Mechanical properties of layered tilkerodeite (Pd2HgSe3) and jacutingaite (Pt2HgSe3) crystals: insights on the interlayer, intralayer interactions, and phonons

Abstract

Tilkerodeite and jacutingaite are layered minerals promising for low-power nano-spintronic devices due to their robust topological phases and air stability. Their intralayer and interlayer mechanical properties, of paramount importance for real applications, are here unveiled by first-principles calculations. Their stiffness coefficients, which confirm their lattice stability, and interlayer force constants show that tilkerodeite is weaker against intralayer deformations, slightly difficult to exfoliate, and less lubricant than jacutingaite. Jacutingaite aggregates are more stiff, incompressible, and resistant to shape-change deformations than tilkerodeite, while the latter is more ductile than the former. The wavenumber shifts between corresponding vibration modes in these materials show that tilkerodeite is less stiff than jacutingaite against the atomic displacement of optical silent, infrared- and Raman-active modes, while the opposite was found for their low-frequency breathing and shear rigid-layer modes. Our findings advance the knowledge on the structural properties of new quantum spin Hall materials, key for their use, and explained the unexpected wavenumber redshift of the tilkerodeite Raman spectrum relative to that of jacutingaite observed in experiments.