Materials Literature
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The nature and possible origins of the structural distortions in the neighbourhood of the Cr 3+ ion in MgCr 2 O 4 are discussed in the light of experimental evidence from optical, X-ray diffraction, infrared absorption and other investigations. The results of the analysis may have implications for other compounds with…
On the basis of the planar coupling factor it is shown that the maximum in the electromechanical activity at the morphotorpic phase boundary of Pb(ZrxTi1−x)O3 solid solutions is caused by a maximum of the dielectric constant. Starting from an expansion of the free energy similar to that introduced by Devonshire and po…
The ESR spectra of four radicals of the type RĊHCO2−, four of the type RĊ (O−) CO2−, and one each of the types R2ĊCO2− and ROHĊCO2− have been studied and the 13C hyperfine constants determined. The radicals were produced by continuous, in situ radiolysis of basic aqueous solutions of the appropriate acids. In all case…
It is shown that a pure thermal model, in the absence of significant heating of the electrodes, gives no negative differential resistance and no high-current filaments. When some electronic effects, such as space charge, narrow Schottky barriers, or field-enhanced conductivity, are explicitly introduced, negative-resi…
A further study is made of the properties of the simple tight-binding Hamiltonian for which Weaire has recently shown that a band gap exists in a tetrahedrally bonded solid regardless of its structure. An exact transformation of the density of states is found which relates it to that generated by a much simpler Hamilt…
The electronic band structure, charge density, and optical properties of diamond have been calculated using the discrete variational method in an ab initio approach with an LCAO Bloch basis set. This technique avoids most of the difficulties encountered with evaluation of the matrix elements of the Hamiltonian, and al…
The lattice thermal conductivity of germanium has been analyzed on the basis of the Callaway model in the temperature range 2-1100 \ifmmode^\circ\else\textdegree\fi{}K. At high temperatures four-phonon processes are seen to play an important role in the determination of the thermal resistivity of germanium. In order t…
The pyroelectric coefficient (at constant stress) of lithium sulfate monohydrate was measured over the temperature range 4.2-320\ifmmode^\circ\else\textdegree\fi{}K, in order to resolve a discrepancy between the results of Ackermann and those of Gladkii and Zheludev, and to extend the data to below 88\ifmmode^\circ\el…
Nuclear quadrupole resonance of $^{14}\mathrm{N}(I=1)$ has been studied for the two diatomic species $^{14}\mathrm{N}$-$^{14}\mathrm{N}$ and $^{14}\mathrm{N}$-$^{15}\mathrm{N}$ in solid $\ensuremath{\alpha}$-nitrogen. Spectra from carefully prepared and annealed samples display well-resolved intramolecular dipolar spl…
The photochromic properties of transition-metal-doped SrTi${\mathrm{O}}_{3}$ are studied using optical and electron paramagnetic resonance techniques. In addition to the double doped systems containing Fe + Mo, and Ni + Mo, which were treated briefly in earlier publications, the photochromic effect in SrTi${\mathrm{O}…
Crystals of triglycine sulfate (TGS) grown from solutions containing alanine are found to give biased ferroelectric hysteresis loops. The material is therefore always in a fully poled state when below its Curie point in the absence of large external fields. The values of ε′ and ε″ are lower than for pure TGS. Pyroelec…
The three-dimensional analog of Holstein's molecular crystal model is utilized as the basis for a study of the relaxation of the lattice after a small-polaron hop. In particular, it is shown explicitly that the time-dependent activationlike energy arising in the previously developed theory of correlated small-polaron…
Application of dc electric fields, at temperatures of \ensuremath{\sim}100 to \ensuremath{\sim}325\ifmmode^\circ\else\textdegree\fi{}C, to samples of SrTi${\mathrm{O}}_{3}$ doped with transition metals leads to the appearance of colored regions, characteristic of reduced material at the cathode and oxidized material a…
A new electro-optical effect in nematic liquid crystals with negative dielectric anisotropy is described, using sandwich cells with molecular orientation perpendicular to the electrode surface (homeotropic alignment). In an arrangement between crossed polarizers, high-contrast ratios have been achieved with low voltag…
The distribution of magnesium and iron over the M1 and M2 positions in Bamle enstatite shocked at 1 megabar is highly disordered. It corresponds to an equilibrium distribution of at least 1000 degrees C. The distribution in samples shocked at 450 kilobars or less is undisturbed.
The International Association for the Properties of Water and Steam has recently adopted a new formulation for the thermodynamic properties of heavy water. This manuscript describes the development of a new formulation for the viscosity of heavy water that is consistent with the new equation of state and is valid for…
Abstract This paper refers to a method for cal‐culating and determining the distribution along a crevice of given geometrical characteristics of voltage and c. d. ex‐changed between the electrolytic solution and the shielded surface of a metallic material susceptible of active‐passive transition. This method has been…
An explicit classification of lattices and crystallographic groups of 4-dimensional space R4 is given. There are (in R4): 710 arithmetic crystal classes; 227 geometric crystal classes belonging to 118 isomorphism types of groups; 64 Bravais classes corresponding to 64 Bravais types of lattices; 33 crystal systems; 23…
Measurements of orientational and forced magnetoresistances have been done on Gd single crystals in a range from 77 K to 400 K. According to a phenomenological analysis, the four anisotropy constants of the orientational magnetoresistance were determined. The temperature dependence of the orientational magnetoresistan…
An electrolytic sectioning technique has been used to measure self-diffusion coefficients for gold in the temperature range 360 to 740 °C. At 740 °C our value agrees with previous work at this temperature, while the lower temperature values are larger than predicted by extrapolation of the well-established high-temper…