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.

A comparative ab initio study on mechanical and thermal properties of rare-earth scandate LnScO3 (Ln = La, Pr, Nd, Sm, Eu and Tb) compounds

“…However, this number can be further reduced when the crystalline symmetry of the solid material is taken into account. Rareearth scandates with orthorhombic symmetry have nine independent elastic coefficients that can be computed, such as C [19][20][21]. In our calculation and experimental data [20,21], the relationship between the lattice constants is c < a < b (standard setting), whereas in the experimental and theoretical study [19], a < b < c (non-standard setting) [2].…”

“…In the literature, there are no study on elastic constants expect for NdScO 3 , SmScO 3 and TbScO 3 compounds. If we compare the calculated elastic constant values of the NdScO 3 , SmScO 3 and TbScO 3 compounds with the experimental values [20,21], the difference between the other constants except the C 66 constant is about 0.5%-12%. C 66 is about 22%-24%.…”

“…Rareearth scandates with orthorhombic symmetry have nine independent elastic coefficients that can be computed, such as C [19][20][21]. In our calculation and experimental data [20,21], the relationship between the lattice constants is c < a < b (standard setting), whereas in the experimental and theoretical study [19], a < b < c (non-standard setting) [2]. When the elastic constants of materials with orthorhombic structure are compared with the literature, the standard or nonstandard representation between the lattice constants should be taken into account.…”

“…Pestka et al [19] measured elastic coefficients of single-crystal NdScO 3 and SmScO 3 compounds grown by the Czochralski method using resonant ultrasound spectroscopy (RUS) together with the theoretical ab-initio calculation method. The elastic coefficients of the NdScO 3 , SmScO 3 and TbScO 3 compounds were investigated by RUS measurements at room temperature [20,21]. In recent years, nanoscale semiconductor devices have gained importance in the electronics world.…”

“…As far as we know, the elastic coefficients of rare-earth scandate compounds have not yet been systematically investigated. Until now, only elastic coefficients of NdScO 3 , SmScO 3 and TbScO 3 compounds have been measured using RUS [19][20][21] in combination with ab-initio method [19]. However, theoretical and experimental works to understand the thermal and mechanical properties of LnScO 3 compounds contain very insufficient and limited information.…”