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KFKI-1980-90
I . V I N C Z E T . KEMÉNY
A iSi S C H A A FS M A A . 1 O V A<5
F , V A N DER WOUDE
CHEMICAL AND TOPOLOGICAL SHORT-RANGE ORDER IN METALLIC GLASSES
' Hungarian 'Academy of'Sciences CENTRAL
RESEARCH
INSTITUTE FOR PHYSICS
BUDAPEST
KFKI-1980-90
CHEMICAL AND TOPOLOGICAL SHORT-RANGE ORDER IN METALLIC GLASSES
I. Vincze*+ , T. Kemény, A.S. Schaafsma*, A. Lovas, F. van der Woude*
Central Research Institute for Physics H-1525 Budapest 114, P.O.B. 49, Hungary
♦Solid State Physics Laboratory, University of Groningen, The Netherlands
To appear in the Proceedings of the Conference on Metallic Claeses:
Science and Technology, Budapest, Hungary, June 30 - July 4, 1980;
Paper S-19
HU ISSN 0368 5330 ISBN 963 371 736 1
On leave from the Central Research Institute for Physics, Budapest
АННОТАЦИЯ
Ближний порядок металлических стекол /Fe,Ni/В, полученных быстрым ох
лаждением расплава, очень похож на порядок аналогичного кристаллического ма
териала /Fe^B: тетрагональный, Ni~B: орторомбический/. В области большой кон
центрации атомов N1 распределение атомов переходных металлов не случайное.
Атомы Ni чаще попадают на места, соседствующие с большим числом атомов бора.
KIVONAT
Olvadék gyorshütésével előállított (Fe,Ni)В üvegek rövidtávú rendje igen hasonló a megfelelő kristályos anyagéhoz (FegB: tetragonális, Ni^B: ortorom- bos). Az átmeneti fématomok eloszlása nem véletlenszerű a Ni-dus összetétel
tartományban; a Ni atomok nagyobb gyakorisággal kerülnek a több В szomszéd
dal rendelkező helyekre.
ABSTRACT
The atomic a r r a n g e m e n t in m e l t - q u e n c h e d (Fe,Ni)B glasses clo s e l y resembles that of the crystalline c o u nterparts (FeßB is tetragonal, N i 3B is o r t h o r h o m b i c ) . The d i s t r i b u t i o n of transition metal atoms
is not r a n d o m at h i g h Ni concentrations: Ni atoms prefer a n e i g h bourhood wit h a h i g h e r boron coordination.
In the study of chemical shor t - r a n g e order M ö s s b a u e r s p e c troscopy is very u s e f u l because of its s e n sitivity to nearest- neighbour environments. Two types of infor m a t i o n can be obtained
from M ö s s b a u e r experiments: 1. the iron hyperfine field is p r o portional to the iro n magnetic m o m e n t in t r a n sition m e t a l - m e t a l
loid glasses and it is d e t ermined [1] m a i n l y by the number of nearest m e t a l l o i d neighbours. Thus the hyperfine field d i s t r i b u tion gives the d i s t r i b u t i o n of the local m e t a l l o i d c o o r d i n a t i o n number a r ound iron atoms. 2. the g e o m e t r i c a l arran g e m e n t of m e t a l loid neighbours is reflected in the qua d r u p o l e interaction.
It has been s h o w n [2] that in the m e l t - q u e n c h e d s t o i c h i o metric (Fe,Ni)^B glasses both the iron hyperfine field and q u a d rupole splitting closely follow those of the c r y stalline c o u n terparts i n d i cating that the local s y m m e t r y in the amorphous and crystalline s t r u cture is similar and chan g i n g w i t h Ni s u b s t i t u tion. The m e t a s t a b l e tetragonal Fe^B c o m p o u n d formed during crystallization is [3] isostructural to Fe^P and has three cry- stallographically inequivalent iron sites in equal numbers wit h 2B, 3B and 4B n e a r e s t neighbours. For the substitution of Ni the
2
tet r a g o n a l structure transforms [4] into the- orthor h o m b i c s t ruc
ture of Ni^B (Co^B). This cementite type of crystal contains two c r y s t a l l o g r a p h i c a l l y i n equivalent Ni sites w i t h 2B and 3B nearest n e i ghbours in a 1:2 ratio. The differences in the e n vironments are clearly r e f l ected in the M ö s s b a u e r s pectra of Fig. 1. The dif f e r e n c e in the a t omic a r rangements of the tetragonal and o r t h o r hombic unit cells is also r e f l e c t e d in the densities.
- 6 - 4 - 2 0 2 4 6
velocity (m m /s ) - - - -
Fig. 1. Mössbauer spectra of crystalline Fe$B (tetragonal) and (Fe„ 77N i n _„) ,5 (orthorhombic) at 5 K. The
U • о о U • О r ó
continuous line is the fitted curve
3
T h e orthorhombic structure is m o r e densely packed: on l y half of the observed 10% increase in the density of Ni^ B comp a r e d to Fe^B can be explained by the atomic w e i g h t differences. Fig. 2 shows that the density of (Fe,Ni)8qB 2q glasses [5] follows this trend.
Sfg/cnr) 8.3
8.1
a Fe Т В
80-x x
20о Со
о Ni
7.9
7.7
7.5iíFe,B
0;\
< V"
7.3
20 40 60
$NLB3
*SCo В
X
80
Fig. 2. Densities of amorphous Feeo-x^x^20 ^ ~ ^° arLl^
alloys taken from Ref. 5. The dashed lines correspond to simple atomié weight differences assuming the packing of Fe^^B^^ or ^ q o^ 203 resV>eo^ ^ e l y . The densities of crystalline Fe.B, C o 7B and N i 7B are
- 7 7 Ó Ó О
also shown.
Ano t h e r ma n i f e s t a t i o n of the change in the local e n v i r o n ments of (Fe,Ni)В glasses is the В c o ncentration dep e n d e n c e of
the Curie temperatures {Fig. 3). The T c cannot be m e a s u r e d in the
Fig. 3. Curie temperatures of amorphous
{Fe Ni ) г, г, В 0r 1-x x 7 5+y 25-y alloys measured by Mössbauer and DSC methods
У = 5* l
(y = °>
= 1 0).
4
whole concentration range because c r y s t allization occurs at lower temperatures. However, it is clear from Fig. 3 that decreases on the Fe-rich side w i t h decreasing В co n c e n t r a t i o n while the opposite is valid for the Ni-rich side. These opposite trends i n dicate the different electron structure of these glasses due to the different atomic structure.
The change in the topological arra n g e m e n t at the Fe by Ni substitution can be seen easily in the fine structure of the Mössbauer spectra {Fig. 4 ). The second line is always narrower
_____ i______ I______ I______I______I______ I______ I_______
-6 - U -2 0 . 2 U 6
velocity (mm/s) ---
Fig. 4. Typical Mössbauer spectra of amorphous {Fe3N i )q qB^q measured at 5 К
5
than the fifth line (numbering is from left to right)'but in the case of F e 0_B„_ the width of the lines 1 and 6 is about equal
oü ZU
(Г, ~ Г ,) while Г., > Г, was found on the Ni-rich side. The former is a result of the c o m p e n s a t i o n of the co r r e l a t e d isomer shift and quadrupole shift d i stribution (all of them - including the hyperfine field - are d e t ermined by the diffe r e n t metal l o i d c o n figurations) . In the case of Ni based gla s s e s the q u a d rupole i n teraction is about 50% stronger [2] due to the different local surroundings which o v e r c o mpensates the e f f e c t of isomer shift and results in and Г’2 < Г,- (the qua d r u p o l e interactions i n fluence the lines 1,6 and 2,5 in opposite ways). It is w o r t h w h i l e to emphasize that this type of asymmetry is c haracteristic for environments o c c u r i n g in the orthor h o m b i c structure as it can be seen from the M ö s s b a u e r spec t r u m of the crystalline m a t e r i a l shown in Fig. lb.
The d i s tribution of iron atoms in d i f f e r e n t local e n v i r o n ments is given by the hyperfine field distribution, p(H). The narrowing of this d i s t r i b u t i o n corresponds to a sharper, mo r e
"ordered" distri b u t i o n of iron atoms. Fig. 5 and 6 show that in the B 2q and B^,- o f f - s t o i c h i o m e t r i c gl a s s e s the d i s t r i b u t i o n of Fe environments is n a r r o w e r for higher Ni concentrations. In the
Fig. 5. Typical iron hyperfine field distributions of amorphous (Fe3Ni) measured at S К
6
case of (Fe,Ni)^B glasses the standard deviation of the iron hyperfine field distribution, is constant. (This appar e n t con
centration independence is due to compen s a t i n g c o n c e n t r a t i o n d e pendences [4] of the iron hyperfine field with d i f f erent number of В neighbours as the constancy of for the d i f f erent crystal structures s h o w s ) . As a result of this comparison we had to con
clude that the narrowing of p(H) is c aused by the increasing
number of iron atoms mostly on o f f - s t o i c h i o m e t r i c c r y s t allographic sites, w h i c h are not present in (Fe,Ni)^B. This is the first d i rect evidence that the distribution of transition m e tal atoms is not random at high Ni concentrations in (Fe,Ni)B glasses: the Fe atoms prefer less В neighbours than the Ni atoms. The pres e n c e of stronger N i -В than Fe-B interaction is also suggested by recent simple cluster calculation of M e s s m e r [6].
Fig. 6. Standard deviation of the iron hyperfine distributions in amorphous (Fe1 Ni )7 r, B 0l._ measured at 5 K. Empty
1 CC CC ( О I у а и у
circles stand for crystalline {Fe3Ni)^B compounds.
We are grateful to Prof. A.J. D ekker for s t i m u l a t i n g d i s cussions. This wor k forms part of the research p r o g r a m of the Foundation for Fundamental Research on M atter (FOM), w i t h finan
cial support from the Netherlands O r g a n i z a t i o n for the A d v a n c e ment of Pure Rese a r c h (ZWO).
7
REFERENCES
[1] I. Vincze, F. van der W o ude and J. Balogh, J. de Physique £1 (1980) Cl-257.
[2] I. Vincze, F. van der Woude, T. Kemény and A.S. Schaafsma, J. Magn. Magn Mat. 15-18 (1980) 1336; A.S. Schaafsma, I.
Vincze, F. van der Woude, T. Kemény and A. Lovas, Interna
tional Conference of L iquid and A m o r phous Metals, Grenoble 1980, to be p u b l i s h e d in J. de Physique.
[3] U. Herold and U. Köster, Z. Metallk. 6_9 (1978) 326; W.B.
Pearson, Handbook of Lattice Spacings and Structure of Metals V o l . 2, Pergamon Press, O xford (1967).
[4] T. Kemény, I. Vincze, J. Balogh, L. Gránásy, В. Fogarassy, F. Hajdú and E. Sváb, this conference (T-14).
[5] R.C. O'Handley, R. Hasegawa, R. Ray and C.P. Chou, Appl. Phys Letters 29^ (1976) 330.
[6] R.P. Messmer, submitted to Phys. Rev. B; this conference (S-ll).
Kiadja a Központi Fizikái Kutató Intézet Felelős kiadó: Tompa Kálmán
Szakmai lektor: Hargitai Csaba Nyelvi lektor: Hargitai Csaba Gépelte: Végvári Istvánné
Példányszám: 220 Törzsszám: 80-630 Készült a KFKI sokszorosító üzemében Felelős vezető: Nagy Károly
Budapest, 1980. október hó
