Unusual morphology of equimolar Ar–Kr alloys
The transmission high electron energy diffraction (THEED) technique was employed for studying the structure of the equimolar Ar–Kr alloy, in which the thermodynamics predicts the maximum feasibility of phase separation. Deposition of preliminarily cooled gas mixtures was performed onto substrates...
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| Cite this: | Unusual morphology of equimolar Ar–Kr alloys / V.V. Danchuk, A.A. Solodovnik, N.S. Mysko, M.A. Strzhemechny // Физика низких температур. — 2015. — Т. 41, № 6. — С. 546-551. — Бібліогр.: 24 назв. — англ. |
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Danchuk, V.V. Solodovnik, A.A. Mysko, N.S. Strzhemechny, M.A. 2017-12-28T15:19:42Z 2017-12-28T15:19:42Z 2015 Unusual morphology of equimolar Ar–Kr alloys / V.V. Danchuk, A.A. Solodovnik, N.S. Mysko, M.A. Strzhemechny // Физика низких температур. — 2015. — Т. 41, № 6. — С. 546-551. — Бібліогр.: 24 назв. — англ. 0132-6414 PACS: 61.05.J–, 78.55.Kz, 61.66.Dk https://nasplib.isofts.kiev.ua/handle/123456789/127826 The transmission high electron energy diffraction (THEED) technique was employed for studying the structure of the equimolar Ar–Kr alloy, in which the thermodynamics predicts the maximum feasibility of phase separation. Deposition of preliminarily cooled gas mixtures was performed onto substrates cooled to 6 or 20 K. All diffraction patterns contained several sets of reflections against an appreciable background. Analysis of the data obtained during a warm-up from 6 to 33 K (at which the major part of argon was removed due to sublimation) as well as of the diffraction pattern from the “sandwich” (two successively deposited film of pure Ar and Kr) provided reliable arguments for the following conclusions. Actually, we have documented for the first time a phase separation of an Ar–Kr mixture, manifestations of which turned out to be oddly asymmetric as far as the behavior of the components involved is concerned. Upon deposition both onto 6 or 20 K the emerging sample contained two crystal phases of virtually pure argon with a small admixture of krypton. One of the Ar phases (fcc) did not cause a surprise, whereas the other was hcp with the a/c ratio close to the ideal value. The krypton component separated as a fine-grained glass-like state, possibly, with a low admixture of argon. The authors express their gratitude to A.V. Dolbin for the high-purity gases used in these studies. We also thank S.I. Kovalenko for critical reading of the manuscript. en Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України Физика низких температур 10th International Conference on Cryocrystals and Quantum Crystals Unusual morphology of equimolar Ar–Kr alloys Article published earlier |
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Unusual morphology of equimolar Ar–Kr alloys |
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Unusual morphology of equimolar Ar–Kr alloys Danchuk, V.V. Solodovnik, A.A. Mysko, N.S. Strzhemechny, M.A. 10th International Conference on Cryocrystals and Quantum Crystals |
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Unusual morphology of equimolar Ar–Kr alloys |
| title_full |
Unusual morphology of equimolar Ar–Kr alloys |
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Unusual morphology of equimolar Ar–Kr alloys |
| title_full_unstemmed |
Unusual morphology of equimolar Ar–Kr alloys |
| title_sort |
unusual morphology of equimolar ar–kr alloys |
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Danchuk, V.V. Solodovnik, A.A. Mysko, N.S. Strzhemechny, M.A. |
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Danchuk, V.V. Solodovnik, A.A. Mysko, N.S. Strzhemechny, M.A. |
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10th International Conference on Cryocrystals and Quantum Crystals |
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10th International Conference on Cryocrystals and Quantum Crystals |
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2015 |
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English |
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Физика низких температур |
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Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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The transmission high electron energy diffraction (THEED) technique was employed for studying the structure
of the equimolar Ar–Kr alloy, in which the thermodynamics predicts the maximum feasibility of phase separation.
Deposition of preliminarily cooled gas mixtures was performed onto substrates cooled to 6 or 20 K. All
diffraction patterns contained several sets of reflections against an appreciable background. Analysis of the data
obtained during a warm-up from 6 to 33 K (at which the major part of argon was removed due to sublimation) as
well as of the diffraction pattern from the “sandwich” (two successively deposited film of pure Ar and Kr) provided
reliable arguments for the following conclusions. Actually, we have documented for the first time a phase
separation of an Ar–Kr mixture, manifestations of which turned out to be oddly asymmetric as far as the behavior
of the components involved is concerned. Upon deposition both onto 6 or 20 K the emerging sample contained
two crystal phases of virtually pure argon with a small admixture of krypton. One of the Ar phases (fcc)
did not cause a surprise, whereas the other was hcp with the a/c ratio close to the ideal value. The krypton component
separated as a fine-grained glass-like state, possibly, with a low admixture of argon.
|
| issn |
0132-6414 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/127826 |
| citation_txt |
Unusual morphology of equimolar Ar–Kr alloys / V.V. Danchuk, A.A. Solodovnik, N.S. Mysko, M.A. Strzhemechny // Физика низких температур. — 2015. — Т. 41, № 6. — С. 546-551. — Бібліогр.: 24 назв. — англ. |
| work_keys_str_mv |
AT danchukvv unusualmorphologyofequimolararkralloys AT solodovnikaa unusualmorphologyofequimolararkralloys AT myskons unusualmorphologyofequimolararkralloys AT strzhemechnyma unusualmorphologyofequimolararkralloys |
| first_indexed |
2025-11-26T15:22:34Z |
| last_indexed |
2025-11-26T15:22:34Z |
| _version_ |
1850626283026776064 |
| fulltext |
© V.V. Danchuk, A.A. Solodovnik, N.S. Mysko, and M.A. Strzhemechny, 2015
Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 6, pp. 546–551
Unusual morphology of equimolar Ar–Kr alloys
V.V. Danchuk, A.A. Solodovnik, N.S. Mysko, and M.A. Strzhemechny
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine
47 Lenin Ave., Kharkov 61103, Ukraine
E-mail: danchuk@ilt.kharkov.ua
Received February 26, 2015, published online April 23, 2015
The transmission high electron energy diffraction (THEED) technique was employed for studying the struc-
ture of the equimolar Ar–Kr alloy, in which the thermodynamics predicts the maximum feasibility of phase sepa-
ration. Deposition of preliminarily cooled gas mixtures was performed onto substrates cooled to 6 or 20 K. All
diffraction patterns contained several sets of reflections against an appreciable background. Analysis of the data
obtained during a warm-up from 6 to 33 K (at which the major part of argon was removed due to sublimation) as
well as of the diffraction pattern from the “sandwich” (two successively deposited film of pure Ar and Kr) pro-
vided reliable arguments for the following conclusions. Actually, we have documented for the first time a phase
separation of an Ar–Kr mixture, manifestations of which turned out to be oddly asymmetric as far as the behav-
ior of the components involved is concerned. Upon deposition both onto 6 or 20 K the emerging sample con-
tained two crystal phases of virtually pure argon with a small admixture of krypton. One of the Ar phases (fcc)
did not cause a surprise, whereas the other was hcp with the a/c ratio close to the ideal value. The krypton com-
ponent separated as a fine-grained glass-like state, possibly, with a low admixture of argon.
PACS: 61.05.J– Electron diffraction and scattering;
78.55.Kz Solid organic materials;
61.66.Dk Alloys.
Keywords: electron diffraction, Ar–Kr alloys, morphology.
1. Introduction
Rare gas binary alloys are suitable objects for investiga-
tion into basics of solid state [1]. These systems can be
consistently described using the Lennard-Jones pairwise
potential, which enables a proper testing of relevant theo-
retical approach, in particular, data concerning liquid and
solid rare gas mixtures formed a basic of the theory dealing
with formation and stability of binary mixtures. According
to Prigogine [2], for any composition of a solid binary so-
lution there is a critical temperature, below which phase
separation is possible. This critical temperature is highest
for equimolar solutions. Structure studies of Ar–Kr alloys
at liquid helium temperatures [3,4] gave evidence of com-
plete mutual solubility which contradicts basic thermody-
namics laws. Arguments for the statement of mutual solu-
bility in the solid over the entire composition range were
based on the observation that the composition dependence
of the lattice parameter agrees well with Vegard’s and Pri-
gogine's rules. First evidence for incomplete solubility in
Ar–Kr alloys was documented in neutron scattering studies
[5]. Analysis brought the authors to the conclusion that the
Kr matrix contains Ar clusters, which means that the infer-
able of the complete solubility of both components has to
be but to doubt. The boson peak discovered in calorimetric
studies on the Kr–25%Ar alloy [6] was another evidence
against the homogeneity of Ar–Kr alloys within the entire
range of mutual concentrations. A similar conclusion about
the complete solubility was made for the N2–Ar alloys (a
close analog of the Ar–Kr system) [7,8]. However in later
investigations [9,10] the separation boundaries have been
determined for this binary system. The principal discrep-
ancy between the conclusions of the two groups concern-
ing the N2–Ar alloys can be explained by the differences in
sample preparation conditions and procedures.
It should be remarked that it is the possibility to vary in
a controlled way the morphology of emerging samples by
small changes in preparation conditions that constitutes the
basis of the present day methods employed in synthesizing
nanostructured materials [11]. One of the physical methods
used for preparation of nanostructures is by direct deposi-
tion. It is this method that we employed as the preparation
technique for growing Kr–Ar cryoalloys over the entire
Unusual morphology of equimolar Ar–Kr alloys
Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 6 547
range of mutual concentrations and within a broad range of
varying deposition parameters. In this paper we present
results of transmission high energy electron diffraction
(THEED) studies of Kr–Ar samples grown from equimolar
gas mixtures preliminarily cooled on their way along the
feeding tube kept at temperatures slightly below the liquid-
nitrogen point (sub-LN temperatures) and show that their
morphology differs drastically from, that of a regular alloy.
2. Experimental
Argon–krypton alloys were studied using the THEED
method on a EG-100A electron diffraction setup equipped
with a liquid-helium cryostat. Samples were prepared di-
rectly inside the working column by deposition gas mix-
tures of known composition onto a cooled substrate film
[12]. The gases were mixed in a special bottle at room
temperature, the typical mutual diffusion time according to
the Einstein-Smoluchowski relations amounted to 21 s.
Therefore, the typical waiting time of up to 5 minutes at
room temperature ensured a uniform distribution of the
gases. The net pressure in the bottle did not exceed
12 Torr. The actual composition was calculated from the
initial partial pressures of the components. Preparation of
samples was carried out using very small amounts (less
than 0.5 cm
3
) of the gas mixture; leak-in was performed in
the laminar regime. The design of the cryoshields allowed
variations of the inlet tube temperature from room to sub-
LN, which helped us to vary the morphology of emerging
deposits within a broad range.
Gas mixtures were deposited onto a polycrystalline al-
uminium substrate. The overall level of impurities in the
source argon and krypton gases did not exceed 0.01%.
When samples grew to a large-grain and homogenous
films, the lattice parameter error was below 0.1%. The
samples were grown by depositing equimolar Ar–Kr gas
mixtures onto a film substrate cooled down to 6 or 20 K,
the tip of the filling tube being kept at sub-LN temperature.
The THEED patterns were recorded on photo plates ei-
ther after the sample was deposited at a proper temperature
or during a subsequent heating of the samples up to the
relevant sublimation temperatures. The duly developed
patterns were digitized using a CanoScan 9950F scanner
with resolution 1200 dpi, the maximum optical density of
the scanner being 3.8 D. Digitized THEED patterns were
processed using Figi ImageJ package. The average size of
coherent scattering regions was evaluated using the true
diffraction line broadening [13] with account of stacking
faults [14,15] and making use of the Selyakov–Scherrer
relationship [16] for globular crystallites, which enabled us
to deal with mean grain sizes. The stacking fault density
was evaluated from the shifts of diffraction peaks respec-
tive their “reference” positions calculated from the position
of line 311 [17].
3. Results and discussion
Deposition of sub-LN equimolar Ar–Kr gas mixtures
onto a 6 K substrate resulted in polycrystalline weakly tex-
tured layers as shown in Fig. 1. We failed to determine the
structure and morphology of this sample within a mono-
phase assumption. Besides the reflections with inter-plane
distances 3.062, 2.656, 1.882, and 1.602 Å, which corre-
spond to indices, respectively, (111), (200), (220), and
(311) of a fcc Ar structure with a lattice parameter of
5.323 Å, the pattern contained reflections at small angles
with inter-plane distances d1 = 3.249 Å (S1 = 1.934 Å
–1
)
and d2 = 2.854 Å (S2 = 2.201 Å
–1
), which needed a special
analysis. It should be noted here that reflex d2, because of
its low intensity and large spread, was identified poorly so
that its very existence caused doubt. In Fig. 2 we present a
densitogram of the pattern plotted in Fig. 1. Subtraction of
the noncoherent background revealed that, apart from re-
flections fcc Ar and dn, the pattern includes a rather inten-
sive halo at small diffraction angles around S = 2.16 Å
–1
.
Let us discuss available possibilities to explain the dn sys-
tem and the halo.
Assumption 1: the dn reflection belong to a Kr-rich fcc
phase (reflections (111) and (200), respectively). If so, d1
yields the lattice parameter 5.627 Å, which could belong to
a Kr–10%Ar alloy. Reflection d2 corresponds to a =
= 5.719 Å, which by 0.05 Å exceeds the value for pure
krypton fcc (aKr = 5.67 Å). Subsequent annealing of this
sample up to 20 K entailed brightening of dn reflections.
The weak texture of the sample helped to “backlight” the
small-angle reflections, which allowed undoubted detec-
tion and localization of the d2 (Fig. 3).
The evident inconsistencies (positions and intensities)
of the dn reflections as representing the above-mentioned
Kr-rich phase, as well as the absence of the reflection with
d3 = 1.709 Å (S3 = 3.676 Å
–1
), which is characteristic of
the Kr (311) reflection, constitute a solid argument for the
claim that the dn system cannot belong to a krypton-rich
fcc phase. A clear example how two fcc structures overlap
is the pattern in Fig. 4 from the Ar–Kr “sandwich”. This
“sandwich” sample was produced in the following way.
Fig. 1. (Color online) Diffraction pattern of equimolar Ar–Kr
sample. Deposition and registration temperatures are 6 K.
V.V. Danchuk, A.A. Solodovnik, N.S. Mysko, and M.A. Strzhemechny
548 Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 6
First, a pure krypton film was deposited at 20 K, then
above it a pure argon film. In Fig. 4 the fcc peaks of both
Ar and Kr fcc phases nicely separate; the (111)/(200) in-
tensity ratios agree, within a small error, with the calculat-
ed values for fcc phases of Ar and Kr. Notice that the fcc
Kr reflections are brighter than those of the Ar phase,
which correlates with the atomic Ar/Kr scattering factor
ratio.
Assumption 2: dn reflections are due to secondary dif-
fraction from growth twin boundaries. In principle, the dn
reflections in Figs. 2 and 3 could be explained as a results
of secondary diffraction from growth twins [18]. Making
use of the shifts of the (111) and (200) peaks of the argon-
rich phase from their reference positions relative to the
(311) reflection we evaluated the deformational and
growth stacking fault densities [14,15]. The rather small
fault density parameters ( 0.015 and 0.06) are insuf-
ficient to ensure formation of an extra reflection. Another
independent argument against the assumption under dis-
cussion is the presence of the d2 peak, which does not ap-
pear due to boundary diffraction [18].
Assumption 3: dn reflections are formed by the hcp
phase of almost pure Ar. Upon indexing d1 and d2 as (100)
and (101) reflections of the hcp phase and taking into ac-
count the inevitable superposition of reflections (111) and
(002) from, respectively, the fcc and hcp phases we have
calculated the hcp lattice parameters to be: a = 3.752 Å,
c = 6.104 Å, c/a = 1.630. These values are somewhat larg-
er than those for pure argon, which is owing presumably to
the presence of some atoms of krypton in the Ar hcp phase.
The (102) reflection of the hcp argon phase is superim-
posed on the Al reference reflection (111) (which can be in
general absent). Van de Waal et al. [19] presented a model
diffraction pattern from a hcp polycluster of eight disori-
ented domains. Account of the intensity scattered from
inter-grain boundaries entailed suppression of certain hcp
lines and, in particular, disappearance of line (102). The
calculated spectra [19] were compared with experimental
diffraction data for free argon clusters to show that in some
cases the (102) reflection is not necessary for the identifi-
cation of hcp phases. Formation of hcp phase together with
the prevailing fcc phase as a consequence of annealing of
cold-deposited pure Ar and Ne films at temperatures close
to sublimation had been documented by Kovalenko and
Bagrov [14].
In Fig. 5 we show a diffraction pattern from a sample of
grown from sub-LN argon on a substrate at 20 K. Only the
fcc reflections are present, the lattice parameter being a =
= (5.322 0.005) Å. The stacking fault densities = 0.018
and = 0.059 are comparable with those in the equimolar
Ar–Kr samples. It is more interesting that the average grain
size in pure Ar about 70 Å, as evaluated with account for
stacking faults, is by a quarter less than the grain size of
the fcc phase in the equimolar samples, about 100 Å. This
is presumably a consequence of a higher mobility of argon
atoms in the crystallizing layers due to the elevated latent
heat of the krypton in the equimolar samples. In addition,
the very crystal growth mechanisms during deposition of
Fig. 2. (Color online) The diffracted intensity versus diffraction
parameter S = 4 sin / ( is the Bragg angle and is the electron
wave length) for the pattern in Fig. 1.
Fig. 3. (Color online) Densitogram of annealed equimolar Ar–Kr
sample deposited on 6 K and registered at 20 K.
Fig. 4. (Color online) Densitogram of the Ar–Kr sandwich.
Unusual morphology of equimolar Ar–Kr alloys
Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 6 549
the equimolar Ar–Kr mixtures and the pure argon differ.
For pure Ar the nucleus formation mechanism is mostly
homogeneous. But during deposition of Ar–Kr mixtures,
the krypton atoms and small clusters can serve as conden-
sation centers for Ar atoms. Therefore, nucleation mecha-
nism will be basically heterogeneous and, as a conse-
quence, the coherent scattering entities will have larger
sizes.
After the equimolar samples were heated up to 20 K,
the grain size of the fcc phase (about 90 Å) stayed actually
unchanged while the grain size of the hcp phase grew up
almost by one third, from 75 to 110 Å, making the relevant
reflections more distinct (cf. Fig. 3).
Deposition of a sub-LN Ar–Kr equimolar gas mix onto a
"warm" substrate at 20 K resulted in samples with patterns
like shown in Fig. 6. The fcc reflections grew brighter and
sharper compared to cold-deposited samples, the mean grain
size (of about 105 Å) are eventually the same as in cold-
deposited equimolar samples. It is noteworthy that stacking
faults in “warm”-deposited samples are denser: we evaluat-
ed the fault parameters to be = 0.064; = 0.087 (we re-
mind that in cold-deposited samples these quantities were
0.015; 0.06). This seeming paradox can be ex-
plained as follows: it is known that hcp nuclei in a fcc matrix
are, in particular, stacking faults. Therefore, since the hcp
fraction in cold-crystallized samples is higher than in warm-
deposited samples, a larger amount at stacking faults are
“eaten up” by the hcp regions present.
Analysis of the diffraction pattern in Fig. 6 unambigu-
ously indicates presence of reflections which are character-
istic of a hcp structure. It is well known that the diffraction
intensity is proportional to the scattering volume, which
allows estimation of the hcp/fcc ratios in our samples. The
ratio R = I101/I200 in warm-deposited samples R = 1.33
turns out to be below the corresponding estimate for cold-
deposited sample where R = 1.81, that is, the amount of
hcp in warm-deposited samples is smaller than in cold-
deposited ones. The overage hcp grain size in warm-
deposited sample was estimated to be 116 Å or, in other
word, it is the same within the error with the hcp grain size
in cold-deposited sample after it was warmed up to 20 K.
The fact that higher stacking faults in the fcc phase in sam-
ples with lower hcp contents correlates with the similar
conclusions for large free argon clusters [20]. The above-
stated fact, viz., the data concerning deposition of sub-LN
argon as well as sub-LN equimolar Ar–Kr mixtures onto
the substrate at 20 K give us grounds to the assert that it is
the presence of krypton in the mix that qualitatively influ-
ences the morphology of the emerging hcp grains during
deposition of sub-LN equimolar Ar–Kr mixtures. The sub-
strate temperature plays a subsidiary role.
The only question left unresolved is where krypton,
which constitutes half of the gas mixture deposited, “dis-
appears”. According to rough estimates, both (fcc and hcp)
crystal phases contain krypton in amounts less than 10
mol%. To answer this question, both cold – deposited and
warm-deposited samples were heated further. Within the
argon sublimation range, from 30 to 32 K, the peaks in
diffraction patterns disappeared, resulting in a pattern like
that shown in Fig. 7. The densitogram contains diffraction
peaks from the aluminum reference (substrate) with a halo
around S = 1.97 Å
–1
. Since at 33 K argon had been re-
moved, its characteristic crystal lines are absent. Further
warmup to 40 K resulted in a narrowing of the halo feature
as well as in appearance (against that background) of a
weak fcc reflections (111) and (311) of pure krypton. Sub-
sequent warmup to 42 K entailed a “sweeping” of the sub-
strate, leaving in the diffraction pattern only reflections,
which belong to fcc aluminum. The above heating-
provoked transformation was identical both for cold-
deposited and warm-deposited samples. Thus, the above-
mentioned halo is directly related with the krypton con-
tained in the pre-cooled gas mixture. A quite similar situa-
tion with the “disappearance” of one of the components
from coherent part of the diffraction pattern was observed
in experiments [21] with Kr-CO2 alloys. The correspond-
Fig. 5. (Color online) Densitogram of pure Ar deposited and regis-
tered at 20 K.
Fig. 6. (Color online) Diffraction pattern from an equimolar Ar–Kr
sample grown and registered on a “warm” substrate at 20 K.
V.V. Danchuk, A.A. Solodovnik, N.S. Mysko, and M.A. Strzhemechny
550 Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 6
ing analysis led to the conclusions that the “lost” compo-
nent (carbon dioxide) was present in the form of ultra-
dispersed inclusions. Such morphology is typical of disper-
sion hardened alloys; nanosize inclusions become a factor
that determines unique physical properties of these novel
materials [22].
As known, the very procedure of the best choice for the
functions that describe the profiles of the patterns can pro-
vide information concerning the morphology of the entities
under study [23]. According to Guinier [16], the appropri-
ate function to approximate diffraction peaks in an ideal
crystal is the Gauss function. It turned out that the shapes
of the peaks discussed in this article (Figs. 4 through to 7)
the best fitting function within the 1.5 Å
–1
S 2.5 Å
–1
range was the Lorentzian whereas the fcc peak (220) and
all reference peaks are described best by the Gaussian.
Analysis of the shapes of diffraction peaks from free argon
clusters [24] led to a conclusion that the Lorentzian shape
associates with higher densities of micro distortions caused
by the icosahedron ordering in small argon cluster, the
presence of five-fold symmetry, etc.
Unlike the pattern from pure argon (cf. Fig. 5), the
smaller-angle part of which, namely, reflections (111)
and (200), fit well the Lorentzian shape, the fitting of the
pattern from equimolar samples necessitates modelling
not only the four coherent reflections but also the halo. In
Fig. 8 we show how this halo transforms with increasing
temperature (the intensities are not related to one another).
The preparation procedure virtually did not affect the posi-
tion and width of the halo (the solid dotted curves in Fig. 8).
The average grain sizes were close to 10 Å. After argon was
removed by warming to 33 K, the center of halo (green tall-
est curve) moved from S = 2.16 Å
–1
to S = 1.97 Å
–1
, i.e.,
close to the position of the fcc (111) peak from pure kryp-
ton. It is noteworthy that after argon purging the halo grew
evidently broader. Therefore, in addition to krypton atoms,
argon atoms also participate in the formation of the halo.
Conclusions
The samples of argon-krypton alloys studied by
THEED were prepared by direct deposition of equimolar
gas mixtures, preliminarily cooled (as explained above),
onto substrates at 6 and 20 K. The entire set of reflections
in all diffraction patterns could not be interpreted as be-
longing to any unique space group. Analysis showed that
the diffraction pattern contains reflections from two crys-
talline phases (a fcc Ar–5% Kr solution and a hcp phase of
almost pure argon) and a broad halo, which corresponded
to a glass-like phase of almost pure krypton. Summing up,
we managed for the first time to prepare a situation to en-
sure a phase separation of an equimolar argon-krypton
alloy. The unexpected result was the fact that the separated
phases possessed crucially different morphologic forms:
the krypton-rich phase was basically in a nanocrystalline
(amorphous) state, whereas the predominantly argon-
containing phase included two crystalline states, fcc and
hcp.
The authors express their gratitude to A.V. Dolbin for
the high-purity gases used in these studies. We also thank
S.I. Kovalenko for critical reading of the manuscript.
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Academic Press, London, (1976) vol. 1; (1977) vol. 2.
2. I. Prigogine, The Molecular Theory of Solutions, North-
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