Current Topics in Amorphous Materials. Physics & Technology

426 Pages·1993·16.855 MB·English

by  Y. Sakurai, Y. Hamakawa, K. Shirae, T. Masumoto and K. Suzuki (Eds.)

CURRENT TOPICS IN
AMORPHOUS MATERIALS
PHYSICS & TECHNOLOGY
Edited by
Yoshihumi Sakurai
Yoshihiro Hamakawa
Tsuyoshi Masumoto
Kimisuke Shirae
Kenji Suzuki
1993
NORTH-HOLLAND
AMSTERDAM · LONDON · NEW YORK · TOKYO
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Library of Congress Cataloging-in-Publication Data
Current topics in amorphous materials : physics and technology /
edited by Yoshihumi Sakurai ... [et al.],
p. cm.
Includes bibliographical references and index.
ISBN 0-444-81576-7 (acid-free paper)
1. Amorphous substances. 2. Solids. 3. Magnetic materials.
4. Order-disorder models. I. Sakurai, Yoshihumi.
QC176.8.A44C87 1993
530.4' 13-dc20 93-2107
ISBN: 0 444 81576 7
© 1993 Elsevier Science Publishers B.V. All rights reserved.
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Preface
In the recent decade, remarkable progress has a recent decade. To keep some continuity of
been seen in the field of disordered materials R&D activities in this new field, a research com-
in both science and technological aspects. One mittee (the so-called No. 147 committee) has
big reason to promote this progress is the great been organized by Japan Society of Promotion
advances made in material preparation technolo- of Science (J.S.P.S.) with members of 34 university
gies. These advances are supported by ultra high groups including government institutes and also
vacuum techniques, ultra purification of inorganic 29 groups from related industries in Japan.
elements and precisely synthesized heat treatment This review addressing the current state of the
technologies which includes the rapid quenching art in the physics of amorphous materials and
of thin film materials. Another reason for the its practical applications are edited as one of the
progress might be development of a series of new summary report of recent activities of the 147 Re-
material characterization methods and their com- search Committee Meeting in JSPS. Because of
puterized measurement systems. As a result, in- the keen interest in these new technological in-
dustrialization of amorphous material has been novations in the amorphous material application
initiated in the field of amorphous metals, amor- fields, particular emphasis has been place on some
phous magnetic materials and amorphous semi- important basic knowledges and current topics in
conductors. the application fields which include informations
In the fiscal year from 1980 to 1982, a spe- directly useful to scientists and R&D engineers
cial research project on the physics and technology of in industry institutes and university laboratories.
amorphous matenals was organized by the Min- Since this review is the first volume, the editors
istry of Education. It has a budget of ¥690 million have compiled an integrated information list start-
(about US$3 million) for a three year period. ing from recent 5 years in the field. It is all editor's
This project involves four parts: (1) the physics earnest hope that this new edition will contribute
of disordered material, (2) amorphous metal tech- to promote this newly born solid state science and
nology, (3) amorphous magnetic materials, and rapidly expanding application field.
(4) amorphous semiconductor technology. With
Editor in Chief,
aid of this accelerative promotion by the Special
Yoshifumi Sakurai
Research Project, a remarkable progress has been
made in not only basic physics but also technical Minoo, Osaka, Japan
developments in the application fields within just Mid Summer 1992
Current Topics in Amorphous Materials: Physics and Technology
edited by Y. Sakurai, Y. Hamakawa, Τ Masumoto, K. Shirae, K. Suzuki
© 1993 Elsevier Science Publishers B.V All rights reserved.
Introduction
Kenji Suzuki
Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980, Japan
Amorphous materials have still attracted strong Committee organized under the Japan Society for
attention because of two reasons. One comes from the Promotion of Science.
the fundamental aspect that the amorphous ma- This part is divided into the following sections:
terial provides a promising approach to mate- - Short-range structure: reviews the high-resolu-
rials physics and chemistry as opposed to the tion studies of the short-range structure observed
perfect crystalline material. The other reason is by pulsed neutron diffraction and anomalous X-
the utilization of amorphous solids as engineer- ray diffraction using the radiation sources in-
ing materials in various advanced applications. stalled in the National Laboratory for High En-
The properties of amorphous materials are par- ergy Physics (KEK), Tsukuba.
ticularly structure sensitive, since the amorphous - Dynamical structure: reports the recent results
material stays in the non-equilibrium state having of the dynamic structure characterized by neutron
a great degree of freedom in atomic motion and inelastic scattering and computer simulation.
configuration. - Medium-range structure: discusses the medium-
Based on the current progress in the experi- range structure as obtained from direct obser-
mental characterization of amorphous materials vation using high resolution electron microscope
by using new generation radiation sources such and from spectroscopic measurement using Ra-
as pulsed neutrons and synchrotron radiations, we man scattering.
have been obtaining a better understanding about - Quasicrystals: describes the topological disorder
the atomic-scale structure and electronic proper- in the medium-range structure and the various
ties of amorphous materials. Part 1 of this book is physical properties of quasicrystals.
mainly allocated to collect the achievements made - Electronic and magnetic properties: concisely pre-
by the members of group I "Materials Physics sents current reviews on the electronic and mag-
and Chemistry" in the Amorphous Materials 147 netic properties.
Current Topics in Amorphous Materials: Physics and Technology
edited by Y. Sakurai, Y. Hamakawa, T. Masumoto, K. Shirae, K. Suzuki
© 1993 Elsevier Science Publishers B.V. All rights reserved.
Static structure of amorphous solids and liquids by pulsed
neutron diffraction
M. Misawa* and T. Fukunaga**
* National Laboratory for High Energy Physics, Tsukuba 305, Japan
**Department of Crystalline Materials Science, Nagoya University, Nagoya 464, Japan
1. Introduction length and of an isotope element with different
coherent scattering length have provided much in-
A knowledge of the static structure is essen- formation on the atomic structure of disordered
tial in understanding the physical and chemical materials. Many studies on liquids and amorphous
properties of liquids and amorphous solids. Ac- solids have been made by means of this technique
curate determination of the structure of disor- by using S(Q) instruments installed at pulsed neu-
dered materials by means of diffraction methods tron sources operated by, for example, the 500
is, however, not easy compared with that of crys- MeV proton synchrotron at KEK (National Lab-
talline materials. An essential difficulty is that oratory for High Energy Physics) or the 300 MeV
the structure factor or interference function S(Q) electron linac at Tohoku University. The follow-
obtained by diffraction experiments is only one- ing subjects have been extensively studied so far:
dimensional information on a three-dimensional (i) geometrical short-range order and chemical
atomic structure. It is, therefore, principally hard short-range order in metallic glasses; (ii) atomic-
to reconstruct the three-dimensional atomic struc- scale observation of the amorphization process
ture from the experimental S(Q)'s even in one- during mechanical alloying; (iii) the short-range
component systems. Furthermore, most practical structure of network-forming glasses; (iv) orien-
amorphous solids comprise at least two different tational correlation and packing of molecules in
chemical species. The more the chemical con- molecular liquids; and so on. Brief reviews on
stituent in the specimen increases, the more the some of them are given below.
determination of its static structure becomes dif-
ficult. For instance, one needs n(n + l)/2 par-
tial structure factors in order to describe fully 2. Geometrical short-range order and chemical
the atomic structures of an η-component system. short-range order in metallic glass
Therefore, many efforts to develop new experi-
mental techniques and new data-analyzing meth- 2.1. Metallic glass prepared by liquid quenching
ods are continuously being made in this field.
The pulsed neutron diffraction technique is one Pd-Si metallic glass is one of the typical
of such newly developed methods. It has the metal-metalloid systems easily prepared by rapid
advantage, compared to other diffraction tech--1 quenching from the molten state and is a good
niques, of measuring S(Q) up to Q = 40 Â example for observing the short-range structure
or more. This advantage enables one to define by neutron diffraction, because the coherent scat-
precise short-range structures in real space with a tering length of the Si atom has an adequate mag-
high resolution even in multi-component systems nitude in comparison with that of the Pd atom.
[1]. Moreover, the use of an atom with negative Figure 1 shows structure factors S(Q) analyzed
or negligibly small coherent neutron scattering by Faber-Ziman definition [2] for Pdioo-xSix
M. Misawa and T. Fukunaga / Static structure of amorphous solids and liquids by pulsed neutron diffraction 5
Fig. 1. Faber-Ziman type structures factors S(Q) of Pdioo-x
Six (X = 15, 20, 22) metallic glasses prepared by liquid
quenching.
Fig. 2. Radial distribution functions RDF(r) derived as the
Fournier transform of S(Q) truncated various Q values for
(X = 15, 20, 22) metallic glasses [3,4]. The
PdsoSÎ2o metallic glass.
measurement of S(Q) was carried out up to
the high Q region of Q > 30Â . The radial
distribution functions RDF(r) obtained by the is between 5 to 6 atoms over the whole Β con-
Fourier transform of S(Q) for the PdsoSi2o metal- centration range. This indicates that the short-
lic glass, truncated at various Q values, are shown range structure of the Ni-B metallic glasses is
in Fig. 2 [3,4]. With the increase of the trun- also formed by the prismatic packing of 6 Ni
cated Q value, the first peak in the RDF(r) is atoms surrounding a Β atom, in good agreement
more clearly split into two subpeaks, which cor- with the short-range unit around a Β atom in the
respond to Si-Pd and Pd-Pd pair correlations. N13B and N14B3 crystalline compounds.
This assignment is confirmed by a comparison Chemical atomic arrangements of the metal-
of (RDF(r))'s between the PdsoSi2o metallic glass metal type metallic glass prepared by liquid
and PdaSi crystalline compound. The coordination quenching (LQ) have been also investigated by
numbers of the Si-Pd and Pd-Pd correlations taking advantage of neutron diffraction. Total
in the first peak of the RDF(r) of Pdioo-xSix structure factors S(Q) analyzed by Bhatia-
(X = 15, 20, 22) metallic glasses were calcu- Thornton definition [7] for the Niioo-xTi* (X =
lated and turned out to approach the values of 74, 67 and 60) neutron zero-scattering metallic
9.3 and 6 atoms, respectively, characteristic of glasses are shown in Fig. 3 [8]. The neutron zero-
the PdsSi crystalline compound with increasing Si scattering alloy can be obtained by allo yin6g 0the
content. The result supports GaskelPs [5] model nickel metal partially sub1s2tituted by the Ni1 2iso-
in which the local environment surrounding the tope (6*. = 1.03 χ ΙΟ"" , ftgj = 0.28 χ 10~ cm)
Si atom is assumed to consist of about six Pd with 12the natural titanium metal (bji = -0.33 χ
atoms forming the trigonal prism or joining two 10~~ cm), since the average coherent scattering
tetrahedra with the vertex shared by a silicon length can be adjusted mto be zero, (b) = 0. There-
atom. fore, the observed S (Q) should exhibit only
The prismatic packing was also observed for the concentration-concentration structure factor
Ni-B metallic glasses [6], the glass forming range Scc(Q)/CNCiT. i The Scc(fi) provides informa-
of which extends from 18 to 40 at% B. The co- tion on the atomic scale fluctuation of chemical
ordination number of Ni atoms around a Β atom concentration in the metallic glass.
6 M. Misawa and T. Fukunaga / Static structure of amorphous solids and liquids by pulsed neutron diffraction
Q ( A-i ) Fig. 4. Coordination numbers of Ti atoms around a Ni atom
f o in Ni-Ti metallic glasses, and NiTi2 and NiTi crystalline com-
Fig. 3. Concentration-concentration structure factors
pounds.
Scc(Ô)/CNCTii Niioo-xTi* (X = 74, 67 and 60) neutron
zero-scattering metallic glasses.
the NiTi2 and NiTi crystalline compounds agree
well with each other and is located above the solid
The radial concentration correlation function line mentioned above. This also lends support to
Gcc(r), defined as the Fournier transform of the preferential location of Ti atoms around a Ni
Scc(Q), shows a negative peak at r ^ 2.5 Â. atom in the Ni-Ti metallic glass.
This implies a preference for the Ni-Ti unlike
atom pair in the Ni-Ti metallic glass. It is also 2.2. Metallic glass prepared by mechanical alloying
found that the preferential Ni-Ti bonding at
2.54 Â coincides well with the Ni-Ti atom pair in Recently, mechanical alloying (MA) has been
the NiTi2 crystalline compound. The interatomic recognized as a novel method for synthesizing
spacing of 2.54 À is much smaller than that cal- not only equilibrium but also non-equilibrium ma-
culated from the diameters of Ni and Ti atoms terials by solid-state reaction [10]. The milling-
((σ + στ0/2 = 2.71 Â). This strongly suggest, induced amorphization gradually proceeds in the
Νί
that in the amorphous state, there exists a chem- time scale of a few tens or hundreds of hours.
ical affinity between Ni and Ti atoms in the same Therefore, the Ma technique in combination with
sense as that of the NiTi2 crystalline compound. the diffraction experiment provides a unique op-
To evaluate the preference for the Ni-Ti unlike portunity of studying the gradual transition from a
atom pair more quantitatively, the Warren chem- crystal to an amorphous structure. Figure 5 shows
ical short-range order parameters a [9] of the a series of S(Q) during the amorphization of
Ni-Ti metallic glasses were calculated, the values N140V60 powders, which proceeds with increasing
of which turned out to be -0.102, -0.141 and milling time [11]. Since the coherent neutron scat-12
-0.116 for the Niioo-xTi (X = 74, 67 and 60) tering length of the V atom (by = 0.038 χ 10~
x
metallic glasses, respectively. The negative value cm) is negligibly small com1p2ared with that of the
of a means the preferential bonding between the Ni atom (6Ni = 1.03 χ 10" cm), the S(Q) exclu-
Ni and Ti atom pair at the nearest-neighbours sively represents the Ni-Ni partial structure, the
coordination. The coordination numbers ZNÎTÎ of features of which are seen to transform gradu-
Ti atoms around a Ni atom, calculated from the ally from fee crystal to the amorphous state. The
chemical short-range order parameter, are plot- Bragg peaks of the fcc-Ni crystal before milling
ted in Fig. 4 with the corresponding ZNÎTÎ for rapidly weaken and become broadened with in-
the NiTi2 and NiTi crystals. The solid line repre- creasing milling time. After 800 hours of milling
sents ZNÎTÎ for a statistically random distribution ^NiNi(ô) shows the characteristic feature of an
of atoms with the total coordination of 12 in amorphous state. Such a prepeak has been ob-
the nearest neighbour. The coordination number served in the SNÎNKÔ) of the sputter-deposited
of Ti atoms around a Ni atom for the metallic Ni-42 at% V metallic glass [12] and the liquid-
glasses with different content of Ti atom and for quenched Νΐ4οΤΐ6ο [13] and NisoZrso [14] metallic
M. Misawa and T. Fukunaga I Static structure of amorphous solids and liquids by pulsed neutron diffraction 7
Fig. 5. Faber-Ziman type structure factors (S(Q) « 5ΝΪΝΪ(0))
of Ni4V06o powders after 0, 50, 100, 200, 400 and 800 hours
of MA.
glasses, and has been discussed in connection with
the medium-range ordering [12,15].
Figure 6 shows the atomic distribution spec-
tra of the Ni-Ni pair correlation together with Fig. 6. Radial distribution functions (RDF(r) ^ RDF N (ir)N) i
atomic positions of the fcc-Ni crystal. The second of Ni4V06o powders after 0, 50, 100, 200, 400 and 800 hours
and fifth peaks at r = 3.5 Â and r = 5.6 Â, of MA, together with atomic distribution of fcc-Ni crystal.
respectively, preferentially disappear with increas-
ing milling time. The same results have been ob- tributions of different atomic species. Figure 7
served during the amorphization of Q150V50 pow- shows Bhatia-Thornton-type structure factors of
ders [16] by milling. An fee crystal structure is Ni24Ti76 powders of a neutron zero-scattering
constructed by a combination of tetrahedral and composition during the amorphization process by
octahedral units. The second and fifth neighbour MA [17]. The S(Q) before milling can be re-
atoms around an origin atom form mainly the produced by a superposition of the diffraction
half octahedral units and the third, fourth, sixth patterns of Ni and Ti crystal powders. It changes
and seventh neighbour atoms form the tetrahe- gradually into the Scc(0 of the N124T176 neutron
dral units in the fee lattice. The atomic structure zero-scattering powders. The overall feature of
in an fee lattice, viewed as being built up from Scc(Q) after 800 h of milling becomes essentially
the tetrahedral and octahedral units, allows us to the same as that of the metallic glass obtained by
understand more easily the atomic rearrangement LQ. This is a clear demonstration that the alloy-
process during the milling-induced amorphization. ing at an atomic level is reached with increasing
We are led to conclude that the amorphization milling time.
process is the process in which the preferential The chemical short-range orders on the ba-
reconstruction of tetrahedral units occurs at the sis of the GQCO") of the NÎ24TÎ76 neutron zero-
expense of the octahedral units in an fee lattice; scattering metallic glasses prepared by two dif-
this is why an amorphous structure is dominantly ferent processes, i.e., MA and LQ, were com-
built up from the tetrahedral units. pared with each other. Figure 8 shows Gccir) of
The chemical structure of the amorphous phase NÎ24TÎ76 metallic glasses by MA and LQ, together
formed by mechanical alloying was studied from with Ti-Ti, Ni-Ti and Ni-Ni atomic distributions
the viewpoint of whether or not an atomic level of the NiTi2 crystalline compound. The first neg-
mixing due to milling brings about random dis- ative peak at r = 2.54 À in Gcc(0 of NÎ24TÎ76
8 M. Misawa and T. Fukunaga I Static structure of amorphous solids and liquids by pulsed neutron diffraction
Fig. 7. Bhatia-Thornton type structure factors S(Q) of NÎ24TÎ76 neutron zero-scattering powders after 0, 100, 200, 400 and 800
hours of MA.
order parameter a of the N124T176 metallic glasses
by MA was calculated to be -0.097. This negative
value is almost the same as a = —0.102 for the
N124T176 metallic glasses prepared by LQ, indicat-
ing that a similar chemical short-range structure
is formed in them. Therefore, the chemical short-
range order found in the N124T176 metallic glass
by MA clearly means that during the amorphiza-
tion process due to milling, Ni and Ti atoms do
not randomly mix with each other but tend to
maintain chemically preferential bonding in their
nearest neighbours.
3. Short-range structure of network-forming
glasses
Modification of the short-range structure of
Fig. 8. Reduced concentration correlation functions Gcc(r) =
4nrpc(cr) for NÎ24TÎ76 neutron zero-scattering metallic network-forming glasses due to an addition of
glasses prepared by MA and LQ, and Ti-Ti, Ni-Ti and Ni-Ni network modifiers was studied by means of pulsed
correlations in NiTi2 crystalline compound. neutron diffraction on some typical oxide glasses;
for example, Si0 -M 0 (M = Na, Li) [18] and
2 2
metallic glasses by MA is located at the same posi- Ge02-Na2Û systems [19]. High resolution radial
tion as that of N124T176 metallic glasses by LQ and, distribution function analyses on the Ge02-Na20
moreover, it coincides well with the Ni-Ti atom glass clearly revealed that one additive of Na2U
pairs in the N1T12 crystalline compound. The re- chemical units converts one GeU4 tetrahedron
sult implies that mixing down to an atomic level into one GeC>6 octahedron up to the concentra-
due to milling yields a chemical bond between Ni tion of 20 mol% Na 20 but that with a further
and Ti atoms. The Warren chemical short-range addition of Na20 the GeOe units return again to
M. Misawa and T. Fukunaga I Static structure of amorphous solids and liquids by pulsed neutron diffraction 9
the GeCU units and almost completely diminish at
33 mol% Na 0 [19].
2
One of the advantages of measuring S(QYs by
means of pulsed neutron diffraction is the width
of the covered g-range; that is, one can measure
S(Q) in a wide range of Q from a small-range
scattering region to a very high Q region simul-
taneously. One good example is the measurement
of S(Q) for CVD-S13N4 amorphous solid [20]. A
small-angle scattering intensity, as well as an oscil-
lation in S(Q), persisting up to a high Q region,
was observed simultaneously in this amorphous
solid. The analysis of 5(0 in a high Q region
clearly showed that each Si atom is tetrahedrally Fig. 9. Experimental structure factors Q(S(Q) — 1) of vitreous
coordinated by 4 Ν atoms while each Ν atom is and molten B203 measured at (a) 121, (b) 298, (c) 523, (d)
633, (e) 773, and (f) 1073 K.
coordinated by 3 Si atoms, but also however, that
there are significant deficiencies in coordination
numbers of Si-N, Si-(N)-Si, or N-(Si)-N pairs
in S13N4 networks. In addition, analysis of the
small-angle scattering suggested the existence of
voids about 10 Â with a volume fraction of about
4%, which might be introduced during the CVD
processing. The deficiencies in the coordination
numbers were reasonably interpreted as a lack of
neighbouring atoms around the atoms on the void
surface.
Another example is an observation of structural
differences between melt-quenched ordinary S1O2
glass and sputter-deposited S1O2 amorphous film
[21]. S(<2)'s measured by pulsed neutron diffrac-
r (nm )
tion on both samples had the following charac-
teristics: The first peak of the S(Q) of sputter- Fig. 10. Experimental radial distribution functions RDF(r) of
deposited S1O2 amorphous film was much smaller vitreous and molten B 203 at (a) 121, (b) 298, (c) 523, (d) 633,
(e) 773 and (f) 1073 K.
and broader than that of melt-quenched S1O2
glass; the former S(Q) had a small-angle scat-
tering intensity while the latter does not; while S(Q)'s of boron trioxide B2O3 were recently
both S(QYs were rather similar in the high Q measured in various thermodynamic states from
region. These observations led the conclusions the vitreous state at 121 Κ to the molten state
that both samples consist of almost regular S1O4 at 1073 K, through the glass-transition tempera-
tetrahedral units, but also however, that the cor- ture Jg of 540 Κ [22]. The S(ô)'s measured at
relation range in the atomic distribution of the various temperatures are compared in Fig. 9. Ra-
sputter-deposited film is about 17 Â which is much dial distribution functions, RDF(r)'s, are shown
shorter than that of the melt-quenched glass, of in Fig. 10. Oscillation of S(Q) in a high-β region
40 Â or more. This implies that the connectivity of is clearly observed at all temperatures studied,
S1O4 structural units is considerably distorted in and the characteristics of the oscillation are sim-
sputter-deposited amorphous film compared with ilar to each other. The first two peaks, marked
the melt-quenched glass. Measuring S(Q) in a r\ and Γ2 in the RDF(r) curves, are essentially
very wide range of Q seems to be very impor- unchanged in the observed temperature range ex-
tant in the structural analysis of technologically cept for some broadening at higher temperatures.
interesting disordered materials. These observations imply that the structural units