Extracting the composition of nanocrystals of mechanically alloyed systems using Mössbauer spectroscopy

Abstract

Determining the composition at the nanoscale generally requires the use of experimental techniques such as 3D atom probe or nanoanalysis, which have limited availability, involve high economic cost and, moreover, imply aggressive sample preparations. However, the combination of Mössbauer spectrometry (MS), X-ray diffraction (XRD) and magnetization measurements can supply very detailed information on the average values of composition of tiny elements of the microstructure such as nanocrystals and boundary regions. Unlike nanoscale techniques, those techniques are widely accessible to most of the scientific community and do not require any special sample preparation, especially for powder samples. Two methods are proposed: the first method uses the ratio between the high field contributions to the MS spectra to extract the composition of the nanocrystals and allows us to follow its evolution; the second method uses average values of the hyperfine field and XRD data to study nanocrystalline samples. These procedures have been applied to two FeNb(B) powder samples obtained by mechanical alloying. The proposed procedures can be easily extended to systems containing other isotopes suitable for Mössbauer spectroscopy or to data from nuclear magnetic resonance experiments.Journal of Alloys and Compounds, 610 (2014) 92-99 http://dx.doi.org/10.1016/j.jallcom.2014.04.195 2 IntroductionCompositional and microstructural characterization of materials is a key point to optimize technological properties, to understand the underlying physics and to develop theories and models to go further in Materials Science. This characterization is especially tricky for nanoscale systems, for which the characteristic size to be analyzed can be so small that could apparently be only accessible to nanoprobe techniques (such as high resolution transmission electron microscopy, 3D atom probe, atomic force microscopy, etc.). The presence of irregularities even at such scales implies non simple interpretation of the results. In addition, nanoscale techniques, in general, require costly (economically and in time) sample preparation procedures and limit the explored region to a very small part of the sample (where, artifacts due to the effects of sample preparation might also play a role). Therefore, a very detailed but local information is obtained and it must be extrapolated to the overall system. Unlike these techniques, conventional ones such as X-ray diffraction or Mössbauer spectroscopy can supply average information of a sample with a macroscopic size. These techniques are widely used to identify the phases present in the material and some other structural characteristics such as crystal size, microstrains, lattice parameter, etc. In fact, compositional information can be derived from Mössbauer data but requires further analysis in combination with other experimental techniques. In fact, the capabilities of Mössbauer spectroscopy to analyze nanoscale systems have been pointed out by different authors [1,2,3,4].For magnetic appli...

On the Use of JMAK Theory to Describe Mechanical Amorphization: A Comparison between Experiments, Numerical Solutions and Simulations

“…This technique is clearly more sensitive than X-ray diffraction (XRD) for detecting small fractions of paramagnetic phases in a ferromagnetic matrix and vice versa [26]. The sizes of the remaining crystals were estimated from the area ratio of the interface and core contributions to MS [27]. Numerical solutions and simulations were performed using Matlab scripts (Matlab R2016a, The Mathworks Inc., Natick, MA, USA).…”

Influence of Milling Time on the Homogeneity and Magnetism of a Fe70Zr30 Partially Amorphous Alloy: Distribution of Curie Temperatures

“…57 Fe Mössbauer spectroscopy has been frequently used to follow the compositional evolution of the Fe containing phases present in mechanically alloyed powders [21,30]. In fact, it is known that Mössbauer spectroscopy (MS) is a more sensitive technique than X-ray diffraction for the detection of small fractions of Fe phases when paramagnetic and ferromagnetic phases coexist [15].…”

“…In fact, it is known that Mössbauer spectroscopy (MS) is a more sensitive technique than X-ray diffraction for the detection of small fractions of Fe phases when paramagnetic and ferromagnetic phases coexist [15]. Moreover, MS can provide extensive and valuable information, such as the oxidation state, the coordination mode, and the nature of ligands [31], as well as the composition of the nanocrystals [30]. Finally, the determination of the magnetic ordering temperature allows for determining the coexistence or the absence of different phases in the studied system [32].…”

Evolution of Fe environments and phase composition during mechanical amorphization of Fe70Zr30 and Fe70Nb30 alloys

“…present the advantage of a much better statistics to obtain average values and are experimental techniques accessible to most of the scientific community. In fact, the capability of Mössbauer spectroscopy to analyze nanoscale systems have been pointed out, particularly when combining with other techniques, such as X-ray diffraction [18,19].…”