Role of crystal chemistry in twinning-based superelasticity in rare-earth orthophosphate ceramics

Materials that dampen vibrations while maintaining mechanical integrity are essential for enhancing the performance and lifetime of engineering components. Recently, some monazite rare earth orthophosphates (REPO4s) have been shown to dissipate mechanical energy superelastically while retaining high stiffness under diverse loading and temperature conditions. To guide REPO4 composition design for multifunctional applications, it is necessary to understand how superelastic energy dissipation varies across the monazite series and to determine whether the related xenotime-structured REPO4s exhibit similar behavior. Spherical nanoindentation was employed to probe superelastic deformation in monazite-structured compositional end members, LaPO4 and GdPO4, as well as xenotime-structured TbPO4. Superelasticity and energy dissipation were observed in both LaPO4 and TbPO4, extending the composition range beyond GdPO4 and EuPO4 compositions previously reported. Statistically significant differences in dissipated energies and onset stresses for superelasticity are discussed in terms of the interplay between crystal chemistry, bonding, and mechanical properties, providing insights into tailoring the dissipative response of REPO4 ceramics.