Materials Literature
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Abstract High-level wastes (HLW) can be incorporated in the crystal lattices of coexisting phases in ceramic waste forms. The properties and performances of ceramic waste forms are largely determined by their phase chemistry, phase assemblage and microstructure. Currently, the best categorized advanced ceramic waste f…
Abstract The title compound 1 , {[Fe(H 2 pztc)(H 2 O) 2 ] · 2 H 2 O} ∞ , has been prepared from pyrazinetetracarboxylic acid (H 4 pztc) and Fe(II) salt in H 2 O. It crystallizes in the monoclinic space group P 2 1 / a with cell parameters a = 13.56(1) Å, b = 7.17(1) Å, c = 6.48(1) Å, β = 101.0(2)°, V = 618.4 Å 3 . The…
Abstract A new, accurate, low‐temperature X‐ray analysis of lithium tetrafluoroberyllate, Li 2 BeF 4 , reveals that the charge density in this crystal is better represented as a superposition of spherical neutral‐atom charge distributions than as a superposition of ionic charges. The two distributions are so similar t…
Photoinduced crystallization is investigated by Raman scattering in Ge${\mathrm{Se}}_{2}$ and Si${\mathrm{Se}}_{2}$ glasses. Crystallization into two different structures is observed according as the incident laser power is above or below the threshold. To interpret it a new stochastic random-network model composed of…
We adopt the view that the structure of disordered systems is itself determined by the formation energy of structural deviations from an ideally bonded network. By developing an equilibrium statistical mechanical model for disorder we predict properties of electronic band tails, defects, defect densities of states, an…
A theory is presented in which much of the structure of spiral galaxies arises from a percolation phase transition that underlies the phenomenon of propagating star formation. According to this view, the appearance of spiral arms is a consequence of the differential rotation of the galaxy and the characteristic diverg…
Abstract The luminescence efficiency of the YAG:Tb phosphor (yttrium aluminium garnet, Y 3 Al 5 O 12 ) has been improved by the application of BaF 2 flux to the firing process.
Transmission-electron microscopy of chiral 4-(2-methylpentylphenyl)-4\ensuremath{'}-hexyloxybenzoate (CE4) quenched from its cholesteric and blue phases (BP) I and III are presented. Images of cholesteric and BP I are consistent with an earlier study of similar compounds. CE4 quenched from its BP III is a spaghettilik…
Nonequilibrium periodic textures are induced by a magnetic field $H$ applied to the aligned uniaxial (negative diamagnetic anisotropy) lyotropic nematic phase of the potassium laurate-decanol-water system. Two cases are studied: a rotating field and a static field. For the rotating field a transient one-dimensional st…
We study the plasma excitations of an array of two-dimensional electron-gas layers arranged in a Fibonacci sequence. The plasmon spectrum is analyzed by a transfer-matrix method. It is shown that the spectrum is always "critical," i.e., it corresponds to neither extended nor localized plasmon states. This property is…
In binary liquid mixtures, the growth of wetting layers can be limited by diffusion. At complete wetting, the distance $l$ between the interfaces bounding the layer is shown to grow as $l(t)\ensuremath{\approx}{A}_{*}{t}^{\ensuremath{\theta}}$ for large times $t$ where ${A}_{*}$ increases near the consolute point. In…
We have reconsidered the problem of the critical layer thickness hc for growth of strained heterolayers on lattice-mismatched substrates, using a new approach which allows us to determine the spatial distribution of stresses in a bi-material assembly and include the effects of a finite size of the sample. The possibil…
The heat capacity C(T) of quenched and annealed samples of bulk As 2 S 3 glasses has been measured in the temperature range 1.5 to 20K, and a far-infrared laser has been used to determine the room-temperature absorption alpha ( nu ) as a function of frequency nu in the range 0.6 to 3 THz (20 to 100 cm -1 ). Both C(T)/…
The authors have evaluated the temperature dependence of the tight-binding transfer integral between neighbouring cation molecules for some representative compounds of the (TMTSF) 2 X and (TMTTF) 2 X families using their recently determined low-temperature and/or high-pressure crystallographic structures. The changes…
The superstructure caused by the charge density wave (CDW) of the nearly commensurate (N. C.) phase in 1TTaS2 is studied in atomic scale by a high resolution electron microscope with image processing system and a selected area electron diffraction method. It is found that the super-structure of the N. C. phase, which…
The three dominant cathodoluminescence bands in amorphous SiO2 with maxima at 1.9, 2.7, and 4.3 cV are identical to bands seen in photoluminescence (PL) spectra of irradiated or oxygen-deficient amorphous SiO2. On the basis of the previous PL work these cathodoluminescence (CL) bands can be attributed to non-bridging…
Bi12GeO20 (BGO) and Bi12SiO20 (BSO) single crystals doped with Al, Ga, P, Pb, Or, Nd, Zn, Fe, and Eu are grown from the melt in good optical quality. The segregation coefficients of the dopants range from 0.1 to 5. The undoped crystals are yellow; Al, Ga, and P bleach the crystals and increase their dark conductivity.…
The nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) of the 181 Ta nuclei have been made on 1 T -TaS 2 at 4.2 K in order to get detailed information on the superlattice structure in the commensurate charge density wave state of this material from a microscopic viewpoint. The NMR ane NQR spectra…
Temperature dependence of the dielectric constant, D – E hysteresis loops and pyroelectric charges in Sr 2 Nb 2 O 7 have been studied in the temperature range from 4.2 K to 300 K. In addition to the well known ferroelectric transition at 1615 K, another ferroelectric phase transition occurs at T 0 ∼100 K. The dielectr…
The effect of high magnetic fields on the electronic structure of some quasi-one-dimensional systems with charge- or spin-density waves is examined. Because of the specific anisotropy of the system, small electron and hole pockets created by the density wave can be destroyed by the presence of a magnetic field. This p…