Materials Literature
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We report an ab initio calculation of the binding energies and the nature of the excitonic states in the near-gap absorption spectrum of a real solid, ${\mathrm{Li}}_{2}$O. We calculate the ground-state properties using density-functional theory together with soft pseudopotentials. Applying Hedin's GW approximation fo…
Structural changes of tussah (Antheraea pernyi) silk fibroin films induced by heat treatment were studied as a function of the treatment temperature in the range 200–250°C. The DSC curve of tussah films with α-helix molecular conformation displayed characteristic endo and exo peaks at 216 and 226°C, respectively. Thes…
The effect of Fe doping (<20%) on the Mn site in the ferromagnetic (x=0.37) and the antiferromagnetic (x=0.53) phases of La1−xCaxMnO3 has been studied. Upon doping, no appreciable structure changes have been found in either series. However, conduction and ferromagnetism have been consistently suppressed by Fe d…
A probable heterodiamond ${\mathrm{BC}}_{2}$N structure that can be obtained from compression of graphitic ${\mathrm{BC}}_{2}$N at low temperature is proposed using first-principles calculations. The structure consists of a rhombohedral atomic arrangement and has a large bulk modulus comparable to that of diamond as w…
Permanent magnets play a vital role in modern society as a component in a wide range of devices utilized by many industries and consumers. In 1995, the world production of permanent magnets was estimated to be valued at $3.6 billion and growing at an annual rate of 12%. Bonded permanent magnets are the fastest growing…
Within the framework of a partial-density approach, the confinement of vibrations in spherical Si nanocrystals is studied and the Raman frequency shifts of Si spheres with different sizes are derived based on the Raman spectra obtained by a bond-polarizability model. The results obtained by the bond-polarizability mod…
The attributes of electron field emission from disordered matrix arrays of carbon nanotubes are studied and found to be quite reproducible in spite of the disorder, density, and quality variations from sample to sample. At low applied electric fields, the electron field emission current-voltage characteristics qualita…
In the substitutionally disordered narrow-gap semiconductor Pb_{1-x}Ge_xTe, a finite-temperature cubic-rhombohedral transition appears above a critical concentration $x \approx 0.005$. As a first step towards a first-principles investigation of this transition in the disordered system, a (hypothetical) ordered cubic P…
We apply ab initio quantum chemical methods to calculate correlation effects on cohesive properties of NiO, thereby extending a recently proposed scheme to transition-metal oxides with partially filled d bands. We obtain good agreement with experiment for the cohesive energy and show that the deviation of the lattice…
The bare and hydrogen-covered diamond (100) surfaces were investigated through pseudopotential density-functional calculations within the local-density approximation. Different hydrogen coverages, ranging from one to two, were considered. These corresponded to different structures (1\ifmmode\times\else\texttimes\fi{}1…
A “colossal” negative magnetoresistance (CMR) occurs in manganites at a first-order ferromagnetic transition. The Mn4+ and high-spin Mn3+ ions each contain localized t3 configurations; the t3–pπ–t3 superexchange interactions are antiferromagnetic. The orbital degeneracy of localized Mn3+:t3e1, Eg5 configurations is li…
The exciton-phonon coupling strength of PbS nanocrystals that strongly confine both charge carriers is investigated using resonant Raman scattering. The strength of this coupling (Huang-Rhys parameter S\ensuremath{\sim}0.7) is four orders of magnitude greater than that predicted theoretically for the intrinsic states…
Anomalous magnetic properties of organic coated NiFe2O4 nanoparticles have been reported previously (Berkowitz et al.).5 These properties included low magnetization with a large differential susceptibility at high fields and shifted hysteresis loops after field cooling, while Mössbauer spectra indicated that all of th…
The oxidation of liquid-gallium surfaces has been investigated with surface x-ray scattering techniques. By exposing the liquid-metal surface at room temperature to doses on the order of 180 L of oxygen where 1 L=${10}^{\mathrm{\ensuremath{-}}6}$ Torr s, a gallium oxide film with a well-defined thickness of \ensuremat…
The changes in density, wave functions, and self-consistent potentials of solids, in response to small atomic displacements or infinitesimal homogeneous electric fields, are considered in the framework of the density-functional theory. A variational principle for second-order derivatives of the energy provides a basis…
Abstract Mercury is known to be present as a trace component in many natural gas reservoirs. As an environmentally hazardous element, mercury has to be removed from the gas stream, preferably on the production site. This removal causes various problems for the operator. First of all the selection of adequate analytica…
There is a quite serious discrepancy in the literature, in the electron energy range 5 - 10 eV, between the most recent elastic differential cross section (DCS) measurements of Woeste et al and Sullivan et al , particularly for electron scattering angles of less than . This disagreement is reflected in both the shape…
The magnetization of F- and P-type icosahedral Al - Pd - Mn was studied in the temperature region between 2 and 870 K in a magnetic field below 80 kOe. F-type icosahedral phase samples obtained by quenching from 1075 K were transformed to the low-temperature-phase form during the magnetic measurement above 600 K. The…
A novel layer-by-layer cubic growth pathway involving ${\mathrm{C}}_{2}$ dimers is advanced for large titanium carbide clusters based on observation of new magic numbers in the anions. This growth mechanism explains uniquely all the magic numbers in a multicage growth model previously proposed for large metal carbide…
Dielectric spectroscopy up to a frequency of 380 GHz has been performed on the molten salts $[\mathrm{Ca}({\mathrm{NO}}_{3}{)}_{2}{]}_{0.4}[{\mathrm{KNO}}_{3}{]}_{0.6}$ (CKN) and $[\mathrm{Ca}({\mathrm{NO}}_{3}{)}_{2}{]}_{0.4}[{\mathrm{RbNO}}_{3}{]}_{0.6}$ (CRN). For the first time, conclusive results for the transiti…