Materials Literature
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The phonon dispersion curves of the rutile-structure compounds ${\mathrm{GeO}}_{2}$, ${\mathrm{SnO}}_{2}$, ${\mathrm{NbO}}_{2}$, and ${\mathrm{VO}}_{2}$ have been calculated in the framework of a shell model which had been used previously to reproduce the measured dispersion curves of rutile (${\mathrm{TiO}}_{2}$) rat…
We describe detailed analyses of neutron powder diffraction data on Nd2Fe14B at several temperatures and discuss relationships between the crystal structure and the magnetic properties via comparison with other rare earth-transition metal systems, Nd2Fe17 in particular. Diffraction studies have also been performed on…
A model is presented which gives a unique magnetic-field-induced transition from a two-dimensional open-orbit metal to a semimetal. A magnetic field causes the open-orbit electron motion to become progressively more one dimensional, with an effective density of states proportional to H at low field. This leads to a Fe…
Commercial rare earth metals contain several atomic % oxygen, and intermetallics synthesized using these ingredients deviate markedly from the intended compositions. In this work, high purity rare earths (<20 ppm oxygen by weight) were used. Results for R2Fe14B systems with R = Y, Nd, Sm, or Gd have been previo…
A spin reorientation occurs in Nd2Fe14B starting around Ts= 150 K. We present data on tendencies in spin reorientations in systems (Nd1−xRx)2Fe14B and Nd2Fe14−xAxB where R=different rare earths and A=Co, Al. The insensitivity of Ts to some of these substitutions appears to indicate that Nd alone is responsible for the…
Magnetic domain structures in sintered Fe-Nd-B magnets from several suppliers were studied using the polar Kerr effect. Most grains were multidomain in the thermally demagnetized state. Measurement of average surface domain width in several large grains yielded a domain-wall energy of 25 ergs/cm2 for the Fe14Nd2B prim…
A new approach to Preisach’s model which emphasizes the phenomenological nature of this model and its mathematical generality is discussed. This approach enables the formulation of necessary and sufficient conditions under which actual hysteresis nonlinearities can be represented by Preisach’s model.
Static magnetic measurements have been carried out on single crystals of Nd2Fe14B, Sm2Fe14B, and Y2Fe14B from 4.2 to 590 K. Values of K1 estimated from high field measurements at room temperature are 4.5, −12, and 1.1 MJ/m3 for Nd2Fe14B, Sm2Fe14B, and Y2Fe14B, respectively. Anisotropic behavior of the magnetization ve…
We describe calculations of the evolution of the band gap as a function of geometry in conjugated polymers based on aromatic rings: polyparaphenylene, polypyrrole, polythiophene. Our results demonstrate that the gap decreases as a function of increasing quinoid character of the backbone and is thus not minimal in the…
A new method is described which produces fully dense, well-aligned Nd-Fe-B magnets from rapidly quenched ribbons. Full density is achieved by hot pressing at ∼15 kpsi in argon at 700 °C. A second hot press in a larger die cavity to allow deformation transverse to the press direction (die upsetting) introduces a prefer…
Time-of-flight drift mobility experiments have been carried out on pure and chlorine-doped amorphous selenium films. The temperature and field dependence of the drift mobility of both types of carriers have been investigated and the charge transport mechanism has been critically examined in terms of various shallow-tr…
Time-of-flight drift mobility experiments have been carried out on evaporated films of amorphous (a-)Se 0.995 As 0.005 with chlorine as an additive up to approximately 70 at.ppm; drift mobility has been measured as a function of temperature at various applied fields. It is shown that shallow hole traps at approximatel…
ABSTRACT The deposition of scale in the near-wellbore formation and production string can result in a significant decrease in well capacity. Correctly designed scale inhibitor squeezes can successfully prevent scale deposition and the corresponding productivity declines. However, inadequate knowledge of the chemistry…
ABSTRACT The objectives of the study reported in this paper were to evaluate the thermal stability of commercially available surfactants at typical steam injection temperatures and to investigate the kinetics of the thermal degradation process. Surfactant stability tests were performed under conditions of high tempera…
Abstract Electron energy-loss spectroscopy (e. e. l. s.) performed with an electron microscope can be used to obtain plasmon spectra, near-edge fine structure and extended electron energy-loss fine structure (ex. e. l. f. s.), as well as to do chemical analysis on truly microscopic samples. However, the very strength…
Abstract A number of mineralogical and synthetic precipitates undergo solid to solid phase changes via a solution phase. A review of the literature reveals a lack of both experimental data and a framework for its interpretation. A model is developed, for the case of a polymorphic phase transformation, which involves t…
A simple natural Landau theory of two- or three-component systems is described, which appears to give a region of the phase diagram in which quasicrystalline ordering is the state of lowest free energy. The quasicrystals are stabilized by special geometric relations between the length scales characterizing the compone…
Theories for elasticity and dislocation defects in two-dimensional pentagonal and three-dimensional icosahedral quasicrystals are presented.Received 4 February 1985DOI:https://doi.org/10.1103/PhysRevLett.54.1520©1985 American Physical Society
The crystal structure with icosahedral point-group symmetry and long-range orientational order observed by Shechtman et al. in Mn-Al alloys can be explained as a multiple-q density-wave structure with only one length scale. Its existence and stability can be understood from a simple Landau theory. The diffraction spot…
Influence de la composition du caoutchouc, des systemes vulcanisants, de la teneur en oxyde de zinc, du polyethylene chlorosulfone, des antioxygenes, des coagents