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The thermal equation of state (TEOS) for solids is a mathematic model among pressure, temperature and density, and is essential for geophysical, geochemical, and other high pressure–temperature (high P–T) researches. However, in the last few decades, there has been a growing concern about the accuracy of the pressure scales of the calibrants, and efforts have been made to improve it by either introducing a reference standard or building new thermal pressure models. The existing thermal equation of state, P(V, T) = P(V, T0) + Pth(V, T), consists of an isothermal compression and an isochoric heating, while the thermal pressure is the pressure change in the isochoric heating. In this paper, we demonstrate that, for solids in a soft pressure medium in a diamond anvil cell, the thermal pressure can neither be determined from a single heating process, nor from the thermal pressure of its calibrant. To avoid the thermal pressure, we propose to replace the thermal pressure with a well-known thermal expansion model, and integrate it with the isothermal compression model to yields a Birch–Murnaghan-expansion TEOS model, called VPT TEOS. The predicted pressure of MgO and Au at ambient pressure from Birch–Murnaghan-expansion VPT TEOS model matches the experimental pressure of zero (0) GPa very well, while the pressure prediction from the approximated Anderson PVT TEOS exhibit a big deviation and a wrong trend.

In this work, the performance of the carbon doped compositionally complex alloy (CCA) MoNbTaW was studied under ambient and high pressure and high temperature conditions. TaC and NbC carbides were formed when a large concentration of carbon was introduced while synthesizing the MoNbTaW alloy. Both FCC carbides and BCC CCA phases were detected in the sample compound at room temperature, in which the BCC phase was believed to have only refractory elements MoNbTaW while FCC carbide came from TaC and NbC. Carbides in the carbon doped MoNbTaW alloy were very stable since no phase transition was obtained even under 3.1 GPa and 870 °C by employing the resistor-heating diamond anvil cell (DAC) synchrotron X-ray diffraction technique. Via in situ examination, this study confirms the stability of carbides and MoNbTaW in the carbon doped CCA even under high pressure and high temperature.

Hardness is an essential property in the design of refractory high entropy alloys (RHEAs). This study shows how a neural network (NN) model can be used to predict the hardness of a RHEA, for the first time. We predicted the hardness of several alloys, including the novel C0.1Cr3Mo11.9Nb20Re15Ta30W20 using the NN model. The hardness predicted from the NN model was consistent with the available experimental results. The NN model prediction of C0.1Cr3Mo11.9Nb20Re15Ta30W20 was verified by experimentally synthesizing and investigating its microstructure properties and hardness. This model provides an alternative route to determine the Vickers hardness of RHEAs.

Refractory high-entropy alloys (RHEAs) Al20+xCr20-xMo20-yTi20V20+y ((x, y) = (0, 0), (0, 10), and (10, 15)) were computationally studied to obtain a low density and a better mechanical property. The density functional theory (DFT) method was employed to compute the structural and mechanical properties of the alloys, based on a large unit cell model of randomly distributed elements. Debye&ndash, Gr&uuml, neisen theory was used to study the thermal properties of Al20+xCr20-xMo20-yTi20V20+y. The phase diagram calculation shows that all three RHEAs have a single body-centered cubic (BCC) structure at high temperatures ranging from 1000 K to 2000 K. The RHEA Al30Cr10Mo5Ti20V35 has shown a low density of 5.16 g/cm3 and a hardness of 5.56 GPa. The studied RHEAs could be potential candidates for high-temperature application materials where high hardness, ductility, and low density are required.

The excellent mechanical properties of high-entropy alloys (HEAs) make them promising materials for advances in science and technology. However, the underlying mechanism of plastic deformation is not well understood. In situ experiments are urgently required to provide a fundamental understanding of the plastic deformation under high pressure. We performed in situ synchrotron X-ray diffraction (XRD) experiments to study compression deformation behavior of the HEA MoNbTaVW in a radial diamond anvil cell (rDAC). Our results show that the strength and ratio of the stress-to-shear modulus values are ~1.5 and 3 times that of pure tungsten (W), respectively. MoNbTaVW showed plastic deformation above 5 GPa and displayed a much stronger texture. We found that the active dislocation behavior is mainly responsible for the high strength in MoNbTaVW under compression. This unique technique opens a new avenue to investigate the in situ mechanical properties and their mechanism in other types of HEAs.

Discovery of new single-phase high-entropy alloys (HEAs) is important to understand HEA formation mechanisms. The present study reports computational design and experimental validation of a senary HEA, HfNbTaTiVZr, in a body-centered cubic structure. The phase diagrams and thermodynamic properties of this senary system were modeled using the CALPHAD method. Its atomic structure and diffusion constants were studied using ab initio molecular dynamics simulations. The microstructure of the as-cast HfNbTaTiVZr alloy was studied using X-ray diffraction and scanning electron microscopy, and the microsegregation in the as-cast state was found to qualitatively agree with the solidification predictions from CALPHAD. Supported by both simulation and experimental results, the HEA formation rules are discussed.

The design approach and validation of a single phase senary refractory high entropy alloy (HEA) MoNbTaTiVW was presented in the present study. The design approach was to combine phase diagram inspection of available binary and ternary systems and Calculation of Phase Diagrams prediction. Experiments using X-ray diffraction and scanning electron microscopy techniques verified a single phase microstructure in body centred cubic lattice for MoNbTaTiVW. The observed elemental segregation agrees well with the solidification prediction using the Scheil model. The lattice constant, density and microhardness were measured to be 0.3216 nm, 4.954 GPa and 11.70 g cm− 3 respectively. The atomic size difference, the Ω parameter, enthalpy of mixing and entropy of mixing for MoNbTaTiVW HEA are 3.1%, 11.1, − 3.4 kJ mol− 1 and +13.39 J K− 1 mol− 1 respectively.

We proposed and numerically investigated the influence of spatial topology on the infrared frequency region response of chiral metamaterials based on discrete deformed split ring resonators. Compared with the well studied continuous helix, the proposed metamaterials with discrete topology exhibit broad band chiral electromagnetic response. It is shown that the conversion between left and right circular polarization waves for our model is much broader than the continuous helix model. The observed cross-coupling between electric and magnetic fields results from the chiral electric currents on the resonators due to the broken mirror symmetry. The findings are useful for the design of future real three-dimensional chiral metamaterials with tunable optical response.

We have calculated the minimum energies for each of three positionings of the adatom unit cells for Ru(0001)–(3 × 3)–4Kr (high Kr coverage) and for Ru(0001)–(5 × 5)–Kr (low Kr coverage). The differences between the results for the low and high-coverage cases may clarify puzzles posed by the experimental results of Narloch and Menzel. The low-coverage solution converges to a structure having Kr in the top site at a height of 3.09 A above the substrate with the adsorption energy 185 meV. In the high-coverage case, adatom unit cells with a corner Kr at top, fcc hollow, and hcp hollow locations are found to have nearly the same adsorption energy of 175 meV. The height of the corner atom above the substrate is found to be 3.35, 3.54, and 3.50 A for the top, fcc hollow and hcp hollow sites, respectively. These results are explained by demonstrating that there is an enhancement of the substrate electronic density of states at krypton orbital energies in the low-coverage case.

We have performed first principles density functional theory method simulations on electronic structures of B, N, Co, P, and Bi doped C60 solids. Our electronic structure simulations show that boron, phosphorous, and cobalt doped face-centered cubic (FCC) C60 solids have the electronic structures of n-type semiconductors. Nitrogen doped FCC C60 solid has an electronic structure similar to those of a p-type semiconductor. P doped C60 is a potential good candidate in thermoelectric application. For Bi doped C60, a transformation from n-type to p-type semiconductor and gradually to metal, which corresponding to the Bi:C60 dopant ratio at 1:60, 2:60, and 3:60, respectively, can be seen from our electronic density of states (DOS) analysis. There are volume contraction and charge transfer increasing in the 2:60 of Bi doped C60 results compared with those of 1:60 Bi doped C60 case. The charge transfer at a tetrahedral site is as three times larger as that of octahedral site. For the concentration of Bi doped C60 higher than 3:60, the system is expected to be a superconductor.

We have performed quantum chemical calculations for coupled oscillations examining CO adsorbed on Cu(1 1 0) and atomic oxygen on the (1 0 0) diamond face. For CO, we find that our calculations show coupling consistent with a dynamic dipole–dipole interaction. In the case of the adsorbed oxygen atoms the dominant coupling seems to be mechanical. The limits of the semiempirical method SAM1 are tested for consistency and precision. Our model gives accuracy within 10% when compared to experiment and works well with near neighbor adsorbates.

Since the synthesis of the first ones in 2008, iron-based high temperature superconductors have been the subject of many studies. This great interest is partly due to their higher, upper magnetic field, smaller Fermi surface around the Γ point, and a larger coherence length. This work is focused on AxFe2Se2 structural superconductor (FeSe, 11 hierarchy; A = K, Cs) as recently observed. ARPES data show novel, electronic structure and a hole-free Fermi surface which is different from previously observed Fermi surface images. We use ab initio density functional theory method to simulate the electronic structure of the novel superconductor AxFe2Se2. We compare this electronic structure with those of other Fe-based superconductors.

The self-field AC loss of the untwisted (Bi,Pb)-2223 tapes made with different matrices, number of filaments, critical currents and process techniques was measured in the frequency range from 20.8 to 363 Hz at 77 K. The losses of different matrix (Bi,Pb)-2223 tapes under different tensile strain were investigated at 50 Hz, 77 K. We find that: (1) in the case of I m / I c I m / I c >0.4, the eddy current loss must be taken into consideration; (2) above the critical current, the loss, which is shown resistive, is independent of current frequency, and differences in processing have a major impact; (3) below the critical current, the losses, P , increase in proportion with I m / I c with slopes less than 3, which is not in accordance with the Bean model; (4) during the elastic stage the self-field AC losses of AgMn and Ag matrix (Bi,Pb)-2223 tapes do not change, while in yielding stage the unstable relations of AC loss vs. axial tensile strain maybe caused by the serrated curve of stress vs. tensile strain relation, and the losses of both AgMn and Ag matrix tapes increase more in the plastic stage.

We report the optimization of a $4\mathrm{Ar}∕\mathrm{Ag}(111)\text{\ensuremath{-}}(\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{7})R19.1\ifmmode^\circ\else\textdegree\fi{}$ monolayer using first-principles density functional theory. The adsorption energies resulting from our ground-state minimizations are similar for all three anchor sites. A commensurate adsorbate cell is comprised of four argon atoms which settle into three different configurations. We refer to these sites as top, threefold hcp hollow, and threefold fcc hollow sites. Each of these structures has one Ar atom located at one of the base sites of the Ag(111) surface. The remaining three Ar atoms are found near the bridge sites of the silver surface. In both of the hollow site structures, the bridge locations are measurably off of the exact geometric bridge positions while maintaining the $\sqrt{7}R19.1\ifmmode^\circ\else\textdegree\fi{}$ unit cell. Our results show that both the hcp and fcc hollow sites have slightly lower adsorption energies than the top site, by only 1.5 and $4.5\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, respectively (per cell of four Ar atoms). The vertical harmonic vibration frequencies were computed for the top, hcp, and fcc hollow sites. They measured 5.22, 5.01, and $5.21\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, respectively. We studied the possible cause for this high-order commensurate monolayer. We have concluded that neither steric repulsion nor hybridization of the electrons of the Ar atoms is the reason for the commensurability in our model. We propose that the causal mechanism is the Novaco-McTague [Phys. Rev. Lett. 38, 1286 (1977)] theory for orientational epitaxy.

We report a density functional calculation which optimizes a structure of supported Au on titania $\mathrm{Au}∕\mathrm{Ti}{\mathrm{O}}_{3}∕\mathrm{Mo}(112)$. Our computations include two different surface configurations $(1\ifmmode\times\else\texttimes\fi{}1)$ and $(1\ifmmode\times\else\texttimes\fi{}3)$. The results of our study detail the geometric and the electronic structure of these systems. The $(1\ifmmode\times\else\texttimes\fi{}1)$ structure has a ${\mathrm{Au}}^{\ensuremath{\delta}\ensuremath{-}}$ monolayer for its top surface. When the Au coverage is increased, the partial second layer of Au (1/3 ML) causes the titania layer to reconstruct, providing a surface made up of three forms of Au (${\mathrm{Au}}^{\ensuremath{\delta}\ensuremath{-}}$, ${\mathrm{Au}}^{0}$, and ${\mathrm{Au}}^{\ensuremath{\delta}+}$). We have added a vibrational component to our study which permits a possible experimental check on our proposed structures. We calculated the frequencies for a CO molecule when chemisorbed and optimized on these ${\mathrm{Au}}^{\ensuremath{\delta}\ensuremath{-}}$, ${\mathrm{Au}}^{0}$, and ${\mathrm{Au}}^{\ensuremath{\delta}+}∕{\mathrm{Au}}^{0}$ bridge sites. The ${\mathrm{Au}}^{\ensuremath{\delta}+}∕{\mathrm{Au}}^{0}$ bridge site has the largest charge transfer with the adsorbing CO and the CO vibrational frequency is redshifted by $321\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ $(40\phantom{\rule{0.3em}{0ex}}\mathrm{meV})$. We observe that the $2{\ensuremath{\pi}}^{*}$ antibonding level of the CO is above the Fermi level and the electronic density of states shows that the electronic levels reach continuously down passed the Fermi level.

Methane adsorbed on graphite was studied using density-functional theory. The structure was fully optimized with strict energy and force convergence criteria. The methane converged to the preferred adsorption sites giving the vibrational frequencies, the energy of adsorption, charge distributions, and the electronic density of states. Under the two coverages studied ($\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ and $2\sqrt{3}\ifmmode\times\else\texttimes\fi{}2\sqrt{3}$) and a differing number of graphite layers (1--6), the methane molecules favored atop sites on the graphite surface with the hydrogen tripod down. We found the methane carbon $3.21\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ above the graphite carbon and the adsorption energy to be $118\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ for the lower coverage. The independent harmonic oscillator vibrational frequency perpendicular to the surface for the $\mathrm{C}{\mathrm{H}}_{4}$ molecule was computed to be $87\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{-1}$. The graphite surface contracted 5.0% and 4.1% for the first and second layers, respectively, from the spacing relative to their bulk values. To benchmark our frequency calculations, we also used second-order Moller-Plesset theory and the local spin density approximation (LSDA) in GAUSSIAN 03 for the molecule. All of our LDA results are in good agreement with corresponding experiments, while under the generalized gradient approximation approximation we get only qualitatively results.

First principles density functional theory — based (GW) method — was used to simulate the electronic structure of the novel iron-based superconductor K 0.8 Fe 2 Se 2. The calculated band gap of K 0.8 Fe 2 Se 2 at the Γ point is 0.15 eV, which is significantly lower than the 0.61 eV of vacancy free crystal KFe 2 Se 2. The d-orbital of Fe atom is overlapped with the p-orbital of Se atom. Charge density analysis shows strong lattice distortion and vacancy related electric dipole and quadruple near the K vacancy. The reflectivity is anisotropic in three coordinate directions.

Pressed bulk samples of C60 doped with P, Co, Al, and Bi have been investigated for their thermoelectric properties. These samples show extremely low thermal conductivity, typically in the range of 0.1–0.3W∕Km at room temperature. The Seebeck coefficients of Co, Al, and Bi doped C60 solids are in the tens of μV∕K; however, for P doped C60 samples, a very large Seebeck coefficient in the order of 103μV∕K was observed. The value of the Seebeck coefficient seems to depend sensitively on the P concentration and changes sign upon annealing at 100°C. Ab initio density functional theory calculations show that the calculated electronic structures and the activation energies strongly depend on the dopants in C60 solids. The high Seebeck coefficient in studied P doped C60 is due to the system’s unique dopant and concentration.