Materials Literature
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We present a valence effective Hamiltonian (VEH) nonempirical investigation of the electronic properties of metal-free phthalocyanine. The valence one-electron energy levels are related to those of the phthalocyanine components: benzene, pyrrole, and isoindole. From the electronic structure standpoint, phthalocyanine…
Mean electronic resonant wavelength of some single substance liquid crystals obtained by ultraviolet transmission spectrum and by wavelength dependent birefringence agrees very well. Both ground and higher state π→π* electronic transitions are found to make a major contribution to the observed birefringence of those l…
Phase transitions of the linear-chain semiconductor (${\mathrm{NbSe}}_{4}$${)}_{3}$I, which occur successively at ${T}_{c1}$=271 K and ${T}_{c2}$\ensuremath{\simeq}100 K, were studied by Raman scattering and electrical resistivity. The resistivity data showed that the band gap increases below ${T}_{c1}$. It was found…
Constraints for quasi-crystals arising from the energetical stability assumption are obtained. For grid models the constraints are expressed in a simple algebraic form (SI-conditions) and applied to planar tilings. SI-conditions allow only for quadratic irrationalities a + b √D ( a, b and D are rational numbers). n -f…
Optical and electro-optic properties of some highly conjugated nematic liquid crystals (LCs): 4-cyano-4′-n-alkyltolanes (n-CDP) and 4-cyano-4′-n-alkylstilbene (n-CS) were studied at elevated temperature. Results are compared with 4-cyano-4′-n-pentylbiphenyl (5CB). These LCs exhibit large birefringence, small viscoelas…
A monomeric arsinogallane containing a covalent gallium-arsenic bond has been prepared, and its molecular structure has been determined by x-ray crystallography. The compound reacted with tert-butanol at ambient temperature to yield the III-V semiconductor gallium arsenide as a finely divided amorphous solid. During t…
A theoretical model is developed to describe the polarization and depinning of charge-density waves (CDW's) in the inorganic linear-chain compounds which exhibit Fr\"ohlich sliding conduction. Each individual impurity within the crystal is assumed to pin the CDW phase very strongly at the impurity site, and dc CDW mot…
We study the short-time collective and self-diffusion coefficients, the rotational self-diffusion coefficient, and the high frequency effective viscosity of a suspension of spherical Brownian particles. At low volume fraction these transport coefficients are given by integrals of hydrodynamic pair interactions. Using…
A remarkable nonlinearity and a switching effect have been observed for electric transport in a tetrathiafulvalene (TTF)-$p$-chloranil crystal. Experimental evidence indicates that these features are of an intrinsic origin associated with the neutral-ionic transition. A possible mechanism is discussed in terms of fiel…
Infinitely degenerate states at an energy E=0 on a two-dimensional Penrose lattice are investigated in a tight-binding model where atomic orbitals are located at vertices of rhombuses. The states with E=0 are all strictly localized and have amplitudes only on some specific vertices, which are three-edge vertices and s…
The large third-order nonlinear optical properties ${\ensuremath{\gamma}}_{\mathrm{ijkl}}(\ensuremath{-}{\ensuremath{\omega}}_{4};{\ensuremath{\omega}}_{1},{\ensuremath{\omega}}_{2},{\ensuremath{\omega}}_{3})$ observed for conjugated organic linear chains, such as polyenes, are explained by strong electron-correlation…
We have derived a nonlocal theory of thermal conductivity for the case in which the heat is carried by phonons. There is a nonlocal relation between the heat current J(r) and the temperature gradient \ensuremath{\nabla}T(r'). The nonlocal theory is needed whenever the phonon mean free path is long compared to the dist…
Hybrid elements containing optical power with both diffractive (holographic) and refractive components are shown to be useful for obtaining arbitrary or, in special cases, achromatic dispersive characteristics. In one configuration a volume holographic element is coated on the surface of a crown glass lens, and by var…
A new approach for including full-potential terms in a linear-muffin-tin-orbital calculation is presented. The implementation for crystals leads to a method which is at the same time fast and accurate. Calculated elastic constants and phonon frequencies for Si agree well with experiment.
The infrared-absorption spectrum of a-${\mathrm{SiO}}_{2}$ is analyzed in terms of its transverse-optic (TO) and longitudinal-optic (LO) vibrational modes. It is shown that the independent-oscillator model for the a-${\mathrm{SiO}}_{2}$ dielectric function fails to yield a consistent value of mode strength for the opt…
Barium titanate semiconducting ceramics with positive temperature coefficients of resistance (PTCR) which were donor doped with holmium have been studied with respect to the effect of holmium concentration on the conductivity in the range of 0.05 to 0.8 at.%. The transition from conductive to insulating behaviour at r…
The electrodeposition of poly(pyrrole) in the presence of a polyanionic electrolyte (poly(styrenesulphonate), poly(vinylsulphate) or Nafion) leads to the formation of a film of a composite polymer at the surface of the two polymeric structures prevents the anionic dopants from being expelled during the dedoping, conse…
The magnetic properties of AISI 4130 steel after eight heat treatments have been investigated. Properties such as hysteresis loss, coercivity, and initial permeability were found to be closely interrelated. Furthermore, they were each dependent on the hardness of the material. A relationship between the hardness and p…
The magnetic properties of a number of specimens of AISI 1000 series plain carbon steels have been measured as functions of chemical composition, microstructure and heat treatment. The results showed that for a given morphology of the carbides the magnetic properties such as coercivity and permeability varied smoothly…
A microscopic theory for obtaining the polarized Raman spectrum of Fibonacci chains is developed and applied to GaAs-AlAs heterostructures. The results of the theory, without adjustable parameters, are compared with experimental data, and remarkable agreement is attained. The treatment is performed in real space and,…