Materials Literature
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The fundamental issue of ``bands versus bonds'' in metal oxides is addressed through the direct comparison of results from scattered-wave cluster-molecular-orbital and augmented-spherical-wave band-structure calculations for zinc oxide and copper-impurity systems therein. It is shown that there is a close corresponden…
The Bhatia-Thornton and Faber-Ziman partial structure factors (PSF) for liquid ${\mathrm{Al}}_{80}$${\mathrm{Ni}}_{20}$ have been determined by neutron diffraction from samples of different Ni isotopic enrichment. From the comparison with the PSF of the liquid ${\mathrm{Al}}_{80}$[${\mathrm{Mn}}_{\mathit{x}}$(FeCr${)}…
The freezing phase transition in a binary suspension of colloidal hard spheres of diameter ratio α=0.61 was studied by light scattering and scanning electron microscopy. The suspensions consisted of sterically stabilized poly(methyl methacrylate) spheres of diameters about 670 and 407 nm suspended in a near refractive…
The first measurements are reported for the frequency-dependent ac conductivity for the iron bismuthate glassy semiconductors in the frequency range ${10}^{2}$--${10}^{5}$ Hz and in the temperature range 80--450 K. The experimental data have been analyzed with reference to various theoretical models based on quantum-m…
Spin-polarized measurements of the two-dimensional angular correlation of annihilation radiation in NiMnSb are presented. By making use of the inherent partial polarization of the positron beam and the alignment of the magnetic domains with the aid of an external magnetic field, the sum and difference of the spin-depe…
Using a basis set of \ensuremath{\sim}3580 plane waves, we perform ab initio self-consistent calculations of the energy bands and cohesive energy of ${\mathrm{B}}_{12}$${\mathrm{C}}_{3}$. Calculating stresses and forces, both the lattice constants and the positions of the atoms in the unit cell are determined. If trig…
Type-IIA diamond single crystals containing approximately 0.1%, 0.5%, and 1% $^{13}\mathrm{C}$ were synthesized and their thermal diffusivities were measured at room temperature by the thermal-wave-mirage technique. The measured value (18.5 ${\mathrm{cm}}^{2}$/s) of the 0.1% $^{13}\mathrm{C}$ crystal was 50% higher th…
Reports the observed variation of electrical resistivity with thickness of tin oxide films grown by spray pyrolysis. An explanation for the observed variation is also given.
Highly orientated films of the transition metal dichalcogenides 2H-MoS 2 , 2H-WS 2 , 2H-TaS 2 and 3R-NbS 2 have been prepared using a suspension of the powders in water. The layered material is collected at the water/organic interface by shaking the suspension with a water-immiscible organic liquid. The films are spre…
The square-array model with infinite chains of contact is proposed to account for the dependence of electrical properties on frequency and fibre volume fraction in unidirectional carbon-fibre/epoxy-resin composites. The longitudinal AC conductivity, E vector parallel to fibre axis, decreases with increasing frequency…
A method is described whereby ion implantation profiles in amorphous materials may be accurately represented by Pearson frequency distribution curves. The type of Pearson distribution to be used depends upon the implantation conditions but it is shown that the three main types, I, IV and VI, together with the transiti…
Methane plasmas excited at 25 kHz and 13.56 MHz used for a-C:H deposition have been studied by optical emission spectroscopy. At 25 kHz the emitted bands and lines, namely CH (431.4 nm), H (486.1 nm) and H 2 (463.4 nm), have been found to result from dissociative excitation of the CH 4 molecule under electron impact.…
It is shown that, assuming first order kinetics and a frequency factor s(T) given by s(T)=s 0 T a with -2<or=a<or=2, it is impossible to determine the value of a from any combination of thermally stimulated luminescence (TSL) measurements alone, provided E/kT m is greater than about 20 (E is the activation energy, T m…
Traditionally, synthetic polymers have always been designed to be resistant to microbial attack and are usually stabilized with antioxidants, antiozonants, heat stabilizers and UV stabilizers in order to protect them from environmental degradation. The environmental stability of some polymeric materials, such as const…
Oligomers of synthetic polymers are biodegradable, whereas only few polymers are biodegradable. Polyethylene adipate with Mn 3000 and polycaprolactone with Mn 25,000 were completely degraded by Penicillium spp. Aliphatic and alicyclic polyesters, ester type polyurethanes (I), copolyamide-esters (II) and copolyesters (…
This overview is an attempt to briefly cover the history and recent developments in environmentally degradable commodity and specialty polymers and plastics. Degradation pathways are mentioned, polymer types, including blends, are reported and the limitations of current testing protocols raised. The chapter concludes…
Recent work on the synthesis, structure and some properties of macromolecules bearing furan rings is discussed. Two basic sources of monomers are considered, viz. furfural for monomers apt to undergo chain polymerization and hydroxymethylfurfural for monomers suitable for step polymerization. Within the first context,…
Using synchrotron x-ray-scattering measurements on ${\mathrm{NbSe}}_{3}$, we show that the diffuse scattering associated with the ${\mathit{q}}_{1}$ charge-density-wave fluctiations are rods perpendicular to the (a,b) planes reflecting a 2D regime of fluctuations with an in-plane anisotropy ${\ensuremath{\xi}}_{\mathi…
Large second hyperpolarizabilities, 〈γxxxx〉, have been measured in solutions of two recently prepared organic polymer superlattices. These compounds have period aromatic and quinoidal structures and differ from each other by a side group substituent. The values observed are 1.6×10−29 esu for the parent copolymer and 3…
Infinitely many lines of zero thickness may be adsorbed onto a plane without overlap, and it is shown that the number of lines adsorbed should scale as 1 3/, where is the number of adsorption trials per unit area of surface. This is confirmed by numerical simulation. The adsorption of ellipses with major and minor axe…