805 research outputs found
Structure of Liquid Antimony by Neutron Diffraction
Neutron diffraction patterns from liquid antimony have been obtained at 660 and 800℃. The structure factors are nearly independent of temperature. Comparing the results with the structure of liquid bismuth and the hard sphere model the existence of two structure types in liquid antimony previously indicated seems to be ambiguous. The electrical resistivity was calculated using Ziman\u27s theory and compared with experimental data. From this in the case of liquid antimony the invalidity of the Born approximation in Ziman\u27s theory was found
Structural Study of an Amorphous Pd_<80>-Si_<20> Alloy by X-Ray Fourier Analysis
The structure of an amorphous Pd_-Si_ alloy obtained by rapid quenching from the liquid state has been studied by X-ray diffraction . After calculating the interference function by means of the Fourier analysis, the atomic radial distribution function is obtained from which interatomic distance and coordination number are estimated. Comparing the result with that in the liquid state it is found that the general feature of the structure in the amorphous state is quite similar to that in the liquid state. Besides, the sample aged at 180℃ for 300 min is examined by the same procedures
Structure of Amorphous Fe_<80>-P_<13>-C_7 by X-Ray Diffraction
X-ray diffraction patterns have been obtained from Fe_-P_-C_7 alloy in both amorphous and liquid states. Using the common Fourier analysis, the atomic radial distribution function was evaluated from which interatomic distance and coordination number were obtained. The essential feature of the structure in the amorphous state was similar to that in the liquid state. The crystallization process of this alloy during isothermal aging at 330℃ was also studied by the same procedures. The results indicated that the initial amorphous structure changes to a second amorphous structure, which in turn, transforms to the stable crystalline phase. This crystallization product was single phase of bcc structure (a_0=2.864A). By means of the Fourier analysis, these results led to the conclusion that the initial amorphous structure re-arranges to relax the stress or anisotropic configuration of atoms arising from the rapid quenching and subsequently the crystallization of this alloy occurs by a nucleation and growth mechanism during isothermal aging
Potentiometric determination of the gibbs energies of formation of SrZrO and BaZrO
The Gibbs free energies of formation of strontium and barium zirconates have been determined in the temperature range 960 to 1210 K using electrochemical cells incorporating the respective alkaline-earth fluoride single crystals as solid electrolytes. Pure strontium and barium monoxides were used in the reference electrodes. During measurements on barium zirconate, the oxygen partial pressure in the gas phase over the electrodes was maintained at a low value of 18.7 Pa to minimize the solubility of barium peroxide in the monoxide phase. Strontium zirconate was found to undergo a phase transition from orthorhombic perovskite (o) with space group Cmcm; D172h to tetragonal perovskite (t) having the space group 14/mcm;D 184h at 1123 (±10) K. Barium zirconate does not appear to undergo a phase transition in the temperature range of measurement. It has the cubic perovskite (c) structure. The standard free energies of formation of the zirconates from their component binary oxides AO (A = Sr, Ba) with rock salt (rs) and ZrO2 with monoclinic (m) structures can be expressed by the following relations: SrO (rs) + ZrO2 (m) → SrZrO3 (o) ΔG± = -74,880 - 14.2T (±1200) J mol-1 SrO (rs) + ZrO2 (m) → SrZrO3 (t) ΔG±= -73,645 - 15.37T (±200) J mol-1 BaO (rs) + ZrO2 (m) → BaZrO4 (c) ΔG± = -127,760-1.79T (±1250) J mol-1 The results of this study are in reasonable agreement with calorimetric measurements reported in the literature. Systematic trends in the stability of alkaline-earth zirconates having the stoichiometry AZrO3 are discussed
Signature of nearly icosahedral structures in liquid and supercooled liquid Copper
A growing body of experiments display indirect evidence of icosahedral
structures in supercooled liquid metals. Computer simulations provide more
direct evidence but generally rely on approximate interatomic potentials of
unproven accuracy. We use first-principles molecular dynamics simulations to
generate realistic atomic configurations, providing structural detail not
directly available from experiment, based on interatomic forces that are more
reliable than conventional simulations. We analyze liquid copper, for which
recent experimental results are available for comparison, to quantify the
degree of local icosahedral and polytetrahedral order
Electron-ion and ion-ion potentials for modeling warm-dense-matter: applications to laser-heated or shock-compressed Al and Si
The pair-interactions U_{ij}(r) determine the thermodynamics and linear
transport properties of matter via the pair-distribution functions (PDFs),
i.e., g_{ij}(r). Great simplicity is achieved if U_{ij}(r) could be directly
used to predict material properties via classical simulations, avoiding
many-body wavefunctions. Warm dense matter (WDM) is encountered in
quasi-equilibria where the electron temperature differs from the ion
temperature T_i, as in laser-heated or in shock-compressed matter. The electron
PDFs g_{ee}(r) as perturbed by the ions are used to evaluate fully non-local
exchange-correlation corrections to the free energy, using Hydrogen as an
example. Electron-ion potentials for ions with a bound core are discussed with
Al and Si as examples, for WDM with T_e \ne T_i, and valid for times shorter
than the electron-ion relaxation time. In some cases the potentials develop
attractive regions, and then become repulsive and `Yukawa-like' for higher
. These results clarify the origin of initial phonon-hardening and rapid
release. Pair-potentials for shock-heated WDM show that phonon hardening would
not occur in most such systems. Defining meaningful quasi-equilibrium static
transport coefficients consistent with the dynamic values is addressed. There
seems to be no meaningful `static conductivity' obtainable by extrapolating
experimental or theoretical \sigma(\omega, T_i, T_e) to \omega \to 0, unless
T_i \to T_e as well. Illustrative calculations of quasi-static resistivities
R(T_i,T_e) of laser-heated as well as shock-heated Aluminum and Silicon are
presented using our pseudopotentials, pair-potentials and classical integral
equations. The quasi-static resistivities display clear differences in their
temperature evolutions, but are not the strict \omega \to 0 limits of the
dynamic values.Comment: 12 pages, 6 figues, Latex file
Partial Structure Factors of Liquid Na-K and Al-Mg Alloys(Physics)
Three partial structure factors S_(Q) have been evaluated from the scattered X-ray intensities of liquid Na-K and Al-Mg alloys assuming that the S_(Q) are independent of the relative abundance of the respective elements in the alloys. The functions S_(Q) and S_(Q) and the reduced radial distribution functions G_(r) and G_(r) obtained in this work are very similar to those observed in the respective pure liquid metals. In both cases, S_(Q) and G_(r) have maxima which lie in between those of the pure elements. From these results, liquid Na-K and Al-Mg alloys are interpreted as random mixing fluids. A comparison between the partial structure factors obtained in this work and those calculated from the hard sphere model was made. Adequate agreement was obtained on the low angle side of the first peak, but agreement on the whole pattern is not necessarily found. The electrical resistivity was calculated using Faber-Ziman\u27s theory and compared with experimental data
Sulphur potential measurements with a two-phase sulphideoxide electrolyte
The open circuit potentials of the galvanic cell,Pt
(or Au)|(Ar + H2S + H2)'||CaS +
ZrO2(CaO)|| (Ar + H2S+
H2)"|Pt (or Au) has been measured in the
temperature range 1000 to 1660 K and
PH2S:PH 2 ratios
from 1.73×10-5 to 2.65×10-1.
The solid electrolyte consists of a dispersion of calcium
sulphide in a matrix of calcia-stabilized zirconia. The
surface of the electrolyte is coated with a thin layer of
calcium sulphide to prevent the formation of water vapour by
reaction of hydrogen sulphide with calcium oxide or zirconia
present in the electrolyte. The use of a point electrode with
a catalytically active tip was necessary to obtain steady
emfs. At low temperatures and high sulphur potentials the
emfs agreed with the Nernst equation. Deviations were
observed at high temperatures and low sulphur potentials,
probably due to the onset of significant electronic
conduction in the oxide matrix of the electrolyte. The values
of oxygen and sulphur potentials at which the electronic
conductivity is equal to ionic conductivity in the two-phase
electrolyte have been evaluated from the emf response of the
cell. The sulphide-oxide electrolyte is unsuitable for
sulphur potential measurements in atmospheres with high
oxygen potentials, where oxidation of calcium sulphide may be
expected
Improved modelling of liquid GeSe: the impact of the exchange-correlation functional
The structural properties of liquid GeSe are studied by using
first-principles molecular dynamics in conjuncton with the Becke, Lee, Yang and
Parr (BLYP) generalized gradient approximation for the exchange and correlation
energy. The results on partial pair correlation functions, coordination
numbers, bond angle distributions and partial structure factors are compared
with available experimental data and with previous first-principle molecular
dynamics results obtained within the Perdew and Wang (PW) generalized gradient
approximation for the exchange and correlation energy. We found that the BLYP
approach substantially improves upon the PW one in the case of the short-range
properties. In particular, the GeGe pair correlation function takes a more
structured profile that includes a marked first peak due to homopolar bonds, a
first maximum exhibiting a clear shoulder and a deep minimum, all these
features being absent in the previous PW results. Overall, the amount of
tetrahedral order is significantly increased, in spite of a larger number of
GeGe homopolar connections. Due to the smaller number of miscoordinations,
diffusion coefficients obtained by the present BLYP calculation are smaller by
at least one order of magnitude than in the PW case.Comment: 6 figure
Chemical order and crystallographic texture of FePd:Cu thin alloy films
FePd thin films have been recently considered as promising material for
high-density magnetic storage devices. However, it is necessary to find a
proper method of fabrication for the (001)-textured and chemically well-ordered
alloy. In this paper, we present the detailed investigations of lattice
parameters, chemical order degree, grain sizes and crystallographic texture,
carried out on FePd alloys with 10 at.% of Cu addition. The initial [Cu(0.2
nm)/Fe(0.9 nm)/Pd(1.1 nm)]x5 multilayers were thermally evaporated in an
ultra-high vacuum on MgO(100), Si(100), Si(111) and Si(100) covered by 100 nm
thick layer of amorphous SiO2. In order to obtain homogeneous FePd:Cu alloy,
the multilayers were annealed in two different ways. First, the samples were
rapidly annealed in nitrogen atmosphere at 600oC for 90 seconds. Next, the long
annealing in a high vacuum for 1 hour at 700oC was done. This paper focuses on
quantitative investigations of the chemical order degree and crystallographic
texture of ternary FePd:Cu alloys deposited on four different substrates. In
order to obtain both quantities we have taken a novel approach to consider the
problem of dopant atoms located in the FePd structure. The studies of the
structure were done using X-Ray Diffraction (XRD) performed with synchrotron
radiation and pole figures measurements. We have found that the addition of Cu
changes the FePd lattice parameters and lattice distortion. We have also shown,
that using different substrates it is possible to obtain a FePd:Cu alloy with
different chemical order and texture. Moreover, it was observed that texture
category is substrate dependent
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