Mössbauer studies of Fe–Cu alloys prepared by electrodeposition

https://doi.org/10.1016/j.jmmm.2003.08.017Get rights and content

Abstract

Metastable FexCu100−x (x=10, 15, 29 and 45) alloys in powder form are prepared using simultaneous electrodeposition of Fe and Cu from a common bath. The alloys are thermally stable at least up to 300°C, after which gradual phase segregation takes place. Mössbauer spectra of the as-prepared samples show a quadrupole doublet with a large line broadening which decreases as the Fe concentration in the alloy is increased. The line broadening further increases as the samples are annealed, passes through a maximum and sharply falls to very small values as the annealing temperature reaches 600°C.

Introduction

There has been long-standing interest in artificially grown metastable alloys from insoluble binary metallic systems as they offer a variety of new properties and applications [1], [2]. Numerous efforts have been undertaken to synthesize Fe–Cu alloy, which has negligible mutual solid solubility at room temperature despite the fact that iron (Z=26) and copper (Z=29) are very near in the periodic table [3]. Nonequilibrium techniques such as ball milling [4], [5], [6], [7], covapor deposition [8], rapid quenching [9], RF sputtering [10], ion-beam mixing [11], etc. have been used to prepare FexCu100−x metastable alloys at almost all compositions. High iron concentration leads to a BCC phase and a low iron concentration to an FCC phase. There is a range in between for which mixed BCC and FCC phases occur. The range of compositions forming BCC or FCC metastable alloy is found to be highly dependent on the preparation method. For ball-milled Fe–Cu alloys, the structure is BCC for iron between 75% and 100%, whereas it is FCC for 0–60% iron. Mixed BCC and FCC phases appear for iron 60–75%. Alloys made by rapid thermal quenching [9] show mixed phase for 19–85% iron concentration. Mixed BCC and FCC phases occur at 40–55% iron for films made by sputtering [10], at 35–60% for thermally evaporated films and at 27–30% for the electrodeposited films [12]. In the FCC phase, the alloy is found to be paramagnetic, whereas in the BCC phase it shows magnetization smaller than what can be expected from a simple dilution law.

Electrodeposition has proved to be a useful technique for preparation of certain kinds of alloys [13]. It has several advantages over other nonequilibrium techniques such as it is simple to assemble and operate and is quite inexpensive. The electrodeposition method has been used by Ueda and Kikuchi [12] to prepare thin films of Fe–Cu alloys. These films show magnetization and structural behavior quite different from what has been found in other techniques. The fact that electrodeposition from a common bath having more than one type of cation forms alloy is also a challenging job to understand from a theoretical point of view. The process of crystallization in electrodeposition is fundamentally different from that of ordinary melting technique in which crystals solidify from the molten state. Unlike rapid quenching or covapor deposition, here the alloying is done at low temperature. Even the local temperature remains low, in contrast to ion-beam mixing or even ball milling, as the mixing here takes place in the electrolytic solution. This would make alloys with considerably less stress-related effects that are generally introduced at higher temperatures.

Our group had demonstrated the potential of electrodeposition in alloy formation by preparing Fe–Ag alloy [13], a very immiscible system and now we demonstrate it in the case of another immiscible system Fe–Cu. Normally, electrodeposition has been used for alloy formation in thin layers like coating on a substrate. We have successfully prepared alloy in the form of powder. This gives an extra benefit that a large amount of sample is made available in a short time so that characterization by various techniques is easy. The objective of the present article is to report the preparation of Fe–Cu alloys by electrodeposition and study of the structural and magnetic properties of the prepared alloys. We have prepared alloys in different elemental compositions and studied them using X-ray fluorescence (XRF) and Mössbauer spectroscopy. The thermal stability is verified by annealing the as-prepared alloys at different temperatures.

Section snippets

Experimental

Four different compositions of alloys were prepared by two-electrode electrodeposition technique from a single bath using a pure platinum plate as the anode and a pure aluminum plate as the cathode. The electrolytic solution was made by dissolving Cu(NO3)23H2O and FeSO47H2O, both 99.99% pure in distilled water. While the concentration of Cu(NO3)23H2O was the same, 20 g/l, that of FeSO47H2O was taken as 5, 10, 20 and 40 g/l for the four different compositions of Fe–Cu alloy. Anode and cathode were

Determination of the composition of the alloys

Because of different conductivities and reduction potentials of iron and copper their rate of deposition from a common bath will be different. Because of this the final composition of the material deposited could be quite different from that taken in the bath. We measured the final composition using an XRF setup. The energy axis of the MCA was calibrated using different pure materials. Ratio of the area under the peak of Fe (Kα+Kβ) and Cu (Kα+Kβ) in the XRF spectrum is used to obtain the

Conclusion

Electrodeposition has been used for the first time to prepare Fe–Cu metastable alloys in powder form with iron concentration up to 45 at%. The alloys are formed in single phase but the nearest neighbor configurations have distribution as expected for a solid solution. This causes a line broadening in the quadrupole-split Mössbauer spectrum. The more crucial factor responsible for line broadening seems to be defect distribution and oxygen/hydrogen incorporation during electrodeposition and

Acknowledgments

This work was financially supported by DST, New Delhi.

References (16)

  • T. Ambrose et al.

    J. Magn. Magn. Matter.

    (1993)
  • K. Sumiyama et al.

    J. Magn. Magn. Matter.

    (1983)
  • M.K. Roy et al.

    J. Alloys Compounds

    (2002)
  • E.F. Kneller

    J. Appl. Phys.

    (1962)
  • F. Kazar et al.

    J. Appl. Phys.

    (1979)
  • Ortrud. Kubaschewski, Iron-Binary Phase Diagrams, Springer, Berlin, Heidelberg, New York,...
  • G. Mazzone et al.

    Phys. Rev. B

    (1996)
  • E. Ma et al.

    J. Appl. Phys.

    (1993)
There are more references available in the full text version of this article.

Cited by (0)

View full text