Elastic and mechanical properties of intrinsic and doped PbSe and PbTe studied by first-principles

Abstract

Lead chalcogenides, most notably lead selenide (PbSe) and lead telluride (PbTe), have become an active area of research due to their thermoelectric (TE) properties. The high figure of merit of these materials has brought much attention to them, due to their ability to convert waste heat into electricity. Recent efforts, such as applying pressure or doping, have shown an increase in TE efficiency. Variation in application and synthesis conditions gives rise to a need for analysis of mechanical properties of these materials. In addition to the rocksalt (NaCl) structure at ambient conditions, lead chalcogenides have an orthorhombic (Pnma) intermediate pressure phase and a higher pressure CsCl phase. By using first-principles calculations, performed within density functional theory, we study the structural, elastic and mechanical properties of PbTe and PbSe in their three phases. For each phase, elastic constants, bulk modulus, shear modulus, and Young's modulus are calculated, and the NaCl phase is studied with typical dopants, both n-type (Bi and I) and p-type (Na, In, and Tl). Pugh's ratio is employed to give insight on the brittleness of the materials and phase studied. The results presented here will be useful to guide future experiments toward the search for structurally stable TE materials.