Materials Literature
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We have developed a new technique, based on the standard Monte Carlo simulation method with Markov chain sampling, in which a set of three dimensional particle configurations are generated that are consistent with the experimentally measured structure factor. A(Q), and radial distribution function, g(r), of a liquid o…
The authors investigate the thermodynamics of a lattice gas model for intercalation, employing a nearest-neighbour intra-plane attraction and both attractive and repulsive forces which decrease with increasing distance between the planes. The free energy F is calculated within the mean-field approximation. The phase d…
The magnetic structures of the orthorhombic rear-earth manganates ErMn 2 O 5 and TbMn 2 O 5 have been studied by single-crystal neutron diffraction at temperatures between 1.5 and 25 K. Both materials exhibit amplitude-modulated magnetic structures with propagation vector (0.5, 0, 0.247) (Er) or (0.5, 0, 0.308) (Tb) a…
The current status of the physics of liquid-crystalline polymers is reviewed. Major attention is paid to the theory of the nematic state of solutions and melts of polymers of varying architecture, and also of polyelectrolytes. The conditions for phase equilibrium in solutions and melts and the elastic properties of sy…
Forced Rayleigh scattering is used to measure the self-diffusion of charged polyball suspensions driven far from equilibrium by an oscillating shear flow. Aside from the usual enhancement of the diffusion due to Taylor dispersion, we observe an additional isotropic contribution which increases linearly with the shear…
Studies by small-angle neutron scattering have been conducted on a main-chain thermotropic nematic polymer composed of alternating mesogens and flexible spacers. The anisotropy of chain conformation in the nematic phase was measured in the melt and in a dilute nematic solution. The variation as a function of degree of…
We compare for the first time gas-phase $3s$ and $3p$ spectra from atomic Mn with corresponding spectra from the solid compounds Mn${\mathrm{F}}_{2}$ and MnO. These spectra are found to be strikingly similar, indicating that the solid-state spectra have a dominant origin in unscreened intra-atomic multiplet splittings…
The phase diagram for liquid-crystal models of hard molecules is studied by use of a nonlocal density functional for the free energy. Nematic, smectic-$A$, and smectic-$C$ phases can be obtained from purely packing effects without any attractive interaction. A system of parallel hard spherocylinders shows a continuous…
In a directional solidification experiment on a moving nematic-isotropic interface, we observe solitary modes propagating across the interface. We also observe the Eckhaus instability. In the presence of solitary modes, the pattern-selection mechanism is dynamic.
Optical field induced first-order electric Freedericksz transition and electric bistability in a homogeneously aligned nematic film is first observed. It is experimentally demonstrated that an applied optical field can transform the electric Freedericksz transition from second order to first order. The molecular reori…
Photoemission spectra from potassium adsorbed on an Al{111} surface show a K $4s$-derived state just below the Fermi level, ${E}_{F}$, which is first observed just prior to the onset of ordering in the overlayer. The feature disperses upwards with increasing ${\mathbf{k}}_{\ensuremath{\parallel}}$ and crosses ${E}_{F}…
Loading a cantilevered bar allows studying the effect of a uniform, externally applied, and continuously variable strain field on the properties of surfaces. Straining a nominally flat Si(100) surface produces unequal populations of the 2 \ifmmode\times\else\texttimes\fi{} 1 and 1 \ifmmode\times\else\texttimes\fi{} 2…
A density-functional theory, based on the smoothed density approximation, is presented in order to study phase transitions in systems of hard spherocylinders with full translational and orientational degrees of freedom. We find both the nematic-isotropic and the $\mathrm{n}\mathrm{e}\mathrm{m}\mathrm{a}\mathrm{t}\math…
We present neutron-spin-echo data on the structural relaxation of glass-forming polybutadiene near the glass transition. Microscopic dynamics on the scale of an interchain distance and the monomeric friction coefficient derived from macroscopic viscosity relaxation obey the time-temperature superposition principle fol…
Weak features between 16000 and 19000 cm -1 in the absorption spectra of Cs 2 ReCl 6 and K 2 ReCl 6 are assigned as cooperative absorptions involving coupled excitations of the Gamma 8 ( 4 A 2g ) to Gamma 6 ( 2 T 1g ), Gamma 8 ( 2 T 1g ), Gamma 8 ( 2 E g ) transitions on neighbouring complex ions. The intensity mechan…
Many glasses and liquids exhibit a first sharp diffraction peak that is evidence for intermediate-range order caused by regularities in the packing of structural units. These tend to cluster around particular values of the wavevector when scaled by the nearest-neighbour distance or the mean inter-atomic spacing. The f…
Potassium titanyl orthophosphate KTiOPO 4 has been studied by Raman and infrared reflectivity spectroscopy in the range from a low temperature to room temperature and for various scattering configurations. The absence of a structural phase transition below room temperature is confirmed. The phonon modes are classified…
Magnetic measurement, are performed on R2Fe14–xCrxB compounds (R = Y, Nd, and Gd). These compounds, crystallize in the Nd2Fe14B structure up to x ≦ 3. The Curie temperature and the lattice constants a and c decrease with increasing Cr content. The spin-reorientation temperature in Nd2Fe14B is lowered when Cr replaces…
Samples of composition Nd15(Fe1−xCox)77B8 and La15(Fe1−xCox)77B8 were produced by arc melting and subjected to prolonged heat treatments. Metallographic analysis and x-ray diffraction revealed the presence of the magnetic La2(Fe1−xCox)14B phase in the La-based materials; lattice parameters for x=0–1 were determined. H…
Raman spectra of ZnS heavily doped with Al in the Stokes region of 400 to 500 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ show several distinct lines on the low-energy side of hexagonal-host modes. They are independent of temperature and thus attributed to Al-related local phonons. From vibrational-mode analysis and by…