Materials Literature
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A model for the electronic and geometric structure of the non-bridging oxygen defect center in fused silica is presented. The structure of the center is determined by the dynamic Jahn-Teller effect, which appears as a forming of an additional oxygen-oxygen bond between the non-bridging oxygen atom and another oxygen a…
As2(SO4)3 belongs to the monoclinic system, space group P2~/c, with a = 9.389 (3), b = 5.255 (2), c = 19.355 (6) .i, fl = 91.88 (2) °, V = 954.5 A, 3, Z = 4, D,, = 3.00 (5), D x = 3.05 Mg m -~. The structure has been solved at 293 K with 1922 independent reflexions (2 = 0 .7107/ i , 0 < 32 °) and refined to a weighted…
Expressions for the relaxation rates for three-phonon "resonant" processes are obtained for the first time. It is also demonstrated that the contribution of such processes can be as high as 30% of the phonon resistivity of Ge at high temperatures. Because of the different temperature dependence from the nonresonant pr…
Additional transitions which appear in the absorption and luminescence spectra of heavily doped (\ensuremath{\sim} 1 at.%) Li${\mathrm{Ga}}_{5}$${\mathrm{O}}_{8}$:${\mathrm{Cr}}^{3+}$ originate on nearest-neighbor Cr-Cr ion systems. By analyzing these spectra at different temperatures, values are obtained for the exch…
The electron spin resonance and polarized optical absorption spectra of V4+ have been studied in single crystals of ZrSiO4, HfSiO4, ThSiO4, and ThGeO4, each having the zircon structure. The principal values of g and A in ZrSiO4 and HfSiO4 are found to be anomalous and significantly different from those of ThSiO4 and T…
A thermodynamics is introduced for fluids subjected to a constant shear. The theory is based primarily on the results of computer simulations using the technique of homogeneous shear nonequilibrium molecular dynamics applied to a system of 108 Lennard-Jones particles. It is supported qualitatively by the results of se…
A statistical theory of nematic systems has been developed for semiflexible polymers on the basis of a new wormlike model of chain statistics. This wormlike chain model closely represents the short-range statistics of real chains and allows the evaluation of the orientation-dependent configurational partition function…
From sets of adsorption isotherms, critical temperatures of two-dimensional condensation have been determined for the first monolayer of Ar, Kr, or Xe adsorbed on a number of lamellar dihalides. Once properly scaled by the critical temperature of the bulk adsorbate, their value appears to be strikingly correlated to t…
Crystal field parameters (Bkq) were obtained for the REOBr:Eu3+ series (RE = Y, La, Gd) and LaOI:Eu3+ from the analysis of fluorescence spectra. The sets of five nonzero Bkq parameters for the C4v symmetry reproduce the experimental 7FJ Stark level schemes within a few cm−1. The Racah (E0–3) and spin–orbit (ζ) paramet…
Electronic energy-band calculations have been performed for the KMg${\mathrm{F}}_{3}$ crystal by using the method of linear combinations of atomic orbitals with a self-consistent-field procedure. The basis set consists of 124 Bloch sums formed by atomic wave functions and single Gaussians. The wave functions of the va…
The dynamic behavior of atoms in bulk amorphous silica SiO2 has been investigated by using the molecular dynamics computer simulation technique to generate the frequency spectrum. A modified Born–Mayer–Huggins equation was used as the interatomic potential function. Due to the covalency of the Si–O bond, the ability o…
The lattice thermal conductivity of superlattices is shown to depend on a new kind of umklapp scattering process, called a mini-umklapp, associated with the mini-Brillouin zone of the superlattice. Expressions for three-phonon mini-umklapp-scattering matrix elements are obtained for superlattices consisting of lattice…
TiO2 varistors with low resistivity were developed to operate at low voltages and have a reasonably high nonlinearity index. The varistor properties of TiO2 ceramics are due to two different groups of dopants. Pentavalent cation dopants are used to decrease the TiO2 lattice resistivity to ≃10–100 Ω cm at 25°C. Divalen…
The complex dielectric constant of liquid water was measured at 9.61 GHz down to −18 °C by means of a two resonant cavities apparatus. The static dielectric constant of bulk samples was also measured at 27.5 MHz down to −16.5 °C using a resonant circuit technique. From the analysis of the experimental results it follo…
The first-order Raman spectra of $3C$-SiC have been measured as a function of hydrostatic pressure up to 22.5 GPa in a diamond anvil cell. The mode-Gr\"uneisen parameters of the LO and TO phonons at $\ensuremath{\Gamma}$ were determined. We observed an increase of the LO-TO splitting with pressure from which an increa…
We have observed fluorescence line narrowing in the LO-phonon-assisted intrinsic exciton emission of $\mathrm{Cd}{\mathrm{S}}_{x}{\mathrm{Se}}_{1\ensuremath{-}x}$, selectively excited over a range of energies below a critical energy ${E}_{\mathrm{em}}$, on the low-energy side of the exciton absorption line. The sharp…
We have calculated the electronic structure of three-dimensional graphite using the modified first-principles Korringa-Kohn-Rostoker technique developed for and applied to the intercalation compound Li${\mathrm{C}}_{6}$. Whereas previous calculations of the electronic band structure of graphite provide explanations ei…
Of the relaxed, graphitic, buckled, and $\ensuremath{\pi}$-bonded-chain-type models for the diamond (111)-(2 \ifmmode\times\else\texttimes\fi{} 1) surface, only the chain model appears to account for the measured surface-band dispersion. The interaction of dangling orbitals which determines the dispersion is large in…
On the basis of both theoretical and experimental studies, it has been suggested that the low-energy charge-excitations introduced into polyacetylene by light doping are charged solitons. However, these solitons are normally bound to oppositely charged impurities so that soliton conduction is inefficient at room tempe…
We investigate diffusion-controlled processes, where the reacting groups (A and B) are attached to long, flexible, macromolecules in melts or in concentrated solutions. We first give a general discussion of the rate constants, and are led to distinguish two fundamental types of behavior, depending on the rms displacem…