Table of contents

The rate of relaxation of zigzag single-walled carbon nanotubes is calculated by consideration of three-phonon Umklapp process. The results show that the relaxation rate increases exponentially with phonon frequency at low frequency. The linear dependence of the relaxation rate on temperature is obtained. It is shown that the value of the phonon mean free path reaches a few micrometres, which is consistent with the estimated experimental result.

We report the observation of strong second-harmonic radiation from a thin silver film containing randomly distributed small holes. A pulsed laser beam of wavelength 1064 nm impinges at an angle of incidence 45° on the film, and the reflection is collected by a CCD detector and analysed by a high-resolution spectrometer. Strong second-harmonic radiation was observed at the wavelength of 532 nm with a halfwidth of 40 nm.

The microscopic dynamics of glass-forming materials, especially polymers, is a topic of strong current interest and often heated debate. In this review an overview of the most common dynamical phenomena in glass-forming polymers will be presented: α relaxation, β relaxation, 'boson peak', and 'fast process' (β_fast relaxation). The experimental results presented will be mainly from inelastic and quasielastic neutron scattering. Several mostly unanswered questions arise from the experimental findings, e.g.: Is the α relaxation of heterogeneous or homogeneous origin? Is there any relation between the ubiquitous low-temperature vibrational properties of glasses and the α relaxation? Different theoretical and model approaches will be mentioned, e.g. mode-coupling theory, the coupling model, the vibration–relaxation model. The limitations of these attempts will be demonstrated leading to the conclusion that currently there is no theory describing the microscopic dynamics of polymers completely over the whole temperature range from the glassy to the liquid (rubbery) state. Nevertheless, for certain temperature ranges or individual phenomena, especially the β relaxation, successful concepts could be developed.

Hydrogen makes the simplest molecular liquid. Nonetheless, due to several different reasons, measuring its microscopic structure has been one of the most challenging tasks in neutron diffraction experiments. The recent development of modern pulsed neutron sources triggered a renewed experimental interest which, in turn, led to new knowledge and also to a more effective use of the classic reactor-based experimental data. The contemporary development of quantum mechanical computer simulation techniques, and a critical comparison among the results of different experiments using steady and pulsed neutron sources, resulted in a quantitatively reliable solution of the problem.

We investigate theoretically how the confining walls of a nematic cell affect the interaction of particles mediated by the elastic deformation of a nematic liquid crystal. We consider the case where strong homeotropic or planar anchoring is imposed on the flat parallel walls so that the director on the wall surfaces is fixed and uniform alignment is achieved in the bulk. This set-up is more realistic experimentally than any other previous theoretical studies concerning the elastic-deformation-mediated interactions that assume an infinite medium. When the anchoring on the particle surfaces is weak, an exact expression of the interaction between two particles can be obtained. The two-body interaction can be regarded as the interaction between one particle and an infinite array of 'mirror images' of the other particle. We also obtain the 'self-energy' of one particle, the interaction of a particle with confining walls, which is interpreted along the same way as the interaction of one particle with its mirror images. We show that the walls play a different role in homeotropic and planar cells, which is attributed to the difference in the symmetry of the cells. We also present the landscapes of the interaction energy when one particle is fixed and demonstrate that the interaction is sensitively dependent on the fixed particle as well as the interparticle distance.

A model is developed to explore some important issues, such as the effects of the rate of shear on the mixing of the liquid charges, the actual solute distribution at the start of the diffusion anneal period and the effect of a local reduction in liquid charge diameter on the measurement of a liquid diffusion coefficient. A numerical simulation with a grid sliding technique was used to simulate the movable computational domain. The computed results show that the shearing rate has only a small effect on the initial distribution of the solute at the moment when the two liquid columns become aligned, and that the region over which the solute concentration changes from that of the solvent charge to that of the solute-rich charge of the diffusion couple will be very narrow. However, the simulated results reveal that strong convection is produced due to shearing and that the disturbed region is much bigger than the zone over which the solute distribution is disrupted. The convection induced by shearing dissipates within 8 s after the termination of the shearing action for a shear cell with liquid column of 1.5 mm diameter and shear at rates of 4–40 mm s⁻¹. The simulated results also indicate that a small void (approximately one-sixth of the diameter cross-section) in the liquid solvent near the sheared interface does not affect development of the initial solute concentration profile and its subsequent change with diffusion through the interface.

AgI-based fast-ion conducting glasses with very high AgI compositions from the (AgI)_x(AgPO₃)_1−x, (AgI)_x(Ag₂PO_3.5)_1−x, and (AgI)_x(Ag₃PO₄)_1−x systems were prepared successfully by using a rapid-press quenching and a twin-roller quenching method. The ac dielectric measurements showed common relaxation properties of Ag⁺-ion conduction in the glasses independently of the species of the glass network formers of AgPO₃, Ag₂PO_3.5, and Ag₃PO₄, and the activation energies, Δε_a, for Ag⁺-ion conduction were observed to converge upon the same magnitude of ∼26 kJ mol⁻¹ at the AgI composition limit of x = 1. This indicates the formation of amorphous AgI regions in the glasses, and the value of Δε_a = 26 ± 1 kJ mol⁻¹ estimated at x = 1 was concluded to correspond to that for bulk amorphous AgI which has never been obtained experimentally.

The focus of this work is the bonded contribution to the intrinsic Helmholtz free energy of molecules. A weighted density approximation (WDA) for this contribution is presented within the interaction site model (ISM) for ring and cage polymers. The resulting density functional theory (ISM/WDA) for these systems is no more complex than theories for a pure simple fluid, and much less complex than density functional approaches that treat the bonding functional exactly. The ISM/WDA bonding functional is much more accurate than either the ISM/HNC or ISM/PY bonding functionals, which are related to the reference interaction-site model (RISM)/HNC and RISM/PY integral equations respectively, for ideal ring polymers. This means that the ISM/WDA functional should generally be more accurate for most 'real' ring or cage polymer systems when any reasonable approximation for the 'excess' contribution to the intrinsic Helmholtz free energy is employed.

We investigate the tangent-plane n-atic bond-orientational order on a deformable spherical vesicle to explore continuous shape changes accompanied by the development of quasi-long-range order below the critical temperature. The n-atic order parameter ψ = ψ₀e^inΘ, in which Θ denotes a local bond orientation, describes vector, nematic and hexatic orders for n = 1, 2 and 6 respectively. Since the total vorticity of the local order parameter on a surface of genus zero is constrained to 2 by the Gauss–Bonnet theorem, the ordered phase on a spherical surface should have 2n topological vortices of minimum strength 1/n. Using the phenomenological model including a gauge coupling between the n-atic order and the curvature, we find that vortices tend to be separated as far as possible at the cost of local bending, resulting in a non-spherical equilibrium shape, although the tangent-plane n-atic order expels the local curvature deviation from the spherical surface in the ordered phase. Thus the spherical surface above the transition temperature transforms into ellipsoidal, tetrahedral, octahedral, icosahedral and dodecahedral surfaces along with the development of the n-atic order below the transition temperature for n = 1, 2, 3, 6 and 10 respectively.

Strange generation and subsequent extinction of crystal nuclei were observed in the glassy state of salol (phenyl salicylate) during the course of ageing at very low constant-temperatures. The presence/absence of crystal nuclei within the glass were judged, by using a differential scanning calorimeter (DSC), from whether the crystal growth and fusion phenomena were observed in the following heating process or not. The liquid sample was cooled rapidly at 200 K min⁻¹ from 333 K above the fusion temperature down to a desired ageing temperature (T_a) below the glass transition temperature (T_g = 220 K), aged there for different periods (t_a), and then heated up to 213 K at 200 K min⁻¹. The DSC measurement was carried out at 10 K min⁻¹ from 213 to 333 K. The ageing periods were taken in a range between 30 s and 316 min. At T_a = 213 K, crystal nucleation was found to proceed for ageing longer than 100 min. No crystal nucleation was found at T_a in between 123 and 193 K. At T_a below 113 K, crystal nuclei were found immediately after the rapid cooling, then extinguished, and again generated; some nuclei formed initially, survived for longer ageing at 103 K. The generation and extinction phenomena of crystal nuclei are discussed as a general event occurring in glasses located in an extremely non-equilibrium state.

The optical absorption and luminescence properties of indium-doped sodium borate glass irradiated by γ-rays and by powerful UV lasers within the impurity-related absorption band are investigated experimentally. It is demonstrated that both the laser- and γ-irradiation cause similar transformations of optical spectra in the UV and visible regions. The changes of the spectra observed are described with the use of a model which includes three types of impurity centres formed by differently charged indium ions.

We use the classical version of the density-functional theory in the weighted-density approximation to build up the entire phase diagram and the interface structure of a two-dimensional lattice-gas model which is known, from previous studies, to possess three stable phases—solid, liquid, and vapour. Following the common practice, the attractive part of the potential is treated in a mean-field-like fashion, although with different prescriptions for the solid and the fluid phases. It turns out that the present theory, compared to similar theories in the continuum, is of worse quality. Nevertheless, at least a number of qualitative facts are reproduced correctly: (i) the existence of three phases; (ii) the disappearance of the liquid phase when the range of the attraction is progressively reduced; and (iii) the intrusion, just below the triple-point temperature, of a liquid-like layer at the interface between the coexisting solid and vapour phases.

A comparative study of the effects of partial substitution of Co for Fe on thermal stability, crystallization and magnetic properties of Co-containing FINEMET and HITPERM alloys series is presented. The difference in metalloid and Nb content between the two alloy series and the presence of Si in the nanocrystals in the case of FINEMET alloys appear as key parameters. A recrystallization process involving the α-Fe type phase in nanocrystalline alloys of both series is evident from thermomagnetic results as a significant decrease in magnetization at the second crystallization stage.

Electron paramagnetic resonance and electron–nuclear double resonance have been used to characterize four Ti³⁺ centres in undoped crystals of potassium titanyl phosphate (KTiOPO₄ or KTP). These 3d¹ defects (S = 1/2) are produced by ionizing radiation (either 60 kV x-rays or 355 nm photons from a tripled Nd:YAG laser), and form when the regular Ti⁴⁺ ions in the crystal trap an electron. Two of these trapped-electron centres are only observed in hydrothermally grown KTP and the other two are dominant in flux-grown KTP. Both of the Ti³⁺ centres in hydrothermally grown crystals have a neighbouring proton (i.e. an OH⁻ molecule). In the flux-grown crystals, one of the Ti³⁺ centres is adjacent to an oxygen vacancy and the other centre is tentatively attributed to a self-trapped electron (i.e. a Ti³⁺ centre with no stabilizing entity nearby). The g matrix and phosphorus hyperfine matrices are determined for all four Ti³⁺ centres, and the proton hyperfine matrix is determined for the two centres associated with OH⁻ ions. These Ti³⁺ centres contribute to the formation of the grey tracks often observed in KTP crystals used to generate the second harmonic of high-power, near-infrared lasers.

The effect of lanthanum deficiency on structural, magnetic, transport, and electron magnetic resonance (EMR) properties has been studied in a series of La_1−xMnO₃ (x = 0.01, 0.05, 0.11, 0.13) single crystals. The x-ray diffraction study results for the crystals were found to be compatible with a single phase of orthorhombic symmetry. The magnetization curves exhibit weak ferromagnetism for all samples below 138 K. It was found that both the spontaneous magnetization and the coercive field increase linearly with x. The pressure coefficient dT_N/dP decreases linearly with self-doping, from a value of 0.68 K kbar⁻¹ for La_0.99MnO₃ to 0.33 K kbar⁻¹ for La_0.87MnO₃. The resistivity of low-doped La_0.99MnO₃ crystal is of semiconducting character, while that of La_0.87MnO₃ depends weakly on temperature between 180 and 210 K. It was found that the magnetic and transport properties of the self-doped compounds may be attributed to a phase separation involving an antiferromagnetic matrix and ferromagnetic clusters. The latter phases as well as their paramagnetic precursors have been directly observed by means of EMR.

This paper investigates the relation between the temperature dependence of magnetoresistance (MR) and spin frustration in LaMnO_3+δ when Ni is doped into the Mn site. The specimens experience magnetic frustration introduced by the competition between antiferromagnetic (AFM) and ferromagnetic (FM) interactions. According to the temperature dependence of magnetization after cooling the specimen in zero field and non-zero field, Ni-doped specimens behave like cluster glasses. This magnetic frustration at the low temperature is believed to result from the disordered spin structure between AFM and FM phases in these specimens. When the structural symmetry in the specimen is higher, the FM arrangement increases by double the exchange interaction. However, MR decreases in the same temperature region for the same reason. We suggest that the temperature dependence of MR below the Curie temperature in the Ni-doped specimen is controlled by the change of magnetization that occurs with structural change.

A mean field theory of dipolar relaxation in a system of interacting dipoles is developed on the basis of a local field picture. The distribution of orientations of a selected dipole is assumed to satisfy a rotational diffusion equation of Smoluchowski type with time-dependent potential determined self-consistently from the mean dipole moment. The response to an oscillating Maxwell field acting in a volume element is studied for arbitrary amplitude and frequency of the field. For weak field the theory is similar to that developed by Debye, who used the Lorentz local field factor, and derived an expression for the frequency-dependent susceptibility of Clausius–Mossotti form. In the present theory the local field factor is found from the static linear response in thermal equilibrium. The same local field factor is used for strong field. Then the mean dipole moment oscillates anharmonically, and the maximum absorption shifts to higher frequency.

Long-lived photoinduced absorption and dichroism in the Ca₃Ga_2−xMn_xGe₃O₁₂ garnets with x < 0.06 were examined versus temperature and pumping intensity. Unusual features of the kinetics of photoinduced phenomena are indicative of the underlying electronic processes. The comparison with the case of Ca₃Mn₂Ge₃O₁₂, explored earlier by the authors, permits one to finally establish the main common mechanisms of photoinduced absorption and dichroism caused by random electric fields of photoproduced charges (hole polarons). The rate of their diffusion and relaxation through recombination is strongly influenced by the same fields, whose large statistical straggling is responsible for a broad continuous set of relaxation components (observed in the relaxation time range from 1 to about 1000 min). For Ca₃Ga_2−xMn_xGe₃O₁₂, the time and temperature dependences of photoinduced absorption and dichroism bear a strong imprint of structure imperfection increasing with x.