Analytic binary alloy volume-concentration relations and the deviation from Zen`s law

Alloys expand or contract as concentrations change, and the resulting relationship between atomic volume and alloy content is an important property of the solid. While a well-known approximation posits that the atomic volume varies linearly with concentration (Zen`s law), the actual variation is more complicated. Here we use an apparent size of the solute (solvent) atom and the elasticity to derive explicit analytical expressions for the atomic volume of binary solid alloys. Two approximations, continuum and terminal, are proposed. Deviations from Zen`s law are studied for 22 binary alloy systems

A Steinberg-Guinan model for High-Pressure Carbon, Diamond Phase

Since the carbon, diamond phase has such a high yield strength, dynamic simulations must account for strength even for strong shock waves ({approx} 3 Mbar). We have determined an initial parametrization of two strength models: Steinberg-Guinan (SG) and a modified or improved SG, that captures the high pressure dependence of the calculated shear modulus up to 10 Mbar. The models are based upon available experimental data and on calculated elastic moduli using robust density functional theory. Additionally, we have evaluated these models using hydrodynamic simulations of planar shocks experiments

Elastic constants and volume changes associated with two high-pressure rhombohedral phase transformations in vanadium

We present results from ab initio calculations of the mechanical properties of the rhombohedral phase (beta) of vanadium metal reported in recent experiments, and other predicted high-pressure phases (gamma and bcc), focusing on properties relevant to dynamic experiments. We find that the volume change associated with these transitions is small: no more than 0.15% (for beta - gamma). Calculations of the single crystal and polycrystal elastic moduli (stress-strain coefficients) reveal a remarkably small discontinuity in the shear modulus and other elastic properties across the phase transitions even at zero temperature where the transitions are first order.Comment: 6 pages, 3 figure

Proper Orthogonal Decomposition Methods for the Analysis of Real-Time Data: Exploring Peak Clustering in a Secondhand Smoke Exposure Intervention

This work explores a method for classifying peaks appearing within a data-intensive time-series. We summarize a case study from a clinical trial aimed at reducing secondhand smoke exposure via the installation of air particle monitors in households. Proper orthogonal decomposition (POD) in conjunction with a k-means clustering algorithm assigns each data peak to one of two clusters. Aversive feedback from the monitors increased the proportion of short-duration, attenuated peaks from 38.8% to 96.6%. For each cluster, a distribution of parameters from a physics-based model of airborne particles is estimated. Peaks generated from these distributions are correctly identified by POD/clustering with \u3e60% accuracy

Theoretical confirmation of a high-pressure rhombohedral phase in vanadium metal

Recent diamond-anvil-cell (DAC) experiments revealed a new phase in vanadium metal at high pressure. Here we present results from first-principles electronic-structure calculations confirming the existence of such phase. The new phase is due to a rhombohedral distortion of the body-centered-cubic (bcc) ambient-pressure phase. The calculated transition pressure of 0.84 Mbar and density compare favorably with the measured data. Interestingly, a re-entrant bcc phase is discovered at an ultra high pressure, close to the limit of DAC experimental capabilities, of about 2.8 Mbar. We show, extending prior work, that the phase transitions in vanadium are driven by subtle electronic-structure effects

Electronic effects at interfaces in Cu - Cr, Mo, Ta, Re Multilayers

In this study we characterize electronic effects in short-period ({approx}20 {angstrom}) metallic multilayer films in which 40% of the atoms are at an interface using near-edge (L{sub 3,2}) x-ray absorption. This study investigates Cu/TM where TM = Cr, MO, W, Ta, Re. These immiscible elemental pairs are ideal to study as they form no compounds and exhibit terminal solid solubility. An interest in the charge transfer between elements in alloys and compounds has led to studies using x-ray absorption as described above. Near edge x-ray absorption fine structure (NEXAFS), a technique used for analyzing x-ray absorption near the absorption edge of the element, is especially suited to study the amount of unoccupied states in the conduction band of a metal. The d-metals spectra show large peaks at the absorption edges called ''white lines.'' These are due to the unoccupied d-states just above the Fermi level in these metals. A study of the white lines in the 3d metals show that as the d-band is increasingly occupied the white lines decrease in intensity. Starting with Ti (3d{sup 2} 4s{sup 2}), which has an almost empty d-band and shows strong white lines, the white-line intensities decrease across the Periodic Chart to Cu (3d{sup 10} 4s{sup 1}), which has a full d-band and no white lines. Systematic measurement of the L{sub 3,2} absorption spectra of bulk elemental Cu and Cu in the Cu/TM multilayers enabled measurement of the charge transfer. NEXAFS on metallic multilayers has received less attention than alloys because of the difficulty in synthesizing multilayers with controllability up to the monolayer level and because there is little difference between the signal from the bulk and from longer period (> 30 {angstrom}) multilayers. For high-quality short period multilayers, however, the difference is clear. This is highlighted in a study of short period Co/Cu multilayers, where the electronic density of states of Cu in Cu/Co greatly differed from that of bulk Cu. The difference was attributed to both charge transfer and band structure changes of the interface atoms. Short period Cu/Fe was the subject of another NEXAFS study, where the signal from a periodic Cu(3 {angstrom})/Fe(10 {angstrom}) multilayer was compared with that of a periodic Cu(10 {angstrom})/Fe(3 {angstrom}) multilayer. The difference was attributed to the different structure of the Cu in each sample. Cu was BCC in one and was FCC in the other

Electronic and structural properties of vacancies on and below the GaP(110) surface

We have performed total-energy density-functional calculations using first-principles pseudopotentials to determine the atomic and electronic structure of neutral surface and subsurface vacancies at the GaP(110) surface. The cation as well as the anion surface vacancy show a pronounced inward relaxation of the three nearest neighbor atoms towards the vacancy while the surface point-group symmetry is maintained. For both types of vacancies we find a singly occupied level at mid gap. Subsurface vacancies below the second layer display essentially the same properties as bulk defects. Our results for vacancies in the second layer show features not observed for either surface or bulk vacancies: Large relaxations occur and both defects are unstable against the formation of antisite vacancy complexes. Simulating scanning tunneling microscope pictures of the different vacancies we find excellent agreement with experimental data for the surface vacancies and predict the signatures of subsurface vacancies.Comment: 10 pages, 6 figures, Submitted to Phys. Rev. B, Other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm