Thermoelastic properties of rare-earth scandates SmScO3, TbScO3 and DyScO3

The elastic properties of rare-earth scandates were only reported at room temperature based on simulations and experimental measurements with poor agreement thus far. Using resonant ultrasound spectroscopy and inductive gauge dilatometry, we determined the elastic stiffnesses, their temperature dependence, and thermal expansion coefficients of SmScO${}_3$ , TbScO${}_3$ , and DyScO${}_3$ between 103 K and 1673 K. Our set of elastic stiffnesses shows high internal consistency, e.g., the relations $c_{11}>c_{33}>c_{22}$ , $c_{66}>c_{44}>c_{55}$ , and $c_{13}\ge c_{12}>c_{23}$ hold for all crystal species at room temperature. The structures become overall stiffer with decreasing $RE$ -radius and increased charge density. The behavior of $c_{44}$ at low temperatures indicates in all $RE$ ScO${}_3$ a structural instability that might lead to an orthorhombic$\to$ monoclinic transition involving shear of the (100)-plane upon increasing pressure. The transition seems to be promoted by a decreasing $RE$ -radius. Anomalies in two mixed resistances of TbScO${}_3$ below room temperature are indicative of at least one more structural instability that may also cause a phase transition where the structure is sheared. So far, only magnetic phase transitions at about 3 K have been observed in $RE$ ScO${}_3$ in literature. The thermoelastic properties in [100] and [001] directions of all materials become increasingly isotropic at high temperatures, suggesting decreased structural tilt. (100) or (010) crystal cuts should be chosen for applications of a $RE$ ScO${}_3$ as a substrate material, when mostly isotropic thermal expansion or longitudinal stiffness in-plane is desired, respectively.