Based on first-principles calculations, we explore the electronic and phonon transport properties of a new-type two-dimensional (2D) hexagonal material XSe (X = Ge, Sn, and Pb), which can be prepared by atomic isovalent substitutions of the recently synthesized crystal Ge 4 Se 3 Te. Among them, 2D PbSe possesses a large Seebeck coefficient of ∼1150 μV/K and an ultralow lattice thermal conductivity of ∼0.50 W/mK at room temperature. Theoretical calculations prove that the antiparallel movements of the atoms could lead to the strong optical-acoustic phonon coupling with low values of acoustic group velocities of 0.81−2.03 km/s and large Gruneisen parameters of ∼4, which accordingly greatly suppresses the heat transport ability. Using our calculated transport parameters, large values of the thermoelectric (TE) figure of merit (ZT) of 1.76, 2.32, and 3.95 can be obtained at an effective temperature range (GeSe and SnSe at 700 K and PbSe at 500 K) under p-type doping for 2D GeSe, SnSe, and PbSe, respectively. Interestingly, after checking several series of 2D materials, we find that their lattice thermal conductivities are almost proportional to their values of the lowest optical phonon frequencies. Our work clearly shows the advantages of these novel 2D group-IV selenides as TE materials and may stimulate further experimental and theoretical studies in this field.
Effects of different Y contents (0, 0.3, 0.7, 1.5, 3, 5 and 10 wt.%) on the microstructure, thermal stability and mechanical properties of Mg-3Zn-1Mn (ZM31) alloys were systematically studied. The existence form and action mechanism of Y in the experimental alloys were investigated. The results revealed that with the change of Y content, the main phases of the ZM31-xY alloys changed from Mg7Zn3 phase, I-phase, I + W-phase, W-phase, W + LPSO phase to LPSO phase. When Y content was low (≤1.5%), hot extrusion could break up the residual phases after homogenization to form dispersed fine rare-earth phase particles, and fine second phases would also precipitate in the grain, which could inhibit the grain growth. When Y content was high (≥3%), the experimental alloys were only suitable for high-temperature extrusion due to the formation of the high heat stable rare-earth LPSO phase. In addition, Y could evidently enhance the mechanical properties of the as-extruded ZM31 alloy, of which the ZM31-10Y alloy had the best mechanical properties, that is, the tensile and yield strengths are 403 MPa and 342 MPa. The high strengths of the alloys were mainly determined by fine grain strengthening, rare-earth phase strengthening and dispersion strengthening of fine α-Mn particles.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.