Many atomically ordered grain boundaries ͑GBs͒ couple to applied mechanical stresses and are moved by them, producing shear deformation of the lattice they traverse. This process does not require atomic diffusion and can be implemented at low temperatures by deformation and rotation of structural units. This so-called coupled GB motion occurs by increments and can exhibit dynamics similar to the stick-slip behavior known in atomic friction. We explore possible dynamic regimes of coupled GB motion by two methods. First, we analyze a simple one-dimensional model in which the GB is mimicked by a particle attached to an elastic rod and dragged through a periodic potential. Second, we apply molecular dynamics ͑MD͒ with an embedded-atom potential for Al to simulate coupled motion of a particular tilt GB at different temperatures and velocities. The stress-velocity-temperature relationships established by both methods are qualitatively similar and indicate highly nonlinear dynamics at low temperatures and/or large velocities. At high temperatures and/or slow velocities, the character of the GB motion changes from stick slip to driven random walk and the stressvelocity relation becomes approximately linear. The MD simulations also reveal multiple GB jumps due to dynamic correlations at high velocities, and a transition from coupling to sliding at high temperatures.

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We report the measurements of the pseudodielectric function, far-infrared reflectivity and Raman scattering spectra in Sr 14 Cu 24 O 41 single crystal. We study the lattice and the spin dynamics of the Cu 2 O 3 spin ladders and CuO 2 chains of this compound. The ellipsometric and the optical reflectivity measurements yield the gap values of 1.4 eV, 1.86 eV, 2.34 eV (2.5 eV) for the ladders (chains) along the c-axis and 2.4 eV along the a-axis. The electronic structure of the Cu 2 O 3 ladders is analyzed using tight-binding approach for the correlated electron systems. The correlation gap value of 1.4 eV is calculated with the transfer energy (hopping) parameters t = t 0 =0.26 eV, along and perpendicular to legs, t xy =0.026 eV (interladder hopping) and U=2.1 eV, as a Coulomb repulsion. The optical parameters of the infrared active phonons and plasmons are obtained by oscillator fitting procedure of the reflectivity spectra. Raman scattering spectra are measured at different temperatures using different laser line energies. The two-magnon peak is observed at about 2880 cm −1 . At temperatures below 150 K the new infrared and Raman modes appear due to the charge ordering.

Thin films of lead tin sulphide PbSnS2 were deposited on glass substrates at 100 °C at vacuum pressure of 3×10–6 mbar using a thermal evaporation method. Scanning electron microscopy (SEM) and X‐ray characterization revealed that thin films were monophase and polycrystalline. The average particle size was approximately 28 nm. Absorption coefficient of PbSnS2 thin films (∼105 cm–1) was found from transmission optical spectroscopy measurements. Its fundamental absorption edge is shown to be 1.65 eV with direct allowed transition recommended for photovoltaic application. Thermoelectric measurements showed the materials to be p‐type in nature. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)