Table of contents

Experiments to determine the resistivity and charge-carrier mobility in semiconducting carbon nanotubes are reviewed. Electron transport experiments on long chemical-vapour-deposition-grown semiconducting carbon nanotubes are interpreted in terms of diffusive transport in a field-effect transistor. This allows for extraction of the field-effect and saturation mobilities for hole carriers, as well as an estimate of the intrinsic hole mobility of the nanotubes. The intrinsic mobility can exceed 100 000 cm² V⁻¹ s⁻¹ at room temperature, which is greater than any other known semiconductor. Scanned-probe experiments show a low degree of disorder in chemical-vapour-deposition-grown semiconducting carbon nanotubes compared with laser-ablation produced nanotubes, and show conductivity and mean-free-path consistent with the high mobility values seen in transport experiments. The application of high-mobility semiconducting nanotubes to charge detection and memory is also reviewed; it is shown that single electronic charges may be detected with a semiconducting nanotube field-effect transistor at operating temperatures up to 200 K.

Radiation-enhanced diffusion, or RED, has been conventionally studied under the conditions of steady state and homogeneous background of excess defects. Hence MeV ion irradiation and diffusion annealing were conducted simultaneously and the temporal and spatial dependences of the diffusing parameters were ignored. This review covers a new type of RED, i.e. non-steady-state radiation-enhanced diffusion or NSRED. The sequence of steps in NSRED are (i) keV ion irradiation of the substrate to create defects, (ii) evaporation of the diffusing materials onto the surface, followed by (iii) diffusion annealing. Using such a sequence, the diffusion region directly overlaps with the central region of the ion implantation profile. Ti diffusion in ion pre-irradiated MgO(100) was selected as a model diffusion system, ions of Ar⁺, Ne⁺, Kr⁺, Cl⁺ and Cr⁺ were used for irradiation and diffusion was conducted in an inert atmosphere. Secondary ion mass spectroscopy (SIMS) was used to depth-profile the diffusing materials. A phenomenological model based on the concept of depth-dependent diffusion coefficients was developed to quantify the NSRED results. Monte Carlo (TRIM) simulations were used to model the implantation. Compared to conventional RED, vacancy clusters, rather than excess mono-vacancies, are the dominant contributors to NSRED, resulting in two unique observations. The first is a post-irradiation annealing effect, i.e. annealing a pre-irradiated substrate enhances the subsequent diffusion. This is due to the key roles of vacancy clusters in the diffusion enhancement. The second is a chemical effect, i.e. the enhanced diffusion does not only depend on the ballistic behaviours of the irradiating ions, as in conventional RED, but on the chemical properties of the ions as well. This effect is consistent with a modified vacancy-clustering model. The results indicate that NSRED is a promising technique for modification of the optical and mechanical properties of oxides through manipulation of doping ion diffusion behaviours in a well-controlled manner.

The crystal structure of LiSrAlF₆-III (P 2₁/c, Z = 4) occurring above 3.0 GPa at room temperature was studied with synchrotron angle-dispersive x-ray powder diffraction in a diamond anvil cell. It was solved by combining a global optimization and a topological analysis with the Rietveld method using rigid-body AlF₆ geometrical constraints. LiSrAlF₆-III, related to LiBaCrF₆ (P 2₁/c, Z = 4), is built of deformed SrF₁₂ icosahedra within a three-dimensional framework of corner-sharing distorted AlF₆ octahedra and LiF₄ tetrahedra, whereas the low-pressure phases I (, Z = 2) and II (P 2₁/c, Z = 4) have cations exclusively in distorted octahedral coordinations. The pressure-induced changes of the coordination polyhedra in the series LiSrAlF₆-I, LiSrAlF₆-II to LiSrAlF₆-III are similar to the differences in coordination polyhedra due to the increase of the ionic radii of the Sr²⁺ and Ba²⁺ cations in LiSrAlF₆-I and (, Ga, Cr, V, Fe, or Ti) at ambient conditions. These observations are discussed on the basis of the high-pressure high-temperature systematics in AB₂X₆ compounds.

The results of high resolution TDPAC measurements of electric quadrupole interaction (EQI) at the ¹⁸¹Ta probe ion in the polycrystalline intermetallic compound Hf₂Co of the Ti₂Ni structure type, in a temperature range from 77 to 1200 K, are presented. The results show the presence of two independent EQIs. At room temperature their frequencies are ω_Q1 = 36(3) Mrad s⁻¹ at the 16c, and ω_Q2 = 230(3) Mrad s⁻¹ at the 48f position. The low frequency interaction is characterized by an unusual temperature dependence which shows a pronounced maximum. The temperature dependence of all relevant physical parameters (the electric field gradient (EFG) principal component V_ZZ, the EFG distribution parameter δ, the asymmetry parameter η, and the fractions of ions contributing to the specific interaction) are also presented. In addition, the EFG parameters of the same structure are calculated using the full-potential linearized augmented plane-wave (FP-LAPW) method as implemented in the WIEN97 package, and the results are compared with the measured data and some previous calculations obtained using the full-potential linear muffin-tin orbital (FP-LMTO) method in the atomic sphere approximation (ASA).

The phonon spectrum of C₃N₄ with defect zincblende-type structure (δ-C₃N₄) was calculated by density functional theory (DFT) techniques. The results permit an assessment of important mechanical and thermodynamical properties such as the bulk modulus, lattice specific heat, vibration energy, thermal expansion coefficient, and thermal Grüneisen parameter. The thermal Grüneisen parameter of δ-C₃N₄ is calculated to be about 1.19 at 300 K, comparable to that of diamond. The coefficient of linear thermal expansion of this structure is calculated to be about 2.2 × 10⁻⁶ K⁻¹ at room temperature. The thermal conductivity coefficient of δ-C₃N₄ is also estimated using Slack's theory to be as high as about 216 W m⁻¹ K⁻¹.

Low-frequency Raman spectra of normal and pressure-densified silica are investigated. Strong suppression of fast relaxation intensity is found in densified silica in comparison with the normal type, the dependence of the fast relaxation intensity versus the density changing its behaviour near the density of the low-density crystalline SiO₂ polymorphs. The light–vibration coupling coefficients extracted from the comparison of Raman spectra and the vibrational density of states are different for densified and normal silica. In the case of the most densified sample, the position of the boson peak maximum marks the transition from the square frequency behaviour of the coupling coefficient to the linear one.

The fractional-dimensional space approach (FDSA) is used to analyse the temperature dependence of direct interband transitions in Si. The critical point (CP) parameters are obtained. The results obtained by the FDSA show general or even better agreement with the theoretical calculation than the standard treatment. In the temperature range of 20–450 °C, the results obtained by FDSA indicate that the excitonic effects can be ignored, and the CP can be treated as a band character. Our research shows that the FDSA provides a good way to derive basic information on relevant physical quantities from the observed optical spectra, and it has the advantages of directness, flexibility, and sensitivity, which enable us to obtain the CP parameters efficiently without ambiguity. This method is especially useful in the cases where the limitations of the standard treatment are serious.

Low temperature synchrotron x-ray diffraction data confirm that a temperature induced structural transformation accompanies the previously reported first-order magnetic transition in Gd₅Si_xSn_4−x (x = 0 and 0.4). The structural change is from the orthorhombic Pnma Gd₅Ge₄-type (room temperature) to the orthorhombic Pnma Gd₅Si₄-type (low temperature). The transformation in Gd₅Sn₄ is not complete by 20 K, with about 13% of the high temperature Gd₅Ge₄-type structure remaining. These results are in excellent agreement with previous Mössbauer and magnetic measurements.

By measuring the strain across the premartensitic transition without and with external dc magnetic fields applied along the [001] and [010] directions of the parent phase, respectively, the characteristics of the premartensitic transition strain is investigated in detail. It was found that not only does the premartensitic transition temperature pronounce a more rapid decrease, but the premartensitic transition strain also exhibits a larger change for a field applied along the [010] direction than does a field along the [001] direction. In accord with a previous model, the present results confirm that the magnetoelastic interaction is responsible for the premartensitic transition, and the magnitude of the magnetoelastic interaction in the [010] direction is stronger than that in the [001] direction.

We have studied the electronic structure of the layered semiconductor TlS by means of ²⁰³Tl and ²⁰⁵Tl NMR and band structure calculation. The crystal structure of this compound is built from the metal–chalcogen layers formed of linked Tl³⁺S₄²⁻ tetrahedra and Tl⁺ ions located between the layers. Our experiments show significant interlayer indirect exchange coupling of thallium nuclei. Since the distances between thallium ions essentially exceed the sum of their ionic radii, it is concluded that such coupling is realized due to the overlap of the Tl electron wavefunctions across the intervening S atom. The exchange interaction has been evaluated by means of the quantitative spectral analysis. The band structure calculation shows that the top of the valence band is composed of mixed Tl⁺ 6s6p_z–S 3s3p_z–Tl³⁺ 6s6p_z states, yielding overlap of the Tl⁺–S–Tl³⁺ type. Such electronic structure gives rise to the effective interlayer coupling of Tl nuclear spins observed in the experiment. This effect is discussed along with the recently obtained NMR results in the chain thallium sulfide and selenide.

The results of electronic structure calculations for PbF₂ in ambient and high-pressure phases are reported here. We employ the linear combination of atomic orbital-density functional theory approximation using the CRYSTAL program package whose capabilities were expanded to include the so-called soft-core pseudopotentials with higher-order components (e.g. d, f, and g) of the angular momentum terms for heavier atoms in the periodic table. The band structure and density of states of the cubic, orthorhombic, and hexagonal phases were calculated. A direct band gap at X is predicted for the cubic phase, whereas an indirect band gap is predicted for the high-pressure phases. The density of states reveals hybridization features involving Pb s and F p orbitals in the upper valence band of PbF₂.

I report systematic first-principles calculations of the quaternary Heusler alloys, e.g. Co₂[Cr_1−xMn_x]Al, Co₂Mn[Al_1−xSn_x] and [Fe_1−xCo_x]₂MnAl. I show that these alloys are also half-ferromagnets when the normal Heusler compounds corresponding to concentration values of zero and unity are half-metals. Moreover, the total spin moment M_t in μ_B scales linearly with the total number of valence electrons Z_t (and thus with the concentration x) following the relation M_t = Z_t−24, independently of the origin of the extra valence electrons, confirming the Slater–Pauling behaviour of the normal Heusler alloys. These results pave the way for experimentalists searching for new half-metallic alloys.

Experimental results on AC susceptibility, DC magnetization, electrical resistivity and magnetoresistivity up to 8 T have been obtained for a well annealed polycrystalline sample of the novel ternary aluminide U₂Co₆Al₁₉. As a reference, similar experiments on the Th counterpart were also done. The U-containing aluminide exhibits two phase transitions at 8 and 12.5 K, probably of ferromagnetic and antiferromagnetic type, respectively. Moreover, U₂Co₆Al₁₉ is a Kondo system showing the coherence effect below about 40 K. On the other hand, the Th counterpart showed unexpectedly a spin fluctuation behaviour, which was inferred from the broad maximum seen in its χ(T) dependence near 600 K. However, the low temperature variation of ρ(T) leads rather to an AT^5/2 power dependence instead of to the AT² one characteristic for a spin fluctuation behaviour.

This work is a theoretical study of the defect creation and annealing, and of the photoconductivity degradation of an intrinsic a-Si:H film under continuous illumination. A new model is developed for the Staebler–Wronski effect (SWE). In this model, we consider that a defect of the SiHD type is locally created by a non-radiative recombination at a weak bond close to a SiHHSi configuration. Also, it is considered that the light induced defect (LID) annealing requires a hydrogen diffusion motion. Using the fact that the areas of defect Gaussians increase with illumination time while their positions and widths remain unchanged, we present the evolution of the gap state defect density, calculated by the defect pool model, with illumination time. This density of states, which varies during illumination, is introduced in the simulation of the photoconductivity to obtain its degradation. In addition, the validity of the proportionality of the photoconductivity to the illumination intensity G and to the inverse dangling bond density is assessed. Our investigations show a monomolecular behaviour of the photoconductivity for moderate intensity. They also show an illumination intensity dependency on G^α, with α varying between 0.5 and 1, in agreement with a large number of similar investigations.

The electron–electron scattering rate (1/τ_ee) in the presence of a random disorder potential has been computed, within the random phase approximation, as a function of excitation energy (ε) for a quantum well (QWL), a quantum wire (QWR) and a periodic quantum wire structure (QWS). It is found that: (i) 1/τ_ee goes to zero when and (ii) the ε dependence as well as the magnitude of 1/τ_ee are determined by the value of the inverse electron–impurity collision time (1/τ), the carrier density and the width of a QWR. The computed 1/τ_ee exhibits its maximum value for and it decreases thereafter on increasing 1/τ, for all values of ε and other parameters. The computed 1/τ_ee of a QWR declines monotonically with the width of the QWR and it reduces to 1/τ_ee of a QWL at larger wire widths, for a given value of ε and the other intrinsic parameters. The 1/τ_ee of a QWS differs from that of a QWR because of the added contribution from inter-wire electron–electron interactions in a QWS. For the given values of ε, 1/τ, carrier density and the width of a QWR, the 1/τ_ee of a QWS is found to be smaller than that of a QWR and larger than that of a QWL. This suggests that the electron–electron scattering rate is enhanced on the reduction in the effective dimensionality of a system. Our theoretical study of 1/τ_ee and its dependence on various intrinsic parameters of QWL, QWR and QWS suggests, in conclusion, that a quasi-particle Fermi liquid description can be applied to electron–electron scattering in the presence of an electron-disorder potential scattering, at zero temperature, in low-dimensional systems.

Ramp-type junctions of p-type La_2/3Ca_1/3MnO₃ (LCMO) electrodes with n-type Eu₂CuO₄ (ECO) barriers have been fabricated by rf magnetron sputtering, photolithography and ion beam etching. A tunnelling effect was observed in junctions with colossal magnetoresistive materials. Interestingly, a discontinuity was observed in the I–V curves below the metal–insulator transition temperature (T_p) of LCMO electrodes. With increasing current, the voltage across the junction increases linearly at first, then deviates from linearity, then a discontinuity occurs and finally the voltage recovers its linearity. With changing temperature, the discontinuity in the I–V curves happens at the same voltage of 209 mV, but starts at different currents. The discontinuity starting current (I_c) decreases with increase of the temperature. The discontinuity disappears above T_p. There is a hysteresis near the discontinuity when the current increases and decreases. The discontinuity in the I–V curves could indicate a novel switching process. This switching phenomenon occurs only in the ferromagnetic metal state and strongly suggests a magnetism related effect. The physics of the switching process has not been understood yet, but it could be of interest for potential applications in spintronics devices.

Strong interaction between fermions may lead to a novel quantum ground state where the rotational symmetry is spontaneously broken while the translational symmetry is still preserved. Such a 'nematic' Fermi liquid has a spontaneously deformed Fermi surface and supports a gapless Goldstone mode associated with the broken rotational symmetry. We consider a nematic Fermi liquid of fermions carrying two internal quantum numbers that, for example, may represent the layer degree of freedom of a bilayer system. It is found that the effective interaction mediated by a collective mode gives rise to a pairing instability of the underlying fermions under certain conditions, leading to the conclusion that the nematic order could be useful for superconductivity.

We present new expressions for the formfactors of local operators for the XX-quantum spin chain as Cauchy determinants. Using the known functional form of the correlator at large distances we propose a new expression for the constant for the asymptotics of the correlator as a Cauchy determinant. We calculate the momentum distribution for the general case of the XXZ-spin chain and point out that it is completely different from that for the Luttinger model (the system of fermions). For the XX chain we compare numerically the value of the lowest formfactor and the expectation value of momentum-zero operators which is determined by the functional form of the correlator.

We report calculations of the magnetic anisotropy energy (MAE) of cobalt nanoparticles in the size range 300–1000 atoms. The MAE is expressed in terms of shell-resolved contributions from different parts of the cluster. The net anisotropy is a delicate balance between contributions from the interior and the surface of the cluster that generally have opposite signs. We study closed shell structures for which the MAE is fourth order in the spin–orbit coupling, and clusters for which additional layers have been added to the facets, inducing uniaxial anisotropy. Both Co and Cu facet additions are considered. The relation of the results to experimental work is discussed.

We report on the structural, magnetic and magnetotransport effects promoted by Nd³⁺ substitution in Nd_xSr_2−xFeMoO₆. In spite of the fact that the ionic radius of Nd³⁺ is smaller than that of Sr²⁺, the unit cell volume remains constant across the series. We also show that the incorporation of Nd³⁺ induces a substantial rising of the Curie temperature from T_C = 400 K for x = 0 to T_C = 440 K for x = 0.6. On the basis of the structural data we argue that this enhancement is due to the injection of itinerant carriers into the conduction band. Nd doping promotes the appearance of antisite (AS) defects in the Fe–Mo sublattice. It turns out that the concentration of AS is mainly controlled by the donor character of the substituting ions rather than by their ionic radii. Antisites are found to reduce the saturation magnetization and the magnetoresistance. This observation, which sharply contrasts with expectations based on electronic rigid band models, indicates that the half-metallic character of double perovskites may be unstable in the presence of antisites. This is in agreement with some recent proposals and the implications of these findings are discussed.

Magnetic ordering of the orthorhombic Er₃Cu₄X₄ (X =  Si, Ge, Sn) system has been studied using both ¹¹⁹Sn and ¹⁶⁶Er Mössbauer spectroscopy, combined with neutron diffraction. We observe two distinct ordering events for the erbium moments on the 2d and 4e sites (T_N (Er 2d)>T_N (Er 4e)) and confirm that the Er 2d moments are larger than those on the Er 4e site. Comparison of neutron diffraction with ¹⁶⁶Er Mössbauer spectroscopy shows that the ordering of the Er 4e moments is far from complete, even at 0.7 T_N, causing neutron diffraction analysis to severely underestimate the Er 4e moments in the Er₃Cu₄X₄ system.

Platinum core–silica shell nanoparticles (Pt@SiO₂) have been applied to the outermost layer of a three-layer film structure to yield a Pt@SiO₂/SiO₂/ITO (indium tin oxide) coating on a glass substrate. Optical properties of the three-layer film have been investigated in the visible spectrum regime. The absorption of visible light by the Pt core–SiO₂ shell layer was higher in low- and high-wavelength regimes while it was minimal at a mid-visible light range, about 550 nm. This characteristic absorption of the core–shell layer resulted in a broad-band anti-reflectance behaviour of the multi-layer coating system in the entire visible light regime. Transmittance of the three-layer coating–glass system was in the range between 80% and 85% and thus the application of the platinum core–silica shell nanoparticle layer with such absorption characteristics is shown to provide flexibility of ways to achieve a broad-band anti-reflectance and transmittance of a multi-layer coating system.

We have performed polarized Raman scattering measurements on several Czochralski-grown lanthanide trifluoride (LnF₃) crystals presenting the β-YF₃ structure (space group: Pnma). The phonon mode assignments for the DyF₃ and LuF₃ spectra are given for the first time. Besides this, the Raman spectra of TbF₃, ErF₃ and YbF₃ complete and extend previous studies on these materials. The vibrational modes of LnF₃ compounds are then correlated with those of the archetype β-YF₃ crystal. The totally symmetrical fundamentals present a strong dependence on the scattering geometry, similar to what is shown by molecular crystals with weakly interacting molecules. Most of the Raman features are well behaved with the lanthanide ion substitution. Although the observed modes always involve all ions, it was possible to discern modes that are dominated by the motion of either the lanthanide or the fluorine ions. The intensity of some low frequency modes has proved to be quite dependent on the orthorhombic distortion of the quasi-hexagonal structure.

We investigate the long-distance propagation of broadband photoluminescence (PL) light inside an annealed Si/SiO₂ superlattice (SL) with repeats of 1.5 nm Si and 2 nm SiO₂ layers deposited on a silica substrate. The SL material annealed at 1150 °C contains Si nanocrystals with diameters of 3–4 nm as estimated by Raman spectroscopy, and the SL layer was estimated to be overall 1.75 µm thick with an effective refractive index of 1.65. As measured in the conventional transverse detection geometry, the SL material exhibits a broad PL band with a maximum at  nm (1.6 eV). Our measurements in the waveguiding detection geometry show wavelength selectivity of optical waveguiding by the SL layer. In fact, efficient narrowing of the PL spectrum (down to 16 meV) takes place upon the propagation of the PL light inside the SL layer for wavelengths of 710 and 960 nm. We observed the guiding of PL light by the SL layer to distances above 5 mm, and the propagation losses for the guided light at 710 and 960 nm were estimated to be 6.2 and 4.7 cm⁻¹, respectively. The attenuation of PL light outside the guided wavelengths is much larger (e.g., at 780 nm) demonstrating that Si/SiO₂ SL-based waveguides can be used as optical filters. The transmittance peaks can be tuned by changing the SL layer optical thickness.

Silica gels dispersed with nanoscale CdS particles were prepared by the sol–gel process combined with γ-irradiation at room temperature and in ambient pressure. X-ray diffraction (XRD) and transmission electron microscopy have revealed the existence of CdS nanocrystals, as well as their structures and size distributions. The silica matrix affects the crystal structure of the CdS particles produced. A prominent quantum size effect was observed through the absorption and luminescence spectra of samples irradiated for different periods of time. The most interesting phenomenon is that on increasing the irradiation time, the surface-state emission disappears, and simultaneously band edge emission appears and becomes even stronger with longer irradiation: this is thought to be due to the passivation effect by the surrounding matrix through the interface electrostatic interactions around the particles.

In order to clarify the growth process and hard to understand reported spectra of iodine film and silver iodide (AgI) film, various spectral transitions have been measured in situ: (a) optical density spectra of films grown on low temperature substrates by vacuum evaporation of an iodine lump, during deposition and annealing; (b) optical extinction spectra of vapour zones produced by gas evaporation of AgI powder, during evaporation; and (c) optical density spectra of films grown on low temperature and room temperature substrates by vacuum evaporation of AgI powder, during deposition and annealing. After these in situ real time measurements, the film specimens were allowed to recover and were examined by means of comparative measurements of the optical density and photoluminescence spectra at about 12 K. The spectra obtained were analysed and compared with those reported previously by other workers, and the following questions have been optically clarified: (1) How does annealing improve the crystal quality of iodine film? (The annealing at about 200 K improves the crystal quality considerably.) (2) What is the film that is quench deposited on low temperature sapphire surfaces by thermal evaporation of AgI powder? (It is Ag_mI_n () dispersed iodine film.) (3) How does AgI film grow in the deposited film? (Above about 220 K, iodine evaporates abruptly to grow uniform AgI film on the substrate.) (4) How does excess iodine affect the optical spectrum of AgI? (The excess iodine creates both several exciton absorptions due to polytype structures at wavelengths between 370 and 410 nm, and a tail at wavelengths longer than 430 nm.) (5) What is the best evaporation condition for the fabrication of AgI and iodine films? (The best quality of iodine and βAgI films can be obtained at a substrate temperature of about 200 K in the quench deposition method.) Besides this, the present optical experiments have answered the following question: is there truly a strongly enhanced optical absorption in quench deposited AgI films, as reported by Kondo et al (1998 Phys. Rev. B 57 13235)? The present studies have elucidated that the enhanced absorption is not due to amorphization of AgI but due merely to intense optical absorption of iodine in the films.

Electronic structures of UTSn (T = Ni, Pd) have been investigated using photoemission spectroscopy (PES). The extracted U 5f PES spectra of UTSn (T = Ni, Pd) exhibit a broad peak centred at  eV below E_F with rather small spectral weight near E_F (N_f(E_F)). The small N_f(E_F) in UTSn is found to be correlated with the T d PES spectra that have a very low density of states (DOS) near E_F. The temperature-dependent high-resolution PES spectra of UTSn provide evidence for the V-shaped reduced metallic DOS near E_F, but they reveal no appreciable changes in their electronic structures across the magnetic phase transition temperatures. Comparison of the measured PES spectra to the LSDA +U band structure calculation shows reasonably good agreement for UPdSn, but not for UNiSn. Therefore, in contrast to the general consensus of the localized U 5f electrons in UTSn (T = Ni, Pd), our finding supports a rather itinerant nature of U 5f electrons for UPdSn, but not for UNiSn.

We perform angle-resolved photoemission spectroscopy on 1T-TaS₂ and 1T-TaSe₂ using synchrotron radiation. We observe a characteristic splitting of the chalcogen p-derived valence bands along high symmetry directions. Density functional theory calculation and group theory strongly suggest that this splitting is due to spin–orbit interaction along one direction, and to symmetry along the other direction. We note that, according to the Kramers degeneracy, the spin–orbit interaction leaves every state doubly degenerate. Furthermore, this study allows us to identify a mixing between bands with Ta 5d and Se 4p character, possibly relevant for the different temperature behaviours of the two compounds.

We present an experimental investigation on the rheological behaviour of model granular media made of nearly elastic spherical particles. The experiments are performed in a cylindrical Couette geometry and the experimental device is placed inside an aeroplane undergoing parabolic flights to cancel the effect of gravity. The corresponding curves, shear stress versus shear rate, are presented, and a comparison with existing theories is proposed. The quadratic dependence on the shear rate is clearly shown, and the behaviour as a function of the solid volume fraction of particles exhibits a power law function. It is shown that theoretical predictions overestimate the experimental results. We observe, at intermediate volume fractions, the formation of rings of particles regularly spaced along the height of the cell. The differences observed between experimental results and theoretical predictions are discussed and related to the structures formed in the granular medium submitted to the external shear.

Simultaneous generation of efficient red, green and blue (RGB) light was achieved by doubling and tripling a diode-pumped, Q-switched 1342 and 1063 nm Nd:GdVO₄ laser using an aperiodically poled LiTaO₃ crystal. Quasi-white colour was obtained by mixing the RGB outputs at 115.8 °C. The average powers of the RGB light were 31.3, 18.4 and 3.7 mW, respectively.

The crystal structure of the ordered double perovskite Ba₂PrRu_0.8Ir_0.2O₆ was investigated as a function of pressure at room temperature. High-resolution synchrotron powder diffraction measurements have revealed the occurrence of a first order phase transition at a critical pressure of about 0.5 GPa. Structural refinements indicate that Ba₂PrRu_0.8Ir_0.2O₆ transforms from an ambient pressure monoclinic (P 2₁/n) to a high-pressure tetragonal (P4/mnc) structure. The transition is consistent with a valence change of the Pr ions.