The lattice thermal conductivity ($\ensuremath{\kappa}$) of the thermoelectric materials, Mg${}_{2}$Si, Mg${}_{2}$Sn, and their alloys, are calculated for bulk and nanowires, without adjustable parameters. We find good agreement with bulk experimental results. For large nanowire diameters, size effects are stronger for the alloy than for the pure compounds. For example, in 200 nm diameter nanowires $\ensuremath{\kappa}$ is lower than its bulk value by 30$%$, 20$%$, and 20$%$ for Mg${}_{2}$Si${}_{0.6}$Sn${}_{0.4}$, Mg${}_{2}$Si, and Mg${}_{2}$Sn, respectively. For nanowires less than 20 nm thick, the relative decrease surpasses 50$%$, and it becomes larger in the pure compounds than in the alloy. At room temperature, $\ensuremath{\kappa}$ of Mg${}_{2}$Si${}_{x}$Sn${}_{1\ensuremath{-}x}$ is less sensitive to nanostructuring size effects than Si${}_{x}$Ge${}_{1\ensuremath{-}x}$, but more sensitive than PbTe${}_{x}$Se${}_{1\ensuremath{-}x}$. This suggests that further improvement of Mg${}_{2}$Si${}_{x}$Sn${}_{1\ensuremath{-}x}$ as a nontoxic thermoelectric may be possible.

https://link.aps.org/accepted/10.1103/PhysRevB.86.174307

Thermal conductivity of bulk and nanowire Mg 2 Si x Sn 1-x alloys from first principles

Atomistic modeling of interfaces and their impact on microstructure and properties

Research advances in magnesium and magnesium alloys worldwide in 2020

The double-edge effect of second-phase particles on the recrystallization behaviour and associated mechanical properties of metallic materials

Thermodynamics is the key component of materials science and engineering. The manifestation of thermodynamics is typically represented by phase diagrams, traditionally for binary and ternary systems. Consequently, the applications of thermodynamics have been rather limited in multicomponent engineering materials. Computational thermodynamics, based on the CALPHAD approach developed in the last few decades, has released the power of thermodynamics and enabled scientists and engineers to make phase stability calculations routinely for technologically important engineering materials. Within the similar time frame, first-principles quantum mechanics technique based on density functional theory has progressed significantly and demonstrated in many cases the accuracy of predicted thermodynamic properties comparable with experimental uncertainties. In this paper, the basics of the CALPHAD modeling and first-principles calculations are presented emphasizing current multiscale and multicomponent capability. Our research results on integrating first-principles calculations and the CALPHAD modeling are discussed with examples on enthalpy of formation at 0 K, thermodynamics at finite temperatures, enthalpy of mixing in binary and ternary substitutional solutions, defect structure and lattice preference, and structure of liquid, super-cooled liquid, and glass.

First-Principles Calculations and CALPHAD Modeling of Thermodynamics

http://www.mmm.psu.edu/HZhang2010_Acta_Al12Mg17.pdf

First-principles calculations of the elastic, phonon and thermodynamic properties of Al12Mg17

First-principles calculations of β″-Mg5Si6/α-Al interfaces

Temperature dependent elastic coefficients of Mg2X (X = Si, Ge, Sn, Pb) compounds from first-principles calculations

Two modes of grain boundary pinning by coherent precipitates

To understand the Invar anomalies, such as negative thermal expansion and spontaneous magnetization, we have applied our recently developed thermodynamic framework for a system with itinerant-electron magnetism to the ordered Fe3Pt. The framework has coherently predicted the finite temperature intermixing between the fully ferromagnetic (FM) configuration and the spin-flipping configurations (SFCs). We have also discovered a tri-critical point at which a high-temperature second-order phase transition, between the fully ordered FM phase and the paramagnetic phase which is disordered due to SFCs, becomes first order at low temperatures.

/pdf/thermodynamic-fluctuations-in-magnetic-states-fe3pt-as-a-2fkzoe9vrq.pdf

Y. Wang

Papers

First-principles calculations of the elastic, phonon and thermodynamic properties of Al12Mg17

First-principles calculations of β″-Mg5Si6/α-Al interfaces

Temperature dependent elastic coefficients of Mg2X (X = Si, Ge, Sn, Pb) compounds from first-principles calculations

Two modes of grain boundary pinning by coherent precipitates

Thermodynamic fluctuations in magnetic states: Fe3Pt as a prototype