The slope equations: A universal relationship between local structure and glass transition temperature

In this article, we present a universal relationship between the glass transition temperature and the local glass structure. The derivation of the simplest expression of this relationship and some comparisons with experimental values have already been reported in a recent letter. We give here the analytical expression of the parameter of the Gibbs-Di Marzio equation and also new experimental probes for the validity of the relationship, especially in low modified binary glasses. The influence of medium range order is presented and the unusual behavior of in binary and systems explained by the presence of modifier-rich clusters (denoted by doublets). Received: 3 September 1997 / Received in final form and accepted: 17 November 1997     

Growth and properties of magnetron cosputtering grown MnxGe1−x on Si (001)

We have grown Mn_xGe_1−x films (x=0, 0.06, 0.1) on Si (001) substrates by magnetron cosputtering, and have explored the resulting structural, morphological, electrical and magnetic properties. X-ray diffraction results show there is no secondary phase except Ge in the Mn_0.06Ge_0.94 film while new phase appears in the Mn_0.1Ge_0.9 film. Nanocrystals are formed in the Mn_0.06Ge_0.94 film, determined by field-emission scanning electron microscopy. Hall measurement indicates that the Mn_0.06Ge_0.94 film is p-type semiconductor and hole carrier concentration is 6.07×10¹⁹ cm⁻³ while the Mn_xGe_1−x films with x=0 has n-type carriers. The field dependence of magnetization was measured using alternating gradient magnetometer, and it has been indicated that the Mn_0.06Ge_0.94 film is ferromagnetic at room temperature.     

Optical response of thin plasma-polymer films with non-spherical silver nanoparticles

The size and shape of silver nanoparticles which are embedded in a plasma-polymer matrix were obtained by transmission electron microscopy and analyzed with optical image processing. We used a sample in which silver particles were present before and after reshaping caused by thermal annealing in adjacent regions. As most of the particles appeared as elongated rotational ellipsoids, the major and minor half axis were determined for each particle. We adopted the model of Gans in the Rayleigh approximation to calculate for each investigated particle the extinction spectra from to using the data from the image processing. The various spectra for 368 silver particles were added to get total extinction spectra for the sample as deposited and after reshaping, respectively. We found good agreement with the experimental spectra. The blue shift of the plasma-resonance absorption, which occurs due to the reshaping of the silver particles during thermal annealing, was also confirmed by using only changes in the particle sizes and shapes. Received: 23 July 1997 / Revised: 27 October 1997 / Accepted: 3 December 1997     

Non-linear acoustic measurements to assess crack density in trabecular bone

Three methods to measure qualitative and quantitative aspects of bone non-linearity were investigated in the context of diagnosis of bone “biomechanical health”: i.e. harmonic generation, parametric emission and parametric reception using phase modulation. Trabecular bone exhibited hysteretic non-linear behavior due to microcracks in bone tissue, and parametric reception using phase modulation seemed to be the best configuration for in vivo application. However, the relationship between level of non-linearity and crack density needs to be validated by histological analysis.     

Making amorphous steel in air by rare earth microalloying

Recently great advancement in the fabrication of structural amorphous steels (SASs) with large cross-section sizes has been obtained. One of the remained key problems for the manufacturability and the application of SASs is that their glass-forming ability is very sensitive to the processing environments. Here we present the discovery that the bulk amorphous alloy Fe₄₄Mn₁₁Cr₁₀Mo₁₂C₁₅B₆Ho₂ has high oxygen resistance and can be prepared by conventional copper-mold casting method in air atmosphere. Rod-shaped amorphous samples of diameter up to 6 mm at least have been fabricated successfully. This amorphous steel alloy showed high glass-forming ability and good manufacturability. The beneficial effects of the addition of holmium on the glass-forming ability and oxygen resistance during the SAS formation are explored.     

Supersonic cluster beam deposition of nanostructured titania

Nanostructured titanium dioxide films have been deposited by supersonic cluster beam deposition (CBD). Nanoparticles are produced by a pulsed microplasma cluster source (PMCS) and selected by aerodynamic separation effects. The as-deposited film is a complex mixture where amorphous material coexists, at the nanoscale, with anatase and rutile crystal phases. The nanocrystalline fraction of the film is characterized by crystal size ranging from 100 nm to less than 5 nm. We have characterized the film structure by transmission electron microscopy, Raman spectromicroscopy, X-ray diffraction, and UV-visible spectroscopy showing that correlations exist between cluster size and film properties. In particular if very small clusters are deposited, the film shows a predominant rutile phase whereas larger clusters form films with mainly anatase structure. Our observations suggest that phonon confinement effects are responsible for a significant shift and broadening observed for the Raman peaks. In addition, optical gap tuning is provided by mass selection: large clusters assembling generates a film with 3.22 eV optical gap, while smallest clusters 3.52 eV.     

Copper position in type-I Ba8Cu4Si42 clathrate

Local structure of Cu in a type-I Ba₈Cu₄Si₄₂ clathrate has been investigated by synchrotron X-ray powder diffraction, Cu K-edge extended X-ray absorption fine spectroscopy, X-ray absorption near edge spectroscopy (XANES) and theoretical calculation. It is found that XANES spectra cannot be explained by the substitution of Cu atoms at Si16i, and Si24k positions. Our calculations show that the binding energies of the Si atom in Si16i, Si24k and Si6c positions are 9.000, 9.495 and 8.911 eV, respectively. Both experimental and theoretical results support that Cu atoms in the type-I Ba₈Cu₄Si₄₂ clathrate, as a doped element, prefer to occupy the least-binding Si, i.e., the Si6c sites. No structural change between 112 and 300 K was observed and the (100)-faceted cubic crystal has negligible distortion/ordering according to transmission electron microscopy.     

Synthesis of new La nitrides at high pressure and temperature

We have succeeded in synthesizing two new lanthanum nitrides in a supercritical nitrogen fluid at high pressure (about 30 GPa) and high temperature (about 2000 K), using a diamond anvil cell and a YAG laser heating system. These nitrides were found to be stable down to 5 GPa and ∼300 K in a nitrogen atmosphere. One of the new lanthanum nitrides is a cubic P lattice-type phase, which is a main phase synthesized nitride. The calculated lattice parameter is at 5 GPa, 300 K. The other nitride is of a trigonal P lattice-type. The calculated lattice parameters are and at 5 GPa, 300 K. The most likely phase of the former new La nitride is , the structure of which may be similar to the   Mn₂O₃-type (Ia80). The phase of the latter nitride is , the structure of which is the same as the   La₂O₃-type (hP5).     

Transmission characteristics of wave modes in a rectangular waveguide filled with anisotropic metamaterial

In this paper, transmission characteristics of wave modes in a rectangular waveguide filled with lossless anisotropic metamaterial are theoretically investigated. The wave equation and dispersion relations for TE and TM modes in the waveguide are obtained and analyzed. It is shown that the negative constitutive parameters of the filling anisotropic metamaterial can be used to control the wave magnitude and the phase velocity direction in the waveguide over the entire frequency domain, both below and above the cutoff frequency. Particularly, not only backward waves, but also forward waves can propagate below the cutoff frequency in the waveguide. Furthermore, a typical example is calculated to demonstrate transmission characteristics of waves inside the waveguide. Numerical results are obtained in the paper and compared with theoretical predictions: a good agreement is found.     

Atomistic simulation on the site preference and mechanical properties of Th3Co4+xAl12−x and U3Co4+xAl12−x

An atomistic study is presented on the phase stability, site preference and lattice constants of the actinide intermetallic compounds Th₃Co_4+xAl_12−x and U₃Co_4+xAl_12−x. Calculations are based on a series of interatomic pair potentials related to the actinides and transition metals, which are obtained by a strict lattice inversion method. The lattice constants of Th₃Co_4+xAl_12−x and U₃Co_4+xAl_12−x are calculated for different values of x. The site preference of Co atoms at Al sites is also evaluated and the order is given as 6h, 4f, 2b and 12k for Th₃Co_4+xAl_12−x, and 6h, 4f, 12k and 2b for U₃Co_4+xAl_12−x. In addition, some simple mechanical properties such as the elastic constants and bulk modulus are investigated for the actinide compounds with complex structures.