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MÖSSBAUER EFFECT STUDY OF STRUCTURE OF AMORPHOUS ALLOYS
F. Fujita
To cite this version:
F. Fujita. MÖSSBAUER EFFECT STUDY OF STRUCTURE OF AMORPHOUS ALLOYS. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-120-C2-122. �10.1051/jphyscol:1979241�. �jpa-00218639�
JOURNAL DE PHYSIQUE Colloque C2, supplkment au n o 3, Tome 40, mars 1979, page C2-120
M~sSBAUER EFFECT STUDY OF STRUCTURE OF AMORPHOUS ALLOYS
F. E. Fujita.
Faculty o f Engineering Science, Osaka University, Toyonaka, Osaka, Japan.
R6sumd.- La structure atomique et dlectronique d'alliages amorphes ferromagndtiques Fe-P-C, Fe-B et Fe-Si ont dtd dtudids par spectroscopic ~Zssbauer. En tenant compte de l'existence d'un ordre 3 courte distance dans les structures amorphes, les spectres obtenus ont dtd analyses en supposant que les configurations proches voisines sont pratiquement les mgmes que dans l'dtat cristallin. La distribution de champ interne, le ddplacement isomdrique et l'effet quadrupolaire ont dtd interprd- tds de la m2me manisre.
Abstract.- Electronic and atomic structures of Fe-P-C, Fe-B and Fe-Si ferromagnetic amorphous alloys were studied by means of MZjssbauer spectroscopy. Taking account of considerably developed short range atomic ordering in the amorphous structure, the obtained spectra were analyzed with the assump- tion that the near neighbour configurations are almost the same as those in the crystalline state.
The internal field distribution, isomer shift and quadrupole effect were interpreted along the same line.
1.Introduction.- The most popular and widely accep- ted concept in the past on the atomic arrangements in the amorphous structure of metals was the dense random packing model first proposed by Bernal / I / . In figure 1 is shown an example of histogram of the distribution of coordination numbers in the model.
Coordination number
Fig. 1 : A histogram of distribution of the coordi- nation numbers in a random dense packing model by Bernal. For comparison, the binomial distribution of foreign atoms in a 18% solid solution alloy is shown by small circles.
The random lattice structure of the amorphous alloys has been concluded from various physical properties and the halo X-ray diffraction pattern, which are respectively comparable to those of li-
quid metals. However, the amorphous alloys have a degree of order higher than that of molten metals.
For instance, the diffraction pattern of the former is torelably sharp; especially its second maximum shows a clear split, and its two body corelation function also exhibits the second maximum split.
The dense random packing models have suffered va- rious examinations and improvements primarily so as to fit the X-ray diffraction studies 12-6).
Nevertheless, there exist some more impli- cations for much higher degree of ordering in the amorphous state than what would be expected from usual dense random packing models. For instance,
Doi / 7 / concluded from a new X-ray analysis that
the atoms may have good ordering along about five atomic distances, and Ninomiya 181 showed that a crystal structure containing a large number of dis- locations could represent the amorphous structure.
Many physical properties and characteristics of the amorphous alloys also reflect the crystalline na- ture 191.
Since the crystalline field in a solid is perturbed by the neighbouring configurations, the MEssbauer spectroscopy looks useful to elucidate the electronic and defect structure in the amor- phous alloys.
2. Result and discussion. - FesoPl sC7, FeeoPljlCs /10,11) and Fe78-88B22-1z./12/ alloys were made amorphous by rapid cooling from the melt and exa- mined by usual transmission method using 30mCi
5 7
Co source. Amorphous thin films of FesoSiso and Fe30SiTo alloys 1131 were made by vacuum evapora-
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979241
tion and examined by the-conversion electron re- flection method. Exept the last one, all amorphous alloys exhibited broad six line spectra at room temperature, as the upper two figures in figure 2 show. The second and fifth peaks were always large, showing the magnetic polarization nearly in the film direction, which could not be dismissed in the spectral analyses.
In the Fourier analysis, no special neighbou- ring configurations were assumed but only the distri- bution of six line Lorentzians with various spreads was seeked for. Good agreements between the analy-
tical curves and the experimental data are seen in figure 2.
a) Fesoq,C3. Amorphous
, ,
Doppler Velocity (mmls)
Fig. 2 : Miissbauer spectra of amorphous FesoPl.~C~, amorphous FessB17, and polycrystalline Fe7oV3oso- lution alloy.
Examples of the distribution analysis for amorphous Fes3B17 and FesoSiso alloys are shown by the full lines, A and B, in figure 3. The dotted line, C, was obtained by Tsuei et al. 1141 from an Fe-P-C
amorphous alloy. Their result looks interesting since the distribution spreads even to zero field.
However, their result is not justified, because the above mentioned polarization effect was not taken into account.
When the resolution of the spectroscopy was improved fine structures appeared as small shoul- ders and kinks in the spectra, which did not cor-
respond to any chemical compounds conceivable among the constituent elements. This strongly suggested various distinct near neighbour configurations in the amorphous alloys and lead us to the further step to analyze the structure of amorphous alloys.
For the above purpose, another method of analysis was employed with some basic assumptions.
In the first, one has to assume either a defective structure like dense random packing models and/or local disturbances in the alloy structure.
Fig.3 : The internal field distribution curves for Fes3B17 amorphous alloy (A), FesoSiso a~norphous alloy ( B ) , obtained by the Fourier analysis, and FegOPI7C3 amorphous alloy (D) reconstructed from the near neighbour configuration analysis. Curve C is for Fe75P15Clo amorphous alloy by Tsuei et al.
By utilizing the distribution of the coordination deficiencies in figure 1 and assuming the linear reduction of the internal field with the coordina- tion deficit number, Gonser et al. / I / analyzed a Mksbauer pattern of amorphous Fe-B alloy, and concluded that one deficiency reduced the internal field by about 30 kOe. However, an essential dif- ficulty wlth this kind of calculation is that the actual materials are solution alloys in which the foreign atoms have a coordination distribution like that in figure 1 , as shown by small circles, and the local disturbances of the same order of magnitude as the above. It is worthy of note in this respect that the three patterns in figure 2 look very similar even though the lowest one is of a crystalline solution alloy. This means that the appearance of such broad patterns is not al- ways characteristic of the amorphous structure but largely arises from the alloying effect.
Based upon the above fact and in accordance with the well developed atomic short range ordering mentioned before, the near neighbour configurations
for the probe atoms were assumed to be almost the same as those in the normal BCC structure and the
c2-122 JOURNAL DE PHYSIQUE
spectra were analyzed. Other necessary assumptions References were made on the half width of the basic Lorent-
zians, the linear changes of the internal field and isomer shift, and a simple binomial distribu- tion of mettalloid atoms at the substitutional po- sitions. Distinction between the substitutional and interstitial positions in amorphous alloys has been discussed elsewhere 1121.
Very good agreements between the calculations and experimental data have been obtained. In figu- re 3, the internal field distribution in an Fe-P-C amorphous alloy reconstructed from the above ana- lysis is shown by curve D. The calculated amount of reduction of internal field by one neighbour fo- reign atom was of the same order of magnitude as those in the crystalline state. The isomer shift distribution was rather narrow compared with those in the crystalline state, and this seems to be a characteristic of the amorphous alloys. Combination of the alloying effect and defect effect in the analysis would be possible when the latter is cla- rified more by further investigations.
The author wishes to express his hearty thanks to Drs. R. Oshima, K. Yamakawa and T. Sohmura for their cooperations and discussions.
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