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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

First-principles study on doping and temperature dependence of thermoelectric property of Bi{sub 2}S{sub 3} thermoelectric material

Graphical abstract: The direction-induced ZT is found. At ZZ direction and n = 1.47 × 10{sup 19} cm{sup −3}, the ZT can reach maximal value, 0.36, which is three times as much as maximal laboratorial value. This result matches well the analysis of electron effective mass. Highlights: ► Electrical transportations of Bi{sub 2}S{sub 3} depend on the concentration and temperature. ► The direction-induced ZT is found. ► At ZZ direction and n = 1.47 × 10{sup 19} cm{sup −3}, the ZT can reach maximal value, 0.36. ► The maximal ZT value is three times as much as maximal laboratorial value. ► By doping and temperature tuning, Bi{sub 2}S{sub 3} is a promising thermoelectric material. - Abstract: The electronic structure and thermoelectric property of Bi{sub 2}S{sub 3} are investigated. The electron and hole effective mass of Bi{sub 2}S{sub 3} is analyzed in detail, from which we find that the thermoelectric transportation varies in different directions in Bi{sub 2}S{sub 3} crystal. Along ac plane the higher figure of merit (ZT) could be achieved. For n-type doped Bi{sub 2}S{sub 3}, the optimal doping concentration is found in the range of (1.0–5.0) × 10{sup 19} cm{sup −3}, in which the maximal ZT reaches 0.21 at 900 K, but along ZZ direction, the maximal ZT reaches 0.36. These findings provide a new understanding of thermoelectricity-dependent structure factors and improving ZT ways. The donor concentration N increases as T increases at one bar of pressure under a suitable chemical potential μ, but above this chemical potential μ, the donor concentration N keeps a constant.

36 MATERIALS SCIENCE↗
DOE OSTI2015

First principles treatment of structural, optical, and thermoelectric properties of Li{sub 7}MnN{sub 4} as electrode for a Li secondary battery

The electronic structure, electronic charge density and linear optical properties of the metallic Li{sub 7}MnN{sub 4} compound, having cubic symmetry, are calculated using the full potential linearized augmented plane wave (FP-LAPW) method. The calculated band structure and density of states using the local density, generalized gradient and Engel–Vosko approximations, depict the metallic nature of the cubic Li{sub 7}MnN{sub 4} compound. The bands crossing the Fermi level in the calculated band structure are mainly from the Mn-d states with small support of N-p states. In addition, the Mn-d states at the Fermi level enhance the density of states, which is very useful for the electronic transport properties. The valence electronic charge density depicts strong covalent bond between Mn and two N atoms and polar covalent bond between Mn and Li atoms. The frequency dependent linear optical properties like real and imaginary part of the dielectric function, optical conductivity, reflectivity and energy loss function are calculated on the basis of the computed band structure. Both intra-band and inter-band transitions contribute to the calculated optical parameters. Using the BoltzTraP code, the thermoelectric properties like electrical and thermal conductivity, Seebeck coefficient, power coefficient and heat capacity of the Li{sub 7}MnN{sub 4} are also calculated as a function of temperature and studied.

36 MATERIALS SCIENCE↗
DOE OSTI2015

First-principles study on the bulk and (1 1 1) surface half-metallicity of KS and RbS in CsCl structure

Graphical abstract: Spin-polarized total and atomic DOS at S-(1 1 1) terminated slab and bulk in CsCl-type RbS. - Highlights: • The half metallic properties of CsCl-type RbS and KS have been studied. • The RbS's and KS's (1 1 1) slabs have been investigated. • Surface energy of RbS's and KS's (1 1 1) slabs are calculated. - Abstract: The electronic and magnetic properties of RbS and KS in CsCl structure have been investigated by using the full-potential local-orbital minimum-basis method. Calculating the relation between the total energies and lattice parameters for RbS and KS, we find out that the equilibrium lattice parameters are 4.02 Å and 3.84 Å for RbS and KS, respectively. According to our calculations in generalized gradient approximation approximation, both RbS and KS are half-metallic ferromagnets with the magnetic moments of 1 μ{sub B} per formula unit, and band gap of 4.287 eV for RbS and 4.395 eV for KS. We also have studied the electronic and magnetic properties of (1 1 1) surfaces of RbS and KS, and have found out that the half-metallicity of their bulk is preserved in all of those surfaces. Finally, through the calculations of formation energy of RbS and KS, it is found that their thin films are stable in the equilibrium conditions, and the Rb-terminated (1 1 1) slab of RbS and the K-terminated (1 1 1) slab of KS are more stable than their S-terminated (1 1 1) slabs. All of the above properties lead the compounds of RbS and KS in CsCl structure to be promising candidates for spintronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2016

First principles study of structural, optoelectronic and thermoelectric properties of Cu{sub 2}CdSnX{sub 4} (X = S, Se, Te) chalcogenides

Highlights: • Copper based quaternary chalcogenides are important for optoelectronic devices. • The WC-GGA shows that the materials are metallic in nature. • The EV-GGA predicts better band gaps compared to WC-GGA. • Absorption peaks are high in the visible and ultraviolet energy regions. • All the semiconductors have figure of merit above 0.70. - Abstract: In this work, structural, electronic, optical and thermoelectric properties of Cu{sub 2}CdSnX{sub 4} (X = S, Se, Te) have been studied through the full potential linearized augmented plane wave method. Calculated ground state lattice parameters are in good agreement with the experimental results. Lattice constant and bulk moduli vary inversely by replacing the anion X from S to Te in Cu{sub 2}CdSnX{sub 4}. The WC-GGA shows that the materials are metallic in nature. The EV-GGA predicts better band gaps compared to WC-GGA. The calculated bandgap values are 1.8, 1.06 and 0.8042 for Cu{sub 2}CdSnX{sub 4}, Cu{sub 2}CdSnX{sub 4}, Cu{sub 2}CdSnX{sub 4} respectively. Cd-d, Sn-s and X-p states contribute significantly in the density of states of the compounds. Absorption peaks and optical conductivity is high in the visible and ultraviolet energy regions. All the semiconductors have figure of merit above 0.70. The optical and thermoelectric properties clearly show that Cu{sub 2}CdSnX{sub 4} are potential candidates in the fields of solar cell and thermoelectric technology.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Phonon thermal transport in 2H, 4H and 6H silicon carbide from first principles

Here, silicon carbide (SiC) is a wide band gap semiconductor with a variety of industrial applications. Among its many useful properties is its high thermal conductivity, which makes it advantageous for thermal management applications. In this paper we present ab initio calculations of the in-plane and cross-plane thermal conductivities, κ in and κ out , of three common hexagonal polytypes of SiC: 2H, 4H and 6H. The phonon Boltzmann transport equation is solved iteratively using as input interatomic force constants determined from density functional theory. Both κ in and κ out decrease with increasing n in nH SiC because of additional low-lying optic phonon branches. These optic branches are characterized by low phonon group velocities, and they increase the phase space for phonon-phonon scattering of acoustic modes. Also, for all n, κ in is found to be larger than κ out in the temperature range considered. At electron concentrations present in experimental samples, scattering of phonons by electrons is shown to be negligible except well below room temperature where it can lead to a significant reduction of the lattice thermal conductivity. This work highlights the power of ab initio approaches in giving quantitative, predictive descriptions of thermal transport in materials. It helps explain the qualitative disagreement that exists among different sets of measured thermal conductivity data and provides information of the relative quality of samples from which measured data was obtained.

36 MATERIALS SCIENCE↗