In a preceding project, functional forms for “short” Helmholtz energy equations of state for typical nonpolar and weakly polar fluids and for typical polar fluids were developed using simultaneous optimization. In this work, the coefficients of these short forms for the equations of state have been fitted for the fluids acetone, carbon monoxide, carbonyl sulfide, decane, hydrogen sulfide, 2-methylbutane (isopentane), 2,2-dimethylpropane (neopentane), 2-methylpentane (isohexane), krypton, nitrous oxide, nonane, sulfur dioxide, toluene, xenon, hexafluoroethane (R-116), 1,1-dichloro-1-fluoroethane (R-141b), 1-chloro-1,1-difluoroethane (R-142b), octafluoropropane (R-218), 1,1,1,3,3-pentafluoropropane (R-245fa), and fluoromethane (R-41). The 12 coefficients of the equations of state were fitted to substance specific data sets. The results show that simultaneously optimized functional forms can be applied to other fluids out of the same class of fluids for which they were optimized without significant loss of a...

Short Fundamental Equations of State for 20 Industrial Fluids

Using first-principles calculations, we systematically study the elastic stiffness constants, mechanical properties, elastic wave velocities, Debye temperature, melting temperature, and specific heat of several thermodynamically stable crystal structures of ${\mathrm{Bi}}_{x}{\mathrm{Sb}}_{1\ensuremath{-}x}$ ($0lxl1$) binaries, which are of great interest due to their numerous inherent rich properties, such as thermoelectricity, thermomagnetic cooling, strong spin-orbit coupling (SOC) effects, and topological features in the electronic band structure. We analyze the bulk modulus ($B$), Young's modulus ($E$), shear modulus ($G$), $B/G$ ratio, and Poisson's ratio ($\ensuremath{\nu}$) as a function of the Bi concentration in ${\mathrm{Bi}}_{x}{\mathrm{Sb}}_{1\ensuremath{-}x}$. The effect of SOC on the above-mentioned properties is further investigated. In general, we observe that the SOC effects cause elastic softening in most of the studied structures. Three monoclinic structures of Bi-Sb binaries are found to exhibit significantly large auxetic behavior due to the hingelike geometric structure of bonds. The Debye temperature and the magnitude of the elastic wave velocities monotonically increase with increasing Sb concentration. However, anomalies were observed at very low Sb concentration. We also discuss the specific-heat capacity versus temperature data for all studied binaries. Our theoretical results are in excellent agreement with the existing experimental and theoretical data. The comprehensive understanding of the material properties such as hardness, mechanical strength, melting temperature, propagation of the elastic waves, auxeticity, and heat capacity is vital for practical applications of the studied binaries.

Elastic, mechanical, and thermodynamic properties of Bi-Sb binaries: Effect of spin-orbit coupling

We present the synthesis of Bi1–xSbx nanowires with controlled composition between x = 0.05 and x = 0.40 over a wide range of diameters (20–100 nm) interesting for the investigation of the enhancement of thermoelectric efficiency via quantum size effects. We find that the relative concentration of Bi and Sb ions in the electrolyte, together with the deposition potential, determines the resulting nanowire composition. Morphology and composition were analyzed using X-ray diffraction, electron microscopy, and energy dispersive X-ray analysis. Two different templates were fabricated to enable the synthesis of nanowires with smooth and rough contour.

Electrochemical synthesis of Bi1−xSbx nanowires with simultaneous control on size, composition, and surface roughness

Using first principles calculations, we systematically study the elastic stiffness constants, mechanical properties, elastic wave velocities, Debye temperature, melting temperature, and specific heat of several thermodynamically stable crystal structures of Bi$_{x}$Sb$_{1-x}$ ($0 < x < 1$) binaries, which are of great interest due to their numerous inherent rich properties, such as thermoelectricity, thermomagnetic cooling, strong spin-orbit coupling (SOC) effects, and topological features in the electronic bandstructure. We analyze the bulk modulus ($B$), Young's modulus ($E$), shear modulus ($G$), $B/G$ ratio, and Poisson's ratio ($\nu$) as a function of the Bi concentration in Bi$_{x}$Sb$_{1-x}$. The effect of SOC on above mentioned properties is further investigated. In general, we observe that the SOC effects cause elastic softening in most of the studied structures. Three monoclinic structures of Bi-Sb binaries are found to exhibit significantly large auxeticity. The Debye temperature and the magnitude of the elastic wave velocities monotonically decrease with increasing Bi-concentration. We also discuss the specific heat capacity versus temperature data for all studied binaries. Our theoretical results are in excellent agreement with the existing experimental and theoretical data. The comprehensive understanding of the material properties such as hardness, mechanical strength, melting temperature, propagation of the elastic waves, auxeticity, and heat capacity is vital for practical applications of the studied binaries.

The elastic, mechanical and thermodynamic properties of Bi-Sb binaries: Effect of spin-orbit coupling

Semi-conducting alloys BixSb1−x have emerged as a potential candidate for topological insulators and are well known for their novel thermoelectric properties. In this work, we present a systematic study of the low-energy phases of 35 different compositions of BixSb1−x (0 < x < 1) at zero temperature and zero pressure. We explore the potential energy surface of BixSb1−x as a function of Sb concentration by using the ab initio minima hopping structural search method. Even though Bi and Sb crystallize in the same Rm space group, our calculations indicate that BixSb1−x alloys can have several other thermodynamically stable crystal structures. In addition to the configurations on the convex hull, we find a large number of metastable structures which are dynamically stable. The electronic band structure calculations of several stable phases reveal the presence of strong spin–orbit interaction leading to the Rashba–Dresselhaus spin-splitting of bands which is of great interest for spintronics applications. We also find an orthorhombic structure of BiSb in the Imm2 space group which exhibits signatures of type-II Weyl semimetal. Additionally, we have studied the thermoelectric properties of the selected structures. Regarding thermoelectric properties, we find that the compositions which crystallize in the rhombohedral structure exhibit values of the Seebeck coefficient and the power factor similar to that of Bi2Te3 at room temperature, while the theoretical maximum figure of merit (ZeT) is smaller than that of Bi2Te3. We observe enhancement in the thermopower with the increase in the strength of the Rashba–Dresselhaus spin-splitting effect.

J. P. Dismukes

Papers

Lattice parameter and density in bismuth-antimony alloys