The metastable states of some amorphous FeB alloys

Journal of Non-Crystalline Solids 163 (1993) 49-58 North-Holland

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{

JouRNAL or ~ ~ ~LII~

The metastable states of some amorphous F e - B alloys A. Szasz ", M.A. Aysawy a, Z. D a n k h a z i ~, L. K e r t e s z ~, H. Miiller b a n d H. K i r c h m a y r ~ Department of Atomic Physics, Eotuos Uniuersity, Muzeum krt. 6-8, H-1088 Budapest, Hungary b Institute of Experimental Physics, Technische Uniuersitiit Wien, Wiedner Haupstr. 8, A-1040 Vienna, Austria Received 4 September 1992 Revised manuscript received 29 March 1993

The interdependence of the electronic and thermal properties and their effect on the stability of some Fes6.5_xTMxB~3 5 (TM is transition metal, 0 _< x < 5) alloys is investigated. Differential thermoanalysis and soft X-ray fluorescent spectroscopy were used to measure the thermodynamic phase changes and the partial electronic density of states, respectively. A general role of the electronic effects on the thermal stability is suggested from the trend of the measured data. It is concluded that the thermal stability is effectively controlled by the actual electronic structure of the alloy.

I. Introduction

The problem of stability of alloys and their metastable states, like the amorphous phases, has been widely investigated [1]. Metastability is a fundamental property of crystalline and amorphous alloys [2], having some technical applications [3] as well. Originating from Hume-Rothery's pioneering and synthesizing works [4,5], we enumerate the factors [6] affecting stability: (i) chemical and electrochemical [7,8]; (ii) geometrical [9,10]; (iii) electronic (for example number of electrons per atom), and band-structure effect [11,12,13,14]. Electronic effects, a priori, have a role in every factor listed above: the chemical and electrochemical effects depend on chemical bonds [15];

Correspondence to: Dr A. Szasz, Department of Atomic Physics, Eotvos University, Muzeum krt. 6-8, H-1088 Budapest, Hungary. Tel: +36-1 266 9833. Telefax: +36-1 266 7253.

the geometrical (size) effects are determined by the electronic structure of the atoms [15]. Every property of a system, connected with the electronic states, in principle, can be calculated from first principles. Despite this fundamental importance of the electronic states, there are (to our knowledge), no wide-range investigations devoted to the electronic stability problem. This paucity is because the measurements are dominated by the primary observations; from the point of view of experiments, the electronic effects at the phase transitions (due to its complications) are not studied in detail. Our aim in the present paper is to study the electronic stability effects. For these purposes, various F e - B - T M (TM is transition metal) based amorphous alloys are studied as model systems. The general stability of the state was determined by thermodynamic measurements (differential thermoanalysis (DTA)), while the study of electronic band structure and its effects was carried out by soft X-ray fluorescent spectroscopy (SXFS). The comparison between these two experiments gives a chance to study the correlation between

0t)22-3093/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved

A. Szasz et al. / The metastable states of some amorphous F e - B alloys

50

the experimental electronic band structure and thermal stability.

I, are units

2. Experimental The D T A measurements were made with a home-made high-sensitivity system [16]. The sensitivity in the 150-500°C region was 0.005°C. The heating rate was 10°C/min in every investigated case. The measuring circumstances such as the electronic setup of the experiment were kept constant. The SXFS measurements were made with SARF-1 (Burevestnik) equipment, described elsewhere [17]. The actual pressure during the measurements was 3 × 10 -5 Pa. The sample holder was cooled by a cold finger, which was cooled inside by running water, to avoid thermal effects during the SXFS measurements. The X-ray tube was thermally well isolated from the sample holder; so, we assumed that the samples were not above room temperature. The energy resolutions were 0.1 and 0.3 eV on B K s and Fe L 2 , 3 , respectively. These spectra provide information about the p (for B) and (s + d) (for Fe) partial density of electronic states. The Fermi energy (the highest energy of occupied electronic states is approximately the half-height of the edge at the high-energy part of the spectra. Samples were made by melt-spinning from liquids [18] of a well controlled mixture of high purity F e - B master alloy and another transition metal (TM) [19]. The parameters of the samples under investigation are collected in table 1. The elemental composition was measured after the

Table 1 Collection of the measured All~

No.

alloys ( F e l 0 0 x _ r T M x B 1 3 . 5 )

x(%) Ti

1

5

2 3 4 5 6

. .

Cr

Mo

Ta

Au

3

1 3

--

5 . .

3 . .

. .

--

. . . . . . . . . . . . . .

I-,eV

Fig. 1. B K,~ s p e c t r a o f s o m e Fes6.5 x T M x B l 3 . 5 ( T M is t r a n s i t i o n m e t a l f r o m 3 d - p e r i o d , 1 < x < 5) a m o r p h o u s alloys. ( a ) F e A u 1 B 1 3 . 5 , (b) F e M o 3 B l 3 . 5 , (c) FeCrsB13.5, ( d ) F e T a 3 B 1 3 . 5 , (e) FeTisBl3.5.

sample-making [20]. All of the samples were originally X-ray amorphous.

3. Results At first we measured the binary Fe86.5B19.5 system for reference. SXFS spectra agree well with published data both for boron and iron components [21,22]. To our knowledge, the electronic structure of F e - B - T M ternary systems has not been investigated. A series of the SXFS measurements for samples alloyed with TMs are shown in fig. 1. No large changes were observed by the TM alloying, but a shift of the peak positions as well as changes in the half-band width (HBW) was detected, greater than experimental energy resolution, and was definitely greater than the statistical error of v~-, where N is the actual count number.

A. Szasz et al. / The metastable states of some amorphous Fe-B alloys \ 8.50

\l

Ti5 \ \

7.50

col bond contribution to the electronic structure, appearing in a hybridization of the metalloid pband with the metal d-band. This effect is observed in the correlation of the position of the peaks with the HBW [21] for the different samples (fig. 2). The D T A measurements show well known features [24]. The first peak corresponds to the precipitation of the components in excess of the stable ( F e - T M ) 3 B compound [25]. (Components whose concentration is over of the chemically stable Fe3B-type compound are called 'excess' in the following.) The second peak is a consequence of an amorphous-crystalline phase transition [26]. A series of D T A curves for the different samples is shown in fig. 3. The peak produced by the precipitation does not depend on the alloying elements (fig. 4).

Au3

\

•

\ Au3 \

ref. T

\ \

>

\ 650

Cr5

~Mo3

m T

\

5.50

4.5(

183

51

164 Peak position (eV)

Fig. 2. The correlation between the peak positions and halfbandwidth (HBW) for the investigated samples. The dashed line is only a guide for the eye. The labels of the points correspond to the TM alloying element.

4. Discussion

The asymmetrical peak has a long low-energy tail with a small shoulder and a gradual descent finished in an edge in the high-energy part of spectra. These features are characteristic of covalent bonding [22,23]. There is a significant chemi-

The binary Fel_yBy alloys have been discussed in detail in the relevant literature [27,28]. The F e - B - T M phases have some peculiarities. The precipitation of elements in excess of

~8~

S22

546

Fig. 3. Series of DTA curves of different Feloo_x_yTMxBy (0< x_<5; y =13.5) alloys. (a) FeCrsBi3.5, (b) FeAu3B13.5, (c) FeMo3Bx3.5, (d) FeTa3B13.5.

52

A. Szasz et al.

/ The metastable states of some amorphous Fe-B alloys

,,oi 450-

&301

----Q

O-Q----I

g - - --

Cr5Ta3Mo3

Ti5

Au~ e/a

Z

7,2

7,3

Fig. 4. Temperature of a-Fe precipitation versus electron/ atom ratio, e / a , does not change in the limits of the experimental error. The dashed line is only a,guide for the eye. The labels of the points correspond to the TM alloying element.

the formula of (Fel_zTMz)3B is not affected by the TM; precipitation of tx-Fe takes over. On the other hand, the effects of TM content is observed in the crystallization temperature, Tc~yst, and the area under the peak in the D T A data which is due to the crystallization process (transition heat, AQ). The measured values of Tc~yst and AQ are well correlated (fig. 5). Let us describe and discuss the observed features of the dilute ( F e - B ) - T M alloys using the well known electron/atom ratio, e/a [30], which is recognized as an important factor which determines the alloy stability [6,29,31,32,33]. The value

of e/a was calculated using the nearly free approximation of the electronic band structure, primarily introduced for the Hume-Rothery alloys [31]. The e/a, of course, represents an average; it is a thermodynamic-b.'ke macroscopic parameter. In this sense, the e/a will have a functional dependence on the D T A parameters and has the same general thermodynamic meaning as do the D T A data. By the generalization of the Hume-Rothery rules, the simplest electronic stabilization model was formulated for amorphous alloys by Nagel and Tauc [34], expecting a distinguishable pseudo-gap in the density of electronic states (DOS) at the Fermi energy, E F. However, there are some trivial contradictions [35,36] with the Nagel-Tauc stabilization criterion: the E F in several amorphous ternary FeB-based alloys is not situated near the minimum of the DOS. This in fact appears in contradiction to the stabilization role of the electronic structure in these alloys, so we focus our attention to its details. The local stability ('local' means a stability that is not the available deepest energy minimum, but a minimum with an energy barrier from the deeper minima; this barrier fixes the state in the local stability) of the alloy can be determined by

2500C

\

2000C

\ \

o~ 1 5 0 . 0 0

E

\

-x,

uo 10000

\

\ D

"x. \ \

5000

000

450 oo

500.00

55O'oo Tcryst

60o'0

(~C)

Fig. 5. Crystallization temperature, Tcryst versus crystallization heat, AQ. The dashed line is only a guide for the eye. The labels of the points corresponds to the TM alloying element.

53

A. Szasz et aL / The metastable states of some amorphous Fe-B alloys

/

acf. en. {k J/tool) 550

Table 2 Measured parameters and the calculated e / a

~50.

e/a

Tcryst (°C)

AQ (J/mg)

Fesl.sTisB13.5 Fesl.sCrsB13.5 Fe83.sMo3B13.5 Fes3.5Ta3B13.5 Fe85.sAUlBa3.5 Fe83.sAu3B13.5

7.125 7.225 7.265 7.235 7.355 7.415

560 467 522 546 565 481.5

59.5 231.5 103.9 78.5 142.3 241.0

is the energy difference between these states, introduces a thermodynamic driving force to destroy the metastable state and to reach the lowest possible energy for the system. In practice, the E~ is not easy to measure. We have chosen an easier way: to approximate E a by Tc~t at a fixed heating rate. Among these circumstances, Tc~yst linearly depends on E a for the Fe-B-based ternary TM alloys [20]. We have verified this assumption by comparing available data on E, from literature with our values of Tcryst for the FeBW ternary system (fig. 6) [37]. Based on this assumption, we have measured T~ryst to determine AQs and the actual driving force for the system to escape from this local minimum. The measured values show a monotonic, almost linear dependence of Tc~ys, and AQ on e/a

350

250

Sample

two

Fig. 6. Dependence of the activation energy with Tc,vs,. The dashed line is only a guide for the eye. The labels of the points correspond to the TM alloying element.

the D T A data. The activation energy, Ea, of the crystallization is dependent on the energy barrier which prevents the metastable state from decaying to a stable state with lower energy [33]. On the other hand, the crystallization heat, AQ, which

6000C

"~-.. 5500C

[3

os >,

5000C

4500C

4000C00

710

2'20

7' 3 0

740

7.0

@/o

Fig. 7. The dependence of Tcryst and e / a . The dashed line is only a guide for the eye. The labels of the points correspond to the TM alloying element.

54

A. Szasz et al. / The metastable states o f some amorphous F e - B alloys

between E F and the median energy of DOS, being - 2 . 0 1 eV and - 2 . 9 2 eV for a-FessB15 and a-Fe75B25, respectively [22]; ('a' denotes the amorphous state). Consequently, the covalent bond conception [41] needs some refinement, because of the differences between the stabilities of alloys containing a small fraction of various TMs. More confusing is the fact that, for a slight increase of concentration of the TM, the stability increases. The effects of the stabilization of the electronic structure are discussed in terms of structural concept [40]. The electronic stabilization is observed in the case of different metastable phases [39,40,41]. We suggest for the ternary Fe86.5_x-TMxB13.5 systems the same effect: the stabilization of the metastable states is due to the electronic structure. Now, how can were solve the contradiction between the inapplicability [21] of the nearly free-electron models and the observed electronically governed stability? In these (Fe-TM)s6.sB13.5 alloys the TM concentration, relative to Fe, is small (about 3.5% on average). Assuming a homogeneous spatial distribution of TM atoms in the phase, every 28th atom is T M in the system. The first coordination sphere of Fe consists of 12-16 atoms [42] in amorphous F e - B systems; therefore, at this TM

(table 2, fig. 7 and fig. 8), but their slopes are opposite to each other. Similar results were obtained by others also, on the a set of samples [20] with higher boron content. (Our smaller boron content was chosen to be far from the polymorphic reactions, and so the ~-Fe precipitation occurs independently of the crystallization process

[38].) The thermodynamic data (DTA) are in agreement with the electronic data (SXFS spectra) where the stability is monitored [32] by the centered position (average band-energy, Ear) which is calculated [39,40]:

Eav=(foE~En(E) dE)( f?Vn(g) dE) -1, where n(E) is the density of states (DOS) function. The formula above provides directly an average electronic energy. The variation of Eav as a function of and as a function of other electronic and thermodynamic parameters (fig. 9) are correlated, which is a direct and strong support of the electronic stability criteria. In our case, the average band energy can be replaced by the HBW, because E F is fixed to the vacuum level. The change of H B W versus is given in fig. 10. This dependence is in good agreement with the calculation of the difference

e/a

e/a

e/a

/

2'~000,

/ / / /

2000C

/ / / /

"•

/

15000

/ / /

v ©

/ /

1000C

/ /

u

/

u/ /

50.0C

/

/ / / 00C070 .

i. 1 1 1.

. . 710

i 720

. . . .

i . . . . 730

4/ . . . . 7 0

I 750

e/a

Fig. 8. The dependence of AQ and

e/a. The dashed line is only a guide for the eye. The labels of the points correspond to the TM alloying element.

A. Szasz et al. / The metastable states of some amorphous Fe-B alloys

concentration each second coordination sphere of Fe contains a TM atom. In these ternary alloys, in which TM has higher affinity to boron than does Fe [41], in the first step pure o~-Fe precipitation is expected. Consequently we assume that the transition metal atoms are in the non-precipitated part of the alloy. This assumption is supported by the constant precipitation temperature (fig. 4). In this approximation, only the excess Fe precipitates before the primary crystallization. The second coordination sphere of Fe 184,

55

does not have a large influence on the a-Fe precipitation process in the first stage. The driving force, which pushes away the Fe from the homogeneous alloy, mainly has a chemical origin [35]. The precipitation fixes the chemically stable [43] amorphous Fe3B-type phase by localizing excess Fe, similarly to the processes the supersaturated solid solutions (give citations). The ineffective TM in the second coordination sphere of Fe in the precipitation process is consistent with the hypothesis of localized, short-range chemical

(b)

184

(a)

~J o3

Mo3

Mo3

c

Au3 ~ ~" 183

183

Aul

Cr~/

Au3

ol o

f

o t_

ref.

•

r

L

1

Cr5

Ta3

"~

f

Ti5

3~ 18~ -ZlO

715

720

Z25

Z30

Z35

7.40

745

182 6.0

6.5

Z0

7..5

e/o

184

(C)

184

Mo3 183 o~ o

L <~

Aul

Ta3. I "i5t •

182 50

100

8.0

8.5

9.0

HBW (eV)

~

I

~

I

L ~ c e ~

-~'

clQ ( J / • g )

200

Mo3

" -~ Au3 183 "~n.~

Aul •

~

o

Cr5 •

150

(d)

~ ~

250

:r5

~

•

182 460

480

500

Ta3 ~ "4' . . T i 5

520

T<~y~t

540

560

580

(°C)

Fig. 9. The average band-energy, Ear , versus some electronic and thermodynamic parameters. The dashed line is only a guide for the eye. The labels of the points correspond to the TM alloying element. (a) Ear versus e / a ; (b) Ear v e r s u s H B W ; (c) Ear versus d Q ; (d) Ear versus Tcryst.

56

A. Szasz et al. / The metastable states of some amorphous Fe-B alloys

HBW (eV) £0

\ \

-T+ Ii

\.. \ \\ \- \

Cr~.

".~Mo~ "-, Au,.. \

7.~

z2

z3

(e/a)

Fig. 10. The half-bandwidth of SXFS spectra versus e / a . The dashed line is only a guide for the eye. The labels of the points correspond to the TM alloyingelement.

driving forces expected for the mainly covalenttype bonds [21,22]. On the other hand, the transition metal alloying affects the primary crystallization, i.e., the amorphous-to-crystalline phase transition. In these transitions, after the precipitation of the e~-Fe, the remaining elements have, in every case, 'Fe3B'-type composition. The relative TM concentration increases by the Fe precipitation, and becomes about 8%. The coordination number in the first sphere for Fe is about the typical closepacked value, 12 [28]. Assuming the homogeneous distribution of TM atoms in the (FeTM)3B amorphous phase (normal solid solution), we conclude that every first coordination sphere of Fe contains one of the T M atoms. The T M - F e interaction is essential in this new phase and is not negligible. This interaction is also in accordance with the covalent-bond model [22], where the B 2s state hybridizes with transition metal (Fe and TM) s and p states, as well as a bonding state created between B 2p and TM d-states. Due to this precipitation process, however, the chemically required stochiometric composition is created ('Fe3B'). Every composition of the dilute ternary F e - B - T M alloys has the (FeTM)3B composition before crystallization. (The concentration of B has to be less than 18% [38] to avoid the polymorphic process.) The value of E v for Fe3B just corresponds to

a minimum of the DOS [44], in agreement with the behavior predicted by the N a g e l - T a u c theory. The same effects are expected for the (FeTM)3B alloys when the TM concentration is smaller. Consequently, after the precipitation of the excess Fe from the alloy, the material is in chemical equilibrium. The 'Fe3B'-type ((Fe, TM)3B) stochiometric form is locally stabilized [45] by the electronic band structure. The bandstructure stabilization contains the hybridization effects which reduces the total electronic energy of the amorphous state [21], this stabilizing the structure. The hybridization of B 2p and 3d states can become important. In low TM content amorphous Fe-B-based ternary alloys, having TM atoms in every first coordination sphere of Fe, the stability will decrease by an increase of the d state band splitting. In the case of higher TM concentrations, the electronic structure stability decreases [46]. Note that the relatively large effect of TM atoms is in agreement with the assumption that in the amorphous F e - B system the chemical bonds are stronger among Fe (or TM) atoms than in their crystalline counterpart [47]. We note some similarities between our ideas and the recent stability theory of Buschow [48] and Lasocka et al. [49]. It was shown that the stability of amorphous binary alloys can be described in terms of a simple kinetic model, where the activation energy for crystallization is taken to be proportional to the formation enthalpy of a structural hole, A H (the size of the smaller type of atoms) [50], or it depends linearly on the average atom enthalpy, A H a [49]. Generally, it can be shown [32] that the vacancy formation energy, Ev, and the sublimation enthalpy are proportional to each other, and the hole formation enthalpy can be expressed by the monovacancy formation enthalpy of the binary system. In the same way, the vacancy formation energy is proportional to the average specific lattice energy of one atom [51]. The vacancy formation is strongly related to the electronic structure [52]: E F linearly depends on the E v [53]. In this way, the expected linear dependence on e / a of the stability of amorphous alloys is supported by a simple kinetic model as well.

A. Szasz et al. / The metastable states of some amorphous Fe-B alloys

5. Conclusion In o u r p r e s e n t p a p e r , e v i d e n c e f o r t h e e l e c t r o n i c stability in Fe86.5 x T M x B 1 3 . s a m o r p h o u s alloys a r e p r e s e n t e d a n d a n a p p a r e n t c o n t r a d i c tion between the observed data and the NagelT a u c s t a b i l i z a t i o n t h e o r y is e x p l a i n e d . I n g e n e r a l we expect that a large branch of the highly m e t a s t a b l e alloys a r e locally s t a b i l i z e d by t h e i r electronic structure. This local stabilization was observed on the GP zone forming aluminium alloys as w e l l [54]. T h e a u t h o r s a r e g r a t e f u l to M r J. H a j d u a n d M r J. K o l l a r for a s s i s t a n c e in D T A m e a s u r e m e n t s , a n d to P r o f e s s o r E. N a g y f o r f r u i t f u l discussions. T h i s w o r k w a s s u p p o r t e d by t h e A u s trian Ministry of Research East West Cooperation. T h e a u t h o r s a r e d e e p l y i n d e b t e d to D r A . L o v a s a n d D r G. K o n c z o s for p r o v i d i n g t h e s a m ples for the present investigations.

References [1] See, for example, G.E. Murch, ed., Phase Stability and Phase Transformations (Proc. Conf. Bombay, 1984), Mater. Sci. Forum 3 (1985). [2] L.H. Bennett, ed., Theory of Alloy Phase Formation (Metallurgical Society of the AIME, Warrendale, PA, 1980). [3] R.W. Cahn, in Physical Metallurgy, ed. R.W. Cahn and P. Haasen (North-Holland, Amsterdam, 1983) ch. 28, p. 1779. [4] W. Hume-Rothery, Electrons, Atoms, Metals and Alloys (lliffe, London, 1946). [5] W. Hume-Rothery and G.V. Raynor, The Structure of Metals and Alloys (Institute of Metals, London, 1954). [6] W.B. Pearson, The Crystal Chemistry and Physics of Metals and Alloys (Wiley-Interscience, New York, 1972). [7] W. Gordy and W.J.O. Thomas, J. Chem. Phys. 24 (1956) 439. [8] L. Pauling, The Nature of the Chemical Bond (Cornell University, Ithaca, NY, 1960). [9] W. Hume-Rothery, G.W. Mabbott and K.M. ChannelEvans, Philos. Trans. R. Soc. A233 (1934) 1. [10] F. Laves, in: Theory of Alloy Phases (American Society for Metals, Cleveland, OH, 1956) p. 124. [11] W. Hume-Rothery, J. Inst. Met. 35 (1983) 295, 307. [12] N.F. Mott and H. Jones, The Theory of the Properties of Metals and Alloys (Dover, New York, 1958).

57

[13] N. Engel, ASM Trans. Quant. 57 (1964) 619. [14] L. Brewer, in: Electronic Structure and Alloy Chemistry of the Transition Elements, ed. P. Beck (Wiley-lnterscience, New York, 1963) p. 87. [15] J.A. Alonso and N.H. March, Electrons in Metals and Alloys Academic Press, London, 1989). [16] J. Hajdu, L. Kertesz, Cs. Lenart and E. Nagy, Cryst. Latt. Def. 5 (1974) 177. [17] I.G. Brytov, E.A. Obolenskii, M.S. Goldenberg, L.G. Rabenovich and T.M. Autoeva, Prib. Tekh. Eksp. 1 (1983) 288 (in Russian). [18] Technology is presented in: I. Nagy, C. Hargitai and Cs. Kopasz, Key Eng. Mater. 13-15 (1987) 837. [19] Samples were made in the Central Institute of Physics of Hungarian Academy of Sciences by Dr G. Konczos and Dr A. Lovas. [20] These alloys were made in the Central Institute of Physics Budapest, and various measurements and publications were done on these materials: A. Lovas, L. Granasy, K. Zambo-Balla and J. Kiraly, in: Proc. Conf. on Metallic Glasses: Science and Technology, Budapest, 1980, Vol. 2, p. 291: L. Granasy, A. Lovas, I. Kiss, T. Kemeny and E. KisdiKoszo, J. Magn. Magn. Mater. 26 (1982) 109; New X-ray check of the samples were done just before the measurements. [21] M. Tanaka, M. Yashino and K. Suzuki, J. Phys. Soc. Jpn. 51 (1982) 3882. [22] T. Fujiwara, J. Phys. FI2 (1982) 661. [23] G. Wiech, in: Soft X-ray Band Spectra, ed. D.J. Fabian (Academic Press, London, 1968) p. 59. [24] T. Kemeny, I. Vincze, B. Fogarassy and S. Araj, Phys. Rev. B20 (1979) 476. [25] A. Lovas, L. Potocky, A. Czir~iki, E. Kisdi-Koszo, t~. Zsoldos, L. Pogfiny and L. Novfik, Z. Phys. Chem. NF 156 (1988) 425. [26] T. Kem6ny, thesis for Cand. Sci., Hungarian Academy of Sciences (1986). [27] Y. Waseda and H.G. Chen, Phys. Status Solidi (a)49 (1978) 387. [28] T. Fujiwara, H.S. Chen and Y. Waseda, J. Phys. F l l (1981) 1327. [29] A. Szasz, J. Non-Cryst. Solids 127 (1991) 121. [30] D.G. Pettifor, in: Physical Metallurgy, eds. R.W. Cahn and P. Haasen, Vol. 73 (North-Holland, Amsterdam, 1983) ch, 3. [31] R.W. Cahn and P. Haasen, eds., Physical Metallurgy (North-Holland, Amsterdam, 1983): T.B. Massalsky, ch. 4, p. 153; K. Giris, ch. 5, p. 219. [32] A. Szasz and D.J. Fabian, Solid State Commun. 65 (1985) 1085. [33] A. Szasz, L. Kertesz, M.A. Aysawy, H. Kirchmayr, H. M/filler and L.M. Watson, J. Non-Cryst. Solids 130 (1991) 211. [34] S.R. Nagel and J. Tauc, Phys. Rev. Lett. 35 (1975) 380.

58

A. Szasz et al. / The metastable states o f some amorphous F e - B alloys

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