Materials Literature
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The fluorescent brightener, Calcofluor White ST, prevents the in vivo assembly of crystalline cellulose microfibrils and ribbons by Acetobacter xylinum. In the presence of more than 0.01 percent Calcofluor, Acetobacter continues to synthesize high-molecular-weight beta-1,4 glucans. X-ray crystallography shows that the…
X-ray diffraction patterns from fibres generally contain a few closely overlapping peaks, each broadened by the contributions of crystallite size, crystallite-size distribution, and lattice distortion. In order to achieve complete characterisation of a fibre by X-ray methods, it is first necessary to separate the indi…
Abstract This paper is a review of x-ray diffraction work in the authors' laboratory to refine the structures of cellulose I and II, and α- and β-chitin, concentrating on the methods used to select between alternate models. Cellulose I is shown to consist of an array of parallel chains, and this conclusion is supporte…
Studies of the anomalous Hall hysteresis loop in the vicinity of Tcomp are carried out to explain whether or not it is caused by the composition gradient across the thickness in amorphous flash evaporated HoCo films. Domain structure appear, when they are magnetized reversal, in the inner as well as in the outer loops…
A method for estimating the number and position of individual thermoluminescence (TL) peaks within a complex glow-curve is described. The method involves partially heating the sample to a temperature TStop cooling to room temperature and re-heating to record all of the remaining glowcurve. The position of the first ma…
Measurements of the electron spin–lattice relaxation rate are reported for Er3+, Dy3+, and Yb3+ in the cubic host Cs2NaYCl6. Expressions for the anisotropic direct relaxation rates of the respective Γ8 and Γ6 ground states are given in terms of the eleven coupling parameters of the dynamic orbit–lattice interaction fo…
Using a simple Ginzburg-Landau theory which incorporates the crystal symmetry of Nb${\mathrm{Se}}_{3}$, we show that the approximate relation, $2({\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}}_{1}+{\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}}_{2})\ensuremath{\simeq}(1, 1, 1)$, between the two charge-density-wav…
We have measured the temperature dependence of the hydrogen spin lattice relaxation time in the hydride (β, β′, γ, δ) and solid solution phases of the Mg2NiHx system. These gave the temperature ranges of the various phases. The hydrogen diffusion activation energy for the β, β′, γ and δ hydride phases were found to be…
It has been shown that the $D$ band in alkali halides containing ${s}^{2}$ ion (${\mathrm{Tl}}^{+}$, ${\mathrm{In}}^{+}$, ${\mathrm{Ga}}^{+}$, ${\mathrm{Sn}}^{2+}$) is composed of three bands (named ${D}_{1}$, ${D}_{2}$, ${D}_{3}$ in the order of increasing energy). Of the three bands, the ${D}_{1}$ band is the weakes…
The correct normalization of the asymptotic theory for core-level x-ray photoemission spectra of metals has been found. A method for fast convergence of spectra for finite systems as the size becomes large is described. Comparison of asymptotic theory to exact numerical results is made.
The polarized fluorescence band at 3.0 eV which can be produced by photoexcitation of the 6.1-eV $F$ band in high-purity $\ensuremath{\alpha}$-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ has been studied over the temperature range 4.4-300 K. The centroid and zeroth moment of the band remain relatively constant with increasi…
A theory for inelastic Mie scattering from rough metal surfaces or metal sols is proposed. A resonant excitation of a localized dipolar plasmon can enhance the cross section, and experimental data relating to the phenomenon in silver and copper are presented. Two distinct effects are noted. One is inelastic light scat…
We have measured the temperature dependence of the velocity of 10-MHz ultrasonic pulses which were propagated along the layers of the dichalcogenides $2H$-Ta${\mathrm{S}}_{2}$, $1T$-Ta${\mathrm{S}}_{2}$, and $2H$-Nb${\mathrm{Se}}_{2}$. In $2H$-Ta${\mathrm{S}}_{2}$ the plate mode velocity shows little temperature depen…
The organic donor hexamethylenetetrathiafulvalene (HMTTF) forms charge-transfer salts with both tetracyano-$p$-quinodimethane (TCNQ) and its tetrafluoro derivative (TCNQ${\mathrm{F}}_{4}$). We report here the preparation, structure, and conductivity of HMTTF-TCNQ${\mathrm{F}}_{4}$. This salt is found to be isostructur…
We have studied the localized vibrational modes of boron in heavily doped Si using Raman scattering for carrier concentrations of 5\ifmmode\times\else\texttimes\fi{}${10}^{18}$ to 1.5\ifmmode\times\else\texttimes\fi{}${10}^{20}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. The line shapes and positions of the local mode and opt…
The phonon dispersion curves of the fast ionic conductor ${\mathrm{Li}}_{3}$N have been determined in the high-symmetry directions $\ensuremath{\Sigma}$, $\ensuremath{\Delta}$, and $T$ by coherent inelastic neutron scattering at room temperature. The elastic constants ${c}_{11}$, ${c}_{33}$, ${c}_{44}$, and ${c}_{66}$…
We have investigated the single-crystal ionic conductivity of Na5YSi4O12. The conductivity is found to exhibit a thermally activated temperature dependence between 200 and 500 K with activation energies of 0.221 and 0.203 eV parallel and perpendicular to the hexagonal c axis. Room-temperature conductivities were deter…
Single crystals of N${\mathrm{H}}_{4}$${\mathrm{N}\mathrm{i}[{\mathrm{S}}_{2}{\mathrm{C}}_{2}{(\mathrm{CN})}_{2}]}_{2}$. ${\mathrm{H}}_{2}$O have been grown. The single-crystal resistivity in the high-conductivity direction ($\ensuremath{\rho}\ensuremath{\simeq}20$ \ensuremath{\Omega} cm) is the lowest observed for sa…
Valence-band spectra from single crystals of Ir${\mathrm{O}}_{2}$ reproduce the general features of a recent band-structure calculation. Good agreement with the unusual asymmetric core-electron line shapes is obtained by a perturbation-theory treatment of the $d$-electron many-body screening response.
The various effects that can occur when the primary electron energy, ${E}_{p}$, is varied in a reflection-energy-loss experiment are considered. For ${E}_{p}\ensuremath{\ge}100$ eV, the dominant effect is an increase of the electron mean free path with increasing ${E}_{p}$. By performing energy-loss measurements with…