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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Large Nernst Effect and Thermodynamics Properties in Weyl Antiferromagnet

The noncollinear antiferromagnet Mn3Sn exhibits a large anomalous Hall effect (AHE) driven by a large Berry curvature despite the vanishingly small magnetization. Theoretically, the large Berry curvature in antiferromagnets is predicted to be induced by the time-reversal breaking Weyl state in momentum space. Here, we comprehensively study the thermal conductivity, specific heat, thermoelectric power S(T), and thermomagnetic power S ji (T) in single crystals of Mn 3 Sn. Mn 3 Sn exhibited a large spontaneous anomalous Nernst effect (ANE) at room temperature; in particular, the signal magnitude of Mn 3 Sn exceeded 0.6 µV/K, which is comparable to that of ordinary ferromagnets. The large ANE results from the magnetic Weyl states near the Fermi level E F and likely shares its origin with the AHE. Moreover, the possibility of Nernst-type thermoelectric modules was evaluated by analyzing the basic thermal and electric physical properties.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1972

The thermodynamic properties of nitrogen from 65 to 2000 K with pressures to 10,000 atmospheres

An equation of state is presented for liquid and gaseous nitrogen for temperatures from 65 degrees K to 2000 degrees K and pressures to 10,000 atmospheres. All the pressure-density-temperature data available from published literature have been corrected and applied to bring experimental temperatures into accord with the International Practical Temperature Scale of 1968. The coefficients of the equation of state were determined by a weighted least squares fit to selected published pressure-density-temperature data. The methods of weighting the various data for simultaneous fitting are presented and discussed.

Jacobsen, R. T.↗
NASA NTRS1972

Solid-gas phase equilibria and thermodynamic properties of cadmium selenide.

Accurate vapor pressures are determined through direct weight loss measurements using the Knudsen effusion technique. The experimental data are evaluated by establishing the mode of vaporization and determining the heat capacity of cadmium selenide at elevated temperatures. Additional information is obtained through a second- and third-law evaluation of data, namely, the heat of formation and the absolute entropy of cadmium selenide. A preferential loss of selenium during the initial heating of CdSe is observed, which leads to a deviation in stoichiometry.

Sigai, A. G.↗
NASA NTRS1972

Lattice model calculation of elastic and thermodynamic properties at high pressure and temperature

The elastic constants and the entire frequency spectrum were calculated up to high pressure for the alkali halides in the NaCl lattice, based on an assumed functional form of the inter-atomic potential. The quasiharmonic approximation is used to calculate the vibrational contribution to the pressure and the elastic constants at arbitrary temperature. By explicitly accounting for the effect of thermal and zero point motion, the adjustable parameters in the potential are determined to a high degree of accuracy from the elastic constants and their pressure derivatives measured at zero pressure. The calculated Gruneisen parameter, the elastic constants and their pressure derivatives are in good agreement with experimental results up to about 600 K. The model predicts that for some alkali halides the Grunesen parameter may decrease monotonically with pressure, while for others it may increase with pressure, after an initial decrease.

Demarest, H. H., Jr.↗
NASA NTRS1974

Free energies of formation of WC and WzC and the thermodynamic properties of carbon in solid tungsten

The activity of carbon in the two-phase regions - W + WC and W + W2C was obtained from the carbon content of iron rods equilibrated with mixtures of metal plus carbide powders. From this activity data the standard free energies of formation of WC and W2C were calculated. The temperature of the invariant reaction W2C = W + WC was fixed at 1570 + or - 5K. Using available solubility data for C in solid W, the partial molar free energy of C in the dilute solid solution was also calculated. The heat of solution of C in W, and the excess entropy for the interstitial solid solution, were computed, assuming that the carbon atoms reside in the octahedral interstices of bcc W.

Gupta, D. K.↗