Structural investigations on an amorphous Se₉₀Te₁₀alloy produced by mechanical alloying using EXAFS, cumulant expansion and RMC simulations

Abstract

We investigated an amorphous Se(90)Te(10) alloy produced by mechanical alloying using two different approaches. First, we used extended x-ray absorption fine structure (EXAFS) spectroscopy and the cumulant expansion method using the Einstein model for the temperature dependence of the cumulants to obtain the cumulants C(*)(1), C(*)(2), and C(*)(3). From these, we found information about the structure of the alloy as well as the thermal and structural disorder, anharmonicity of the effective interatomic pair potentials, thermal expansion of the Se-Se and Se-Te bonds and asymmetry of the partial distribution functions g(Se-Se)(r) and g(Se-Te)(r). The cumulants C(*)(1), C(*)(2), and C(*)(3) also allowed us to reconstruct the g(EXAFS)(ij)(r,T) functions from EXAFS. Then, we made reverse Monte Carlo (RMC) simulations using the total structure factor S(K) obtained from synchrotron x-ray diffraction and the EXAFS oscillations χ(k) on the Se K edge as input data to obtain the g(RMC)(ij)(r) functions. Both methods furnished very similar g(ij)(r) functions, and the structural data obtained from them were also very similar. The results obtained from both methods showed the presence of Se-Te pairs indicating that there is alloying at the atomic level. In addition, we could not find any evidence of the presence of Te clusters in the alloy.

Low-dimensional systems investigated by x-ray absorption spectroscopy: a selection of 2D, 1D and 0D cases

“…An evident problem in the analysis of the EXAFS data coming from 0D systems concerns in the fact that the Debye-Waller factors,  j 2 in eqn , (5), have a double thermal and static nature [817][818][819]. The former follows the standard temperature trend foreseen by the Einstein model [820][821][822][823][824][825][826], the latter is due to a spread in average interatomic distances undergone by the atoms at the surface of the NPs.…”

Structural and thermal investigations of an amorphous GaSe9 alloy using EXAFS, cumulant expansion, and reverse Monte Carlo simulations

“…The algorithm of the standard RMC method is described elsewhere 56,57 and its application to different materials is reported in the literature. 48,[66][67][68][69][70] The idea is to minimize the function…”

“…This result is different from those found for other Se-based alloys, where the heteropolar pair is stronger than the Se-Se pair. For comparison, Kostrzepa et al 70 obtained k E e,Se-Se = 9.2 eV/Å 2 and k E e,Se-Te = 18.2 eV/Å 2 , for a-Se 90 Te 10 , Machado et al 74 found k E e,Se-Se = 10.6 eV/Å 2 and k E e,Se-P = 13 eV/Å 2 , for a-Se 90 P 10 , and, for a-InSe 9 , Machado et al 75 obtained k E e,Se-Se = 7.6 eV/Å 2 and k E e,Se-In = 8.6 eV/Å 2 . The average interatomic distances, that correspond to the first cumulant C 1 , can be seen at Fig.…”