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

Abstract

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 SmScO3, TbScO3, and DyScO3 between 103 K and 1673 K. Our set of elastic stiffnesses shows high internal consistency, e.g., the relations c11>c33>c22, c66>c44>c55, and c13≥c12>c23 hold for all crystal species at room temperature. The structures become overall stiffer with decreasing RE-radius and increased charge density. The behavior of c44 at low temperatures indicates in all REScO3 a structural instability that might lead to an orthorhombic→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 TbScO3 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 REScO3 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 REScO3 as a substrate material, when mostly isotropic thermal expansion or longitudinal stiffness in-plane is desired, respectively.