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Yu, Guodong

Publications and source records attributed to Yu, Guodong.

4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Origins of ultralow thermal conductivity in 1-2-1-4 quaternary selenides

Engineering the thermal properties in solids is important for both fundamental physics (e.g. electric and phonon transport) and device applications (e.g. thermal insulating coating, thermoelectrics). In this paper, we report low thermal transport properties of four selenide compounds ( BaAb 2 SnSe 4 , BaCu 2 GeSe 4 , BaCu 2 SnSe 4 and SrCu 2 GeSe 4 ) with experimentally-measured thermal conductivity as low as 0.31 ± 0.03 W m -1 K -1 at 673 K for BaAg 2 SnSe 4 . Density functional theory calculations predict κ < 0.3 W m -1 K -1 for BaAg 2 SnSe 4 due to scattering from weakly-bonded Ag–Ag dimers. Lastly, defect calculations suggest that achieving high hole doping levels in these materials could be challenging due to monovalent (e.g., Ag) interstitials acting as hole killers, resulting in overall low electrical conductivity in these compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2017

A computational assessment of the electronic, thermoelectric, and defect properties of bournonite (CuPbSbS 3 ) and related substitutions

Bournonite (CuPbSbS 3 ) is an earth-abundant mineral with potential thermoelectric applications. This material has a complex crystal structure (space group Pmn2 1 #31) and has previously been measured to exhibit a very low thermal conductivity (κ < 1 W m -1 K -1 at T ≥ 300 K). In this study, we employ high-throughput density functional theory calculations to investigate how the properties of the bournonite crystal structure change with elemental substitutions. Specifically, we compute the stability and electronic properties of 320 structures generated via substitutions {Na-K-Cu-Ag}{Si-Ge-Sn-Pb}{N-P-As-Sb-Bi}{O-S-Se-Te} in the ABCD 3 formula. We perform two types of transport calculations: the BoltzTraP model, which has been extensively tested, and a newer AMSET model that we have developed and which incorporates scattering effects. We discuss the differences in the model results, finding qualitative agreement except in the case of degenerate bands. Based on our calculations, we identify p-type CuPbSbSe 3 , CuSnSbSe 3 and CuPbAsSe 3 as potentially promising materials for further investigation. We additionally calculate the defect properties, finding that n-type behavior in bournonite and the selected materials is highly unlikely, and p-type behavior might be enhanced by employing Sb-poor synthesis conditions to prevent the formation of Sb Pb defects. Finally, we discuss the origins of various trends with chemical substitution, including the possible role of stereochemically active lone pair effects in stabilizing the bournonite structure and the effect of cation and anion selection on the calculated band gap.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Surface magnetism of the carbon foam: An ab-initio theoretical study

By means of ab-initio calculations, we study the surface magnetism of carbon foam, a carbon allotrope constructed by both the sp{sup 2} and sp{sup 3} hybridized carbon atoms. It is found that the sp{sup 3}-terminated surface and sp{sup 2}-terminated surface with hydrogen saturation (sp{sup 2}H) have the antiferromagnetic and ferromagnetic ground states, respectively. And the corresponding phase transition temperatures of these two surfaces are estimated to exceed 100 K. In addition, the magnetic moment of the sp{sup 2}H surface can be effectively modulated by strain. More interestingly, at the level of generalized gradient approximation, as the lattice are stretched, a bulk bandgap will open. And in such a bandgap, the sp{sup 2}H surface states can form spin polarized Dirac cones at K(K′) point. Thus, in the vicinity of the Fermi level, only the electron with a specific spin behaves like a Dirac Fermion.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗