Materials Literature
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The purpose of the paper is to clarify the mechanism of excitation energy transfer between unlike trivalent rare-earth ions in inorganic solids. We have measured the manner in which the intensities of the luminescences of Tb3+ (5D4→7F5) and Eu3+ (5D0→7F2) are quenched and the decay rates are made faster by the coexist…
Abstract The hydration of different forms of magnesium oxide by water vapour was studied at room temperature using gravimetric, X‐ray and electron microscopic methods. It takes place in four steps; formation of a layer of chemi‐ and physisorbed water, transition of magnesium and hydroxide ions in the layer of physisor…
Abstract The crystal structures of Mn 5 O 8 and Cd 2 Mn 3 O 8 are determined from single crystal and high resolution X ‐ray powder data. Both structures have very similar monoclinic unit cells, space group C – C 2/m, and are isotypic: equation image Hence, the true formula of Mn 5 O 8 is Mn Mn O 8 . The crystal struct…
The enthalpy of transformation of a high-pressure form of titanium dioxide, which has the alpha lead dioxide structure, to the rutile modification was measured by the method of "transposed temperature-drop calorimetry." For the reaction, titanium dioxide (alpha lead dioxide form) transforming to rutile, the change in…
A non-linear analysis of cellular convection driven by surface tension in a semi-infinite liquid layer heated from below has been made. The purpose is to determine whether or not one can predict the emergence of the hexagonal flow pattern from the interaction of a certain large class of important disturbances. The pri…
The recovery of the residual electrical resistivities of pure Al and the Al (nominally 0.1 at.%) alloys Al-Mg, Al-Ga, and Al-Ag has been investigated following 1-MeV electron irradiation near 4\ifmmode^\circ\else\textdegree\fi{}K. The addition of solute atoms caused a suppression of recovery normally observed in stage…
The specific heat of 1,3,5-tri-α-naphthylbenzene (TαNB) was measured from 200° to 560°K with a differential scanning calorimeter. The glassy, liquid, and crystalline phases of this material were studied. The latent heat of fusion was found to be 10.14±0.14 kcal mole−1 and the entropy of fusion, 21.5±0.3 cal mole−1·deg…
The effect of x irradiation on silver-activated metaphosphate glass was investigated. The optical and ESR absorptions were measured and assigned to Ag2+, Ag2+ and Ag0. Their optical bands have maxima at 275, 315, and 365 mμ, respectively. The silver atoms, stable at 77°K, show little chemical interaction with the matr…
Cadmium pyrovanadate crystallizes in the C2/m space group with lattice parameters a = 7.088(5) Å, b = 9.091(5) Å, c = 4.963(5) Å, β = 103°21(5)′, and z = 2. This crystal is an isostructure of the mineral thortveitite and thus the anion consists of a pair of centrosymmetrically related corner-sharing VO 4 tetrahedra wh…
β-Zn 3 (PO 4 ) 2 crystallizes in the monoclinic space group P 2 1 /c with lattice parameters, a = 9.393(3) Å, b = 9.170(6) Å, c = 8.686(3) Å, β = 125.73(10)°, and Z = 4. The three independent cations are strongly ligated to 4, 5, and 5 oxygen atoms, with average Zn—O bond distances of 1.98 ± 0.09 Å, 2.10 ± 0.10 Å, and…
The paramagnetic resonance spectra of Mn2+ ions in glasses and compounds of the lithium borate system have been investigated at 9.1 and 35 GHz. The spectrum for the Li2O·4B2O3 compound is found to exhibit six very sharp hyperfine lines centered on g=3.3 when observation is made at X band, while at 35 GHz the center of…
Dynamic polarization of fluorine nuclei has been examined with 14 free radicals dissolved in hexafluorobenzene (C6F6) and 1,1,1-trifluoro-2,2,2-trichloroethane (CF3CCl3). The radicals may be broadly grouped by their tendency to produce either positive or negative fluorine NMR enhancement. A large positive enhancement…
Near-normal incidence-reflectance data on vacuum-evaporated white tin films, produced in situ, are presented for incident photon energies from 2.1 to 14.5 eV. In addition, the real part of the refractive index has been measured from 14.5 to 20.5 eV by the critical-angle method. These results are combined with previous…
The enthalpy of formation and absolute entropy of AlH3 at 298.15°K have been measured as −2.73±0.20 kcal/mole and 7.18±0.10 cal/(mole·°K), respectively. The derived Gibbs energy of formation at 298.15°K of 11.11±0.23 kcal/mole indicates AlH3 is unstable with respect to decomposition to the elements.
With a free-electron model for the conduction band, the isotropic and first-order nonisotropic terms of the indirect exchange interaction in the rare-earth metals have been calculated exactly (in second-order perturbation). The results are compared with previous treatments of the problem, all of which utilize some typ…
Measurements were made of the free-induction-decay (FID) and spin-echo amplitudes of ${\mathrm{Fe}}^{57}$ in pure Fe and some of its alloys. Complex spectra are observed consisting of many oscillations often covering a range of many Mc/sec. The amplitudes are very dependent on the pulse length $\ensuremath{\tau}$, the…
Abstract Das Verdampfungs‐Gleichgewicht des Zweistoffgemisches Ameisensäure/Essigsäure wurde bei 760 Torr sowie bei vermindertem Druck (100 und 30 Torr) gemessen. Da die relative Flüchtigkeit beim Übergang von 760 auf 100 Torr beträchtlich, beim Übergang auf 30 Torr nur noch mäßig ansteigt, erscheint eine Trennung bei…
Monoenergetic electrons of energies from 3.2 to 14 MeV provided by a linear accelerator have impinged normally on thick solid targets. Backscattered electrons have been detected by an ionization chamber, the multiplication factor of which was calibrated with a Faraday chamber as a function of average energy per backsc…
The observation of internal field emission (Fowler-Nordheim tunneling) in magnetically ordered insulators is reported. A large magnetic field effect was observed and interpreted as a decrease in the barrier height due to spin ordering.
Abstract A range of dense well oriented graphites of high chemical purity has been prepared by stress recrystallization of pyrolytic material. Systematic trends in the galvanomagnetic and thermoelectric properties have been investigated in relation to c-axis distribution function, crystallite size, and basal plane dis…