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JOËL MARTIAL BALKOULGA, ANTOINE BERE, VIWANOU HOUNKPATI, JUN CHEN & PIERRE RUTERANA

Abstract

The multiferroic RMnO3 (R= Rare earth) are extensively investigated because of their critically important physical properties, as well as their potential applications in spintronics. Due to their magnetocaloric properties, they are also adequate for magnetic refrigeration in the low temperature regime. Most importantly, as refrigerants, they provide an electrical insulation combined with high chemical and mechanical stability. Such critical properties at the basis of the applications mainly depend on the local structure and chemistry. Therefore, the mechanical properties of manganite perovskites RMnO3 (R=Tb, Dy, Ho and Er) have been studied by atomic simulation using the density-functional theory (DFT) as interatomic potential implemented in the Quantum Espresso code. For each perovskite RMnO3, the hexagonal (h-RMO) and orthorhombic (o-RMO) crystal structures have been considered, and the bulk modulus (B), the elastic constants (Cij), the shear’s modulus (G), Young’s modulus (E), the Poisson’s ratio (ν), the Pugh’s ratio (B/G), the universal anisotropy index (AU), and the Debye temperature (θD), have been calculated. As a result, a relation between the plastic behaviour and the crystal structures has been established. The perovskites RMnO3 tend to be brittle in the hexagonal phase (1.35 ≤ B/G ≤ 1.39) and ductile in the orthorhombic phase (1.85 ≤ B/G ≤ 2.00). The high values of the Young’s modulus, 281 GPa ≤ E ≤ 300 GPa for h-RMO and 237 GPa ≤ E ≤ 251 GPa for o-RMO, indicate that the investigated systems are solid materials. The values of the Poisson’s ratio found between 0.21 and 0.28 reflect their ionic character. The values of the universal anisotropy index, 0.47 ≤ AU ≤ 0.74 for h-RMO and 0.09 ≤ AU ≤ 0.15 for o-RMO, indicate that their mechanical anisotropy is higher for h-RMO than o-RMO, and the elastic anisotropy is better for o-RMO than h-RMO.

RMnO3, manganite perovskites, elastic constants, mechanical properties, DFT, quantum espresso,