in the Ln2TiO5 System

The thermal expansion behavior of the orthorhombic phase in the Ln2TiO5 (Ln = La, Nd, Gd, Dy, and Y) system was evaluated, using synchrotron X‐ray diffraction from room temperature to approximately 1500°C in air. The components of the thermal expansion tensor were calculated from the refined d‐spacings, using the program CTEAS. Subsequent analysis of the thermal expansion and crystallographic information revealed that the mechanism behind the thermal expansion was a result of strained trigonal‐bipyramidal structures overcoming an energy barrier to become more relaxed. The temperature at which a significant shift in the trigonal‐bipyramidal structure manifests was correlated with the size of the rare‐earth cation that dictates the volume of the overall cell. Larger rare‐earth cations with larger cell volumes allow more room for the trigonal‐bipyramidal structures to easily relax.