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INFLUENCE OF ATOMIC SUBSTITUTION ON SHORT RANGE ORDER IN AMORPHOUS
Fe84B16-xCxALLOYS
J. Balogh, I. Dèzsi, B. Fogarassy, L. Grànàssy, D. Nagy, I. Vincze, S. Arajs
To cite this version:
J. Balogh, I. Dèzsi, B. Fogarassy, L. Grànàssy, D. Nagy, et al.. INFLUENCE OF ATOMIC SUB- STITUTION ON SHORT RANGE ORDER IN AMORPHOUS Fe84B16-xCxALLOYS. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-253-C1-254. �10.1051/jphyscol:1980185�. �jpa-00219778�
JOURNAL DE PHYSIQUE Colloque Cl
,
suppl&tnent au n O 1, Tome 41, janvier 1980, page CI-253INFLUENCE OF ATOMIC SUBSTITUTION ON SHORT RANGE ORDER I N AMORPHOUS Fe84B16-xG AUOYS J. Balogh, I. Dezsi, B. 'Fogarassy, L. Granassy, D.L. Nagy, I. Vincze and
+
S. ~ r a j s "Central Research I n s t i t u t e for Physics, Budapest, Hungary.
Solid State Physics Laboratory, Materials Science Center, University of Groningen, Groningen, The -Netherlands
.
Physics Department, Clarkson College, Postdwn, New York, U.S.A.
There is a considerable interest /1,2,3,4/ at present in the amorphous Fe-B-C alloys because of their relatively high room temperature saturation induction which makes the use of these aLloys in po- wer devices more attractive. This improvement in the magnetic properties has been achieved through the
temperature dependence of magnetization which de- creases slowlier in the Fe-B-C than-in Fe-B glasses /2/. Another unusual effect of the carbon addition is the decrease of the thermal stability of these glasses /3/ contrary to the "confusion principlev' according to which the stability of glasses is ex- pected to increase with increased number of alloying elements. The study of the short-range order of these glasses can give important information to our understanding of their interesting and useful phy- sical properties.
In this paper we report the preliminary results of Mossbauer and calorimetric (DSC) measurements on rapid quenched Feg4B1
6-xC,
(0 5 x 2 10) alloys. The Mossbauer data were evaluated with the method of Ref. 5. The crystallization process was followed by differential scanning calorimetry and the crystal- line samples were obtained by appropriate heat treat- ments in the calorimeter.The crystallization takes place in two steps for x = 6, 8 and 10 similarly to the case of pure Feg4B1 /6/. According to the M6ssbauer measurements the first step is a precipitation of a-Fe and a shift in the composition of the remaining glass to the 25 at.% metalloid concentration. There is no substitutional or interstitial boron or carbon in the precipitated or-Fe on the base of the Mossbauer data (i.e. their amount is certainly less than 0.5%).
In the second step this remaining glass transforms into crystalline Fe (B C ) intermetallic compound.
3 1-Y Y
+On leave from the Central Research Institute for Physics, Budapest, Hungary.
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x . 2Fig. 1: Typical room temperature Mossbauer spectra of FegqB16-&x after different annealings:
a) Feg4B16: after t h e first step of crystallization.
The spectrum consists of a-Fe and am. Fe75B25.
b) Feg4B16: after the second step of crystallization, The spectrum consists of a-Fe and cr. Fe3B with the tetragonal structure.
c) Feg4B14C2: after the second crystallization peak.
The spectrum consists of a-Fe, am.
Fe75(Bo. 875C0. 1 2 5 ) ~ ~ and a few percent of cr.
Fe75(B0.875C0.125)25-
d) Fe84B1 4C2: after the third crystallization peak.
The sDectrum consists of a-Fe cr.
Fe75(b0.875C0. lZ5)25 with the orthorhombic struc- ture.
The crystal structure of these compounds is d i f f ~ y e ~ t ,
depending on the carbon content. The Fe3B (y = 0) is isostmctural to the tetragonal Fe3P intermetal- lic compound /7/. The structure has three crystal- lographically inequivalent iron sites (in eqal num- ber), the nearest boron neighbors of which number
2, 3 and 4, respectively. On the other hand, even the ~ e ~ B 6 . 875C0. 125 (i.e. x = 2) campound is iso- structural to the cementite, Fe,;C. In this ortho- - rhambic structure there are two crystallographically
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980185
c1-254 JOURNAL DE PHYSIQUE
order of these glasses is orthorhombic, cementite
J I
0 2 4 6 8 10 x [ a t 0 / ~ 1
Fig. 2: Concentration dependence of the average iron hyperfine field.
inequivalent iron sites which are coordinated by 2
an33 Cnearest neighbours, the relative occupation of these sites is 1:2 /8/. The Wssbauer spectra of this two crystal structures are quite different as it can be seen in Fig. lb and Id. The spectra iden- tified as boron substituted cementite were similar to those presented by Bernas et al. /9/ Electron dif- fraction measurements / 10/ supported the MiSssbauer identifications of the crystalline phases.
For Feg4B1 4C1 and Feg4B1 2C4 thre peaks appear- ed in the DSC curve, the new peak was between the peak corresponding to the a-Fe precipitation and the final crystallization peak of the 25 at. % glass.
This feature is not well understood at present but serious inhomogeneities in the samples can explain it. The presence of such inhomogeneities seems to be supported by in situ electromicroscopic measurements /lo/ where some tetragonal Fe3B was detected in the crystallization process.
The concentration dependence of the average iron hyperfine field is shown in Fig. 2. There is a slight increase in the hyperfine field at room tem- perature with increasing carbon content in agreement with average magnetization measurements /2,3/. The liquid nitrogen temperature values are nearly con- stant, thus the increasing carbon concentration re- sults in a less flat reduced magnetization curve as
it was shown by Hatta and E ~ - /2/ from magnetic measurements (the -Curie femperaturer does increase dramatically).
The short-range order of the Fe75B25 glass was well approximated /11/ with that of the metastable
tetragonal Fe3B compound which played a dominant role in the crystallization of F~,:~B~ glasses (here tetragonal refers for the local neighbourhoods and not for the long-range symmetry of the structure).
If we extrapolate these results for the Fe(BC) sys- tem we had to assume that the chemical short-range
like (again we refer for the local neighbourhoods).
That is the sudden changes in the physical proper- ties of the Fe-B glasses for the carbon substitution are caused not only by chemical effect but an induced change in the short-range order of these glasses. Re- cent EDXD measurement of Egami /4/ shows an indica- tion oi this sup~sed change in the atomic short- range order. The measured difference in the radial distribution function of Fe85B15 and I:egjB9C6 is characteristic for 3 supposed change from tetragonal to orthorhombic in the local order, namely the in- tensity of the second peak has decreased while that of the third peak has increased resulting in a ten- dency of reversing the intensity ratio of the "se- cond splitted peak" /12/. The suposed change in the short-range order for carbon substitution should be reflected in the iron hyperfine field distribution.
At the 25 at.% stoichionetric composition a narro- wing of p(H) is expected due to the shaqer distri- bution of local confi-gurations in the orthorhombic than in the tetragonal structure. This narrowing of p(H) is absent at 16 at.% metalloid camposition which is not surprising since the off-stoichiometry of these glasses will considerably broaden the dis- tribution.
Acknowledgements. - We thank T. KemSny for stimula- ting discussions.
References
/1/ Hatta, S., Egami, T. and Graham, Jr., D.C., IEEE Trans. Magnetics, MAG-14 (1978) 1013.
/2/ Iiatta, S. and Egami, T., J. Pel. Phys., to be published.
/3/ Luborsky, F.E., Becker, J.J. and Liebermann, H.H., to be published.
/4/ Cgami, T., J. Appl. Phys., to be published.
/5/ Vincze, I., Solid State Comun., 25 (1978) 689.
/6/ Kemsny, T.
,
Vincze, I., FogarassyFB. and Arajs, S., Phys. Rev. B (April 1979)./7/ Herold, U. and KEster, U., Z. ?Ietallkde. 69
(19781 326. -
/8/ ~icholson, M.E., A G E Trans., J. Metals 9 (1957) 1.
/9/ Bernas, H., Campbell, I .A. and Fruchart, R., J .
Phys. Chem. Solids 28 (1967) 17. -
/ l a / Cziraki, A.. Foaarassv. B., Balogh, J., Grbtnassy,
L., Kemsny, T. and Vincze, I., Xi. Magyar Elek- tronmikroszk6ps 2s Mikroanalizis Konferencia, Szeged, 1979.
/11/ Vincze, I., Kemsny, T., and Arajs, S., Phys. Rev.
Rev. B, to be published.
/12/ Tegze; M., Faigel, Gy. and Vincze, I., to be pu- blished.
