Brand, R.A.

Ghafari, M.

Gronert, H.-W

Güntherodt, H.-J

Keune, W.

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Zeitschrift fur Physikalische Chemie Neue Folge, Bd. 157, S. 121 -125 (1988)© by R. Oldenbourg Verlag, Munchen 1988-0044-3336/88 $3.00 + 0.00Quadrupole Distributions of the New AmorphousSystem a-Sc3Fe*R.A. Brand, M. Ghafari, W. Keune,Laboratorium fur Angewandte Physik, Universitat Duisburg,D-4100 Duisburg, FRG.H.-J. GiintherodtInstitut fur Physik, Universitat Basel, Basel, SwitzerlandH.-W. GronertLaboratorium fur Tieftemperaturphysik, Universitat Duisburg,D-4100 Duisburg, FRG.AbstractAmorphous Sc-rich FeSc alloys have been prepared byquenching from the melt. The quadrupole splitting distribu-tions for amorphous Sc3Fe were determined from Mossbauerspectra: the zero-field distribution has a Gaussian form.The analysis of Mossbauer spectra taken in applied magneticfield show that both positive and negative electrical fieldgradients (EFG) are present. The crystallization process hasalso been investigated. Heat treatment of the amorphous al-loys causes crystallization first into a metastable, andthen into stable phases.IntroductionRecently the formation of amorphous (a-) Fe-rich alloysFei-iSci over the range x = 0.09 to 0.11 by single rollerquenching has been reported /l/. Also for Sc-rich FeSc, themajor requirments of glass formation i.e. low lying meltingpoint and differing atomic radii are satisfied. (The phase* Presented at the Sixth International Conference on Liquid and Amorphous Metals,Garmisch-Partenkirchen, FRG, August 24 to 29, 1986.Brought to you by | Universitaetsbibliothek BaselAuthenticatedDownload Date | 7/11/17 11:24 AM122 Brand et al.diagram of FeSc shows a low lying eutectic at about x = 0.8./2/) Over the composition range x = 0.75 to 0.80, it wasfound possible to produce amorphous alloys by rapid quen-ching from the melt. In the present work we report onMossbauer quadrupole splitting (QS) measurements on amor-phous and crystallized ScjFe alloys.Experimentala-ScsFe samples were prepared by splat-cooling withlevitation melting using a vaccum better than 5*10-5 Torr.The resulting splats of * 45 urn thickness and 3 cm diameterwere amorphous as indicated by the lack of crystalline peaksin x-ray diffraction. The Fe and Sc used to make the alloyswere of 99.99 % purity. In order to investigate the crystal-lization behaviour, the samples were heated in sealed quartztubes (< 10"4 Torr). Mossbauer measurements were performedwith a 10 mCi 57 Co in Rh source.Results and DiscussionFig.1 shows (a) the Mossbauer spectrum and (b) corres-ponding quadrupole splitting distribution P(QS) for a-Sc3Feat T = 4.2 K in zero field (I). The P(QS) was determinedusing the LeCaer and Dubois /3/ program. Good fits to theasymmetrical spectrum were obtained by assuming a linearrelation between QS and the isomer shift (IS) as suggestedfrom the results for Fe-rich FeSc alloys /l/:IS = -0.06 QS-0.1.The average quadrupole splitting (<QS> = 0.6 mm/s) ist nottoo different from that found for amorphous Zr-rich ZrFe(0.52 mm/s) /4/ and ZrNi (0.51 mm/s) /5/ alloys, but theform of P(QS) is different. The P(QS) found from the histo-gram can be described as a normal distribution of the form:P(QS) = (l/(2*)*o)exp-((QS-<QS>)/(2o* ))with a = 0.25 mm/s and <QS> = 0.60 mm/s. Deviations from theBrought to you by | Universitaetsbibliothek BaselAuthenticatedDownload Date | 7/11/17 11:24 AMQuadrupole Distributions of a-Sc3Fe 123normal distribution were found for small QS. Informationabout the sign of EFG and thus about the local symmetry ofthe Fe sites in SosFe can be obtained by Mossbauer measure-ments in external magnetic field. For the analysis of suchspectra we assumed P(QS) to be a superposition of two normaldistributions of the form:P(QS) = (l-P)(l/(2K)*a)exp-(<QS+<QS>)/(2aM) +P<l/(2*)*a)exp-((QS-<QS>)/(2a* ))with 0 < P < 1, and a single value of the asymmetry parame-ter r^. Spectra have been simulated using this form with theBlaes et al. /6/ program for the line shape with mixed mag-netic dipole and electric quadrupole interactions for anisotropic EFG texture. A first-approximation fit was foundfor P = 0.4 and rj = 0, shown as (II) in Fig. 1(a) and (b).Thus both positive and negative EFG are present. Presentlywe are working on improving these results to obtain moredetailed information.The crystallization temperature determined from DSC(differential scanning calorimetry) measurements with a hea-ting rate of 20 K/min was found to be T = 782 K. Crystal-lization takes place first by the formation of a metastablephase whose structure is sensitive to the condition of heattreatment. Fig. 2(a) shows a typical spectrum (I) from acrystallized sample together with the distribution P(QS),Fig. 2(b), where we find <QS> = 0.28 mm/s. An analysis ofthe x-ray diffraction pattern shows several phases, but al-lows only a clear identification of hexagonal Sc precipi-tates. In the stable crystalline state, two precipitateswith the following lattice parameters were obtained:(1) hexagonal Sc with a = 0.33 nm, c = 0.52 nm, and (2) theintermetallic compound Fe2Sc (C14 type) with a = 0.49 nm,b = 0.78 nm. Usually the spectrum of FejSc consists of thesuperposition of two sextets with relative intensity 3:1/7/, but that of the Fe2Sc obtained from crystallizing SC3FeBrought to you by | Universitaetsbibliothek BaselAuthenticatedDownload Date | 7/11/17 11:24 AM124 Brand et al.is much different: Fig. 2(a), spectrum (II). Such differen-ces can be expected from deviations from stoichiometric com-position as is indicated by the difference in lattice para-meter b from that reported in /7/.ConclusionWe have shown that the Sc-rich ScFe alloys can be preparedin an amorphous state by quenching from the melt. AmorphousSojFe has been studied by 57Fe-M6ssbauer spectroscopy andit was found that the form of P(QS) ist different from thatfound in other similar amorphous metal-metal alloys (ZrNi,ZrFe). The distribution P(QS) was found to be Gaussian, andfrom in-field measurements, both signs of QS were found tobe present. The crystallization process was followed by DSC,Mossbauer and x-ray studies. An intermediate metastablephase and stable crystalline phases were found. The end-product of crystallization consists of hexagonal Sc phaseand a second intermetallic compound.This work was supported by the DFG SFB-166 Duisburg-Bochum.We thank Dr. N. Blaes for a copy of his program, Ing. P.Reimann for sample preparation, and Dip. Ing. U. von Horstenfor help in the Mossbauer measurements.References/l/ Day R.K., Dunlop J.B., Foley CP., Ghafari M. , Pask H.,Solid State Commun. 56, 843 (1985)./2/ Kubaschenski O., Iron Phase Diagrams, Berlin, SpringerVerlag, 1982./3/ LeCaer G., Dubois J.M., J. Phys E 12, 1083 (1979)./4/ Ghafari M., Gonser U., Wagner H.G., Naka M., Nucl.Instrum. Methods 199, 197 (1982)./5/ Ghafari M., Thesis Universitat Saarbrucken 1982./6/ Blaes N., Fischer H., Gonser U., Nucl. Instrum.Methods, B9, 201 (1985)./7/ Smit P.H., Buschow K.H.J., Phys. Rev. B 21_, 3839(1980).Brought to you by | Universitaetsbibliothek BaselAuthenticatedDownload Date | 7/11/17 11:24 AMQuadrupole Distributions of a-Sc3Fe 125UJu_Lt_UJ-2 0 2VELOCITY (mm/e)-1 0 1QS (mm/s)Figure 1. (a) Spectra and (b) Quadrupole distributionsfor a-ScaFe at T = 4.2 K. (I): Zero field and (II):H«xt = 5 T, perpendicular to gamma ray. In (b-I), theresults (solid line) is compaired to the normaldistribution (shown as circles).oLULLLU-1 0 1VELOCITY (mm/c)0 0.3QS (mm/s) uaaAa'11-5 0 5VELOCITY (mm/s)Figure 2. (a) Spectra and (b) Quadrupole distributionfor crystallized Sc3Fe heated to (I): 550 C for ca. 1hour; (metastable state) measured at RT, and (II): 650C for ca. 1 hour; (stable state) measured at T = 4.2 K(magnetic).Brought to you by | Universitaetsbibliothek BaselAuthenticatedDownload Date | 7/11/17 11:24 AM

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