Structural transformations and thermal stability of RhGe synthesized under high temperature and pressure.

Here, we study B20-type RhGe, a representative of a class of non-centrosymmetric monosilicides and monogermanides, which possess unique topological and magnetic properties important for many possible applications. The stability and phase transitions of the non-equilibrium B20-RhGe phase that can only be obtained under high pressure, are investigated theoretically usingab initiocalculations and experimentally by means of differential scanning calorimetry. For RhGe and, for comparison, for its analogue RhSi, we conducted an evolutionary search for low-energy polymorphic modifications at zero temperature and then performed simulations of their behavior at finite temperatures. The (P,T) conditions of stability for the found polymorphs are determined. Our calorimetric studies on high-pressure-synthesized RhGe samples allowed us to reveal peculiarities in thermal stability and heating-induced phase transformations. X-ray diffraction analysis and microstructure analysis of the samples were carried out before and after the heating. We also determined the specific heat from calorimetric measurements and compared the results with our calculations in the quasi-harmonic approximation.

Is icosahedral short-range order presented in supercooled transition metals?

Supercooled transition metals are characterized by the absence of long-range order and the presence of a specific short-range order in the arrangement of atoms. So, the presence of shoulders and broadenings at the second maximum in the experimentally measured quantity-in the static structure factorS(k)-is usually interpreted as a manifestation of the icosahedral (ideal or distorted) short-range order (ISRO-Icosahedral Short-Range Order). Icosahedral short-range order is a structure with fivefold symmetry in the arrangement of atoms, which can lead to the possibility of achieving deep supercooling. In this work, we study the local structural features of equilibrium and supercooled nickel melts under various cooling protocols (γ∈1010,1014 K s-1) in order to clarify the mechanism of formation of the icosahedral short-range order in pure transition metals. Comprehensive studies of the properties of nickel melts were carried out using experiments on x-ray diffraction, large-scale molecular dynamics (MD) simulations with subsequent structural and cluster analysis. A good agreement was found between the results of x-ray diffraction data and the MD simulations results for an equilibrium nickel melt. It was found that the nickel melt is characterized by a short-range order, formed by fragments of icosahedra and distorted icosahedral clusters. It was revealed that the 'liquid-crystal' phase transition in nickel is accompanied by the transformation of distorted icosahedral clusters into clusters with thefcc/hcp-symmetry. It is shown that, in contrast to the Voronoi tessellation method, the cluster analysis method based on the (q4,q6) rotational invariants does not allow sufficiently correct identification of the distorted icosahedral short-range order in metal melts.

Effect of copper concentration on the structure and properties of Al-Cu-Fe and Al-Cu-Ni melts.

We address a relationship between properties of liquid and solid states by comparing structural characteristics and viscosity in Al-Cu-Fe and Al-Cu-Ni melts. The former system forms an equilibrium quasicrystalline phase but the latter does not. We show that the concentration behavior of the viscosity, melting temperature and characteristics of the chemical short-range order correlate with each other. The main structural differences between the melts are related to the peculiarities of their electronic structure, which is the same for liquid and solid states near the melting temperature.

Galactic cosmic ray flux simulation and prediction.

A dynamic galactic cosmic ray model is proposed to quantitatively describe the z=1-28 ions and electrons of E=10-10(5) MeV/nucleon and their particle flux variations around the Earth's orbit and beyond the Earth's magnetosphere due to diverse large-scale variations of solar activity factors. The variations of large-scale heliospheric magnetic fields and the galactic cosmic ray flux variation time delays relative to solar activity variations are simulated. The lag characteristics and sunspot number predictions having been determined in detail, the model can be used to predict galactic cosmic ray flux levels.

An analytical model, describing dynamics of galactic cosmic ray heavy particles.

The present paper analyses the problems of modeling galactic cosmic ray particle fluxes. A model representation which enables the particle energy spectra for large-scale solar activity induced modulations to be calculated is described.

Cosmic ray particles with different LET values under various thicknesses of shielding in low altitude orbits: calculations and Cosmos-2044 measurements.

Fluxes of cosmic ray particles with different LET values were measured on board the Cosmos-2044 biosatellite under various thicknesses of shielding by stacks of CR-39 and nitrocellulose plastic nuclear track detectors (mounted outside the satellite). The component composition of the particles detected under shieldings of 0.1-2.5 g cm-2 is verified by comparing experimental data with the results of model simulations of the fluxes of galactic cosmic ray particles and of radiation belt protons.