Local atomic arrangement in mechanosynthesized Co x Fe1−x−y Ni y alloys studied by Mössbauer spectroscopy

Tomasz Pikula

doi:10.1007/s00339-014-8582-1

Abstract

Mechanosynthesized Co x Fe1−x−y Ni y alloys were examined using X-ray diffraction (XRD) and Mössbauer spectroscopy. In order to explain the shape of hyperfine magnetic field (HMF) distributions for the alloys, a local environment model based on a multinomial distribution was proposed. The model was in agreement with the XRD data and confirmed that the studied alloys were disordered solid solutions. It was successfully applied to describe the samples with bcc and fcc crystalline lattice type within the relatively broad range of components concentration. The results showed that the change of the crystalline lattice type does not cause an abrupt change of the HMF value. Moreover, a mean number of unpaired spins for the first coordination sphere may be used as a parameter to describe the HMF value experienced by 57Fe nucleus. Finally, a set of the most probable atomic configurations and their corresponding contributions to the HMF distribution were obtained.

Highlights

It is well known that many of the physical properties of alloys depend on local atomic arrangement of atoms in crystalline lattice
Simple model based on multinomial fcc to bcc does not cause a rapid change of the hyperfine magnetic field (HMF) value
The parameter which may be used to describe the value of HMF sensed by 57Fe probe is the mean number of unpaired spins, s, for the atom in the first coordination shell

Summary

Introduction

It is well known that many of the physical properties of alloys depend on local atomic arrangement of atoms in crystalline lattice. During the past few decades, many efforts were made to examine the type of atomic ordering in a variety of materials. When considering the chemical ordering of atoms, three types of alloys can be distinguished: (1) disordered systems, (2) alloys with a short-range order (SRO) and (3) alloys with a long-range order (LRO). The disordered state means that atoms of individual components are randomly located at lattice sites, and the probability of finding a given type of atom in a particular crystallographic position is given by the chemical concentration of such element. The term short-range order is used to describe the preference of certain types of atoms to reside near each other. The long-range order is related to the development of a certain atomic pattern through the whole crystal [3]

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