Тhe competition of mott and frideel type stoppers as the main blocking mechanisms in mobile dislocations of KBr crystals
The experimental data of pulsed-method research in the frequency range 7.5...232.5 MHz of the preliminary deformation effect ε in the range of 0.23…1%, and at the temperature interval 77...300 K on the frequency spectra localization Δd(f) in the dislocation decrement of ultrasonic attenuation, as...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2018
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| Цитувати: | Тhe competition of mott and frideel type stoppers as the main blocking mechanisms in mobile dislocations of KBr crystals / О.M. Petchenko, G.О. Petchenko, S.M. Boiko // Вопросы атомной науки и техники. — 2018. — № 5. — С. 24-28. — Бібліогр.: 40 назв. — англ. |
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Petchenko, О.M. Petchenko, G.О. Boiko, S.M. 2019-02-15T17:51:51Z 2019-02-15T17:51:51Z 2018 Тhe competition of mott and frideel type stoppers as the main blocking mechanisms in mobile dislocations of KBr crystals / О.M. Petchenko, G.О. Petchenko, S.M. Boiko // Вопросы атомной науки и техники. — 2018. — № 5. — С. 24-28. — Бібліогр.: 40 назв. — англ. 1562-6016 https://nasplib.isofts.kiev.ua/handle/123456789/147695 539.67:539.374 The experimental data of pulsed-method research in the frequency range 7.5...232.5 MHz of the preliminary deformation effect ε in the range of 0.23…1%, and at the temperature interval 77...300 K on the frequency spectra localization Δd(f) in the dislocation decrement of ultrasonic attenuation, as well as on dynamic (B) and structural characteristics (L, Λ) of KBr crystals. The competition of strong and weak stoppers in the processes of blocking mobile dislocations in the investigated crystals is vividly traced. The limiting value of ε = 2.25% is established, above which the thermal activation of the mobile dislocations' detachment from Friedel type stoppers is completely masked by more efficient processes of fixing dislocations by dislocation network nodes (Mott stoppers), which gave us grounds to recommend performing of further studies in this direction. Проаналізовано експериментальні дані досліджень імпульсним методом у межах діапазону частот 7,5…232,5 МГц, а також їх вплив попередньої деформації ε у діапазоні 0,23…1% і температури в інтервалі 77…300 К на локалізацію частотних спектрів Δd(f) дислокаційного декременту поглинання ультразвуку та на динамічні (В) і структурні характеристики (L, Λ) кристалів KBr. Простежено конкуренцію сильних і слабких стопорів у процесах блокування рухливих дислокацій в досліджуваних кристалах. Встановлено граничне значення ε = 2.25%, вище якого термічна активація процесів відкріплення рухливих дислокацій від стопорів фриделівського типу повністю маскується більш ефективними процесами закріплення дислокацій вузлами дислокаційної сітки (стопорами Мотта), що дало підставу визначити рекомендації для подальших досліджень у цьому напрямку. Проанализированы экспериментальные данные исследований импульсным методом в области частот 7,5…232,5 МГц, а также их влияния предварительной деформации ε в диапазоне 0,23…1% и температуры в интервале 77…300 К на локализацию частотных спектров Δd(f) дислокационного декремента затухания ультразвука и на динамические (В) и структурные характеристики (L, Λ) кристаллов KBr. Отслежена конкуренция сильных и слабых стопоров в процессах блокировки подвижных дислокаций в исследуемых кристаллах. Установлено граничное значение ε = 2,25%, выше которого термическая активация процессов открепления подвижных дислокаций от стопоров фриделевского типа полностью маскируется более эффективными процессами закрепления дислокаций узлами дислокационной сетки (стопорами Мотта), что дало основание сделать рекомендации для дальнейших исследований в этом направлении. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Физика радиационных повреждений и явлений в твердых телах Тhe competition of mott and frideel type stoppers as the main blocking mechanisms in mobile dislocations of KBr crystals Конкуренція механізмів блокування рухливих дислокацій в кристалах KBr стопорами типу мотта і фриделя Конкуренция механизмов блокировки подвижных дислокаций в кристаллах KBr стопорами типа мотта и фриделя Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Тhe competition of mott and frideel type stoppers as the main blocking mechanisms in mobile dislocations of KBr crystals |
| spellingShingle |
Тhe competition of mott and frideel type stoppers as the main blocking mechanisms in mobile dislocations of KBr crystals Petchenko, О.M. Petchenko, G.О. Boiko, S.M. Физика радиационных повреждений и явлений в твердых телах |
| title_short |
Тhe competition of mott and frideel type stoppers as the main blocking mechanisms in mobile dislocations of KBr crystals |
| title_full |
Тhe competition of mott and frideel type stoppers as the main blocking mechanisms in mobile dislocations of KBr crystals |
| title_fullStr |
Тhe competition of mott and frideel type stoppers as the main blocking mechanisms in mobile dislocations of KBr crystals |
| title_full_unstemmed |
Тhe competition of mott and frideel type stoppers as the main blocking mechanisms in mobile dislocations of KBr crystals |
| title_sort |
тhe competition of mott and frideel type stoppers as the main blocking mechanisms in mobile dislocations of kbr crystals |
| author |
Petchenko, О.M. Petchenko, G.О. Boiko, S.M. |
| author_facet |
Petchenko, О.M. Petchenko, G.О. Boiko, S.M. |
| topic |
Физика радиационных повреждений и явлений в твердых телах |
| topic_facet |
Физика радиационных повреждений и явлений в твердых телах |
| publishDate |
2018 |
| language |
English |
| container_title |
Вопросы атомной науки и техники |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| title_alt |
Конкуренція механізмів блокування рухливих дислокацій в кристалах KBr стопорами типу мотта і фриделя Конкуренция механизмов блокировки подвижных дислокаций в кристаллах KBr стопорами типа мотта и фриделя |
| description |
The experimental data of pulsed-method research in the frequency range 7.5...232.5 MHz of the preliminary
deformation effect ε in the range of 0.23…1%, and at the temperature interval 77...300 K on the frequency spectra
localization Δd(f) in the dislocation decrement of ultrasonic attenuation, as well as on dynamic (B) and structural
characteristics (L, Λ) of KBr crystals. The competition of strong and weak stoppers in the processes of blocking
mobile dislocations in the investigated crystals is vividly traced. The limiting value of ε = 2.25% is established,
above which the thermal activation of the mobile dislocations' detachment from Friedel type stoppers is completely
masked by more efficient processes of fixing dislocations by dislocation network nodes (Mott stoppers), which gave
us grounds to recommend performing of further studies in this direction.
Проаналізовано експериментальні дані досліджень імпульсним методом у межах діапазону частот
7,5…232,5 МГц, а також їх вплив попередньої деформації ε у діапазоні 0,23…1% і температури в інтервалі
77…300 К на локалізацію частотних спектрів Δd(f) дислокаційного декременту поглинання ультразвуку та на
динамічні (В) і структурні характеристики (L, Λ) кристалів KBr. Простежено конкуренцію сильних і слабких стопорів у процесах блокування рухливих дислокацій в досліджуваних кристалах. Встановлено граничне значення ε = 2.25%, вище якого термічна активація процесів відкріплення рухливих дислокацій від стопорів фриделівського типу повністю маскується більш ефективними процесами закріплення дислокацій вузлами дислокаційної сітки (стопорами Мотта), що дало підставу визначити рекомендації для подальших досліджень у цьому напрямку.
Проанализированы экспериментальные данные исследований импульсным методом в области частот
7,5…232,5 МГц, а также их влияния предварительной деформации ε в диапазоне 0,23…1% и температуры в
интервале 77…300 К на локализацию частотных спектров Δd(f) дислокационного декремента затухания ультразвука и на динамические (В) и структурные характеристики (L, Λ) кристаллов KBr. Отслежена конкуренция сильных и слабых стопоров в процессах блокировки подвижных дислокаций в исследуемых кристаллах.
Установлено граничное значение ε = 2,25%, выше которого термическая активация процессов открепления
подвижных дислокаций от стопоров фриделевского типа полностью маскируется более эффективными процессами закрепления дислокаций узлами дислокационной сетки (стопорами Мотта), что дало основание
сделать рекомендации для дальнейших исследований в этом направлении.
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/147695 |
| citation_txt |
Тhe competition of mott and frideel type stoppers as the main blocking mechanisms in mobile dislocations of KBr crystals / О.M. Petchenko, G.О. Petchenko, S.M. Boiko // Вопросы атомной науки и техники. — 2018. — № 5. — С. 24-28. — Бібліогр.: 40 назв. — англ. |
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24 ISSN 1562-6016. ВАНТ. 2018. №5(117)
UDC 539.67:539.374
THE COMPETITION OF MOTT AND FRIDEEL TYPE STOPPERS AS
THE MAIN BLOCKING MECHANISMS IN MOBILE DISLOCATIONS
OF KBr CRYSTALS
О.M. Petchenko
1
, G.О. Petchenko
1
, S.M. Boiko
2
1
O.M. Beketov National University of Urban Economy in Kharkiv, Kharkov, Ukraine
E-mail: gdaeron@ukr.net;
2
M.Ye. Zhukovskiy Kharkiv National Aerospace University, Kharkov, Ukraine
E-mail: svitlanazagreba7@gmail.com
The experimental data of pulsed-method research in the frequency range 7.5...232.5 MHz of the preliminary
deformation effect in the range of 0.23…1%, and at the temperature interval 77...300 K on the frequency spectra
localization d(f) in the dislocation decrement of ultrasonic attenuation, as well as on dynamic (B) and structural
characteristics (L, ) of KBr crystals. The competition of strong and weak stoppers in the processes of blocking
mobile dislocations in the investigated crystals is vividly traced. The limiting value of 2.25% is established,
above which the thermal activation of the mobile dislocations' detachment from Friedel type stoppers is completely
masked by more efficient processes of fixing dislocations by dislocation network nodes (Mott stoppers), which gave
us grounds to recommend performing of further studies in this direction.
INTRODUCTION
The temperature behavior of the coefficient B was
attempted to study by many authors, both on metals, and
on ionic crystals [1–11]. The overwhelming majority of
these works were really performed in the form of
observing the individual dislocations' mobility, slip
bands, and also as the results of high-speed crystals'
deformation. The most reliable method [1–3], that
allows us to study the phonon-dislocation interaction in
crystals, the consideration of which is directly based on
the results of the temperature behavior study of the
parameter B, is the method of amplitude-independent
internal friction. In the works [12–17], the authors
managed to achieve quite reliable results due to which
the verification of the Granato-Lucke string dislocation
theory [1] and the quantum-mechanical theory of
dislocations' dynamic inhibition by Alshits-Indenbom
[2] was performed. The results [12–17] showed that the
dynamic inhibition of dislocations in the investigated
KBr crystals in the range 77...300 K is limited by the
superposition of two phonon mechanisms: the phonon
wind and the relaxation of “slow” phonons. The
influence of the samples' dislocation structure in the
range of the dislocation density variable
= 2,210
9
…1310
9
m
-2 on the absolute value of B and
its temperature course in the indicated thermal interval
was also studied. It turned out that for temperatures at
the interval from the nitrogen to the room one, constant
of the dislocations' dynamic breaking B does not depend
on the density of mobile dislocations in the
investigated crystals. The mentioned result is of utmost
importance, since none of the laboratories in the world
have studied the problem of the mobile dislocations'
density influence on the temperature variation of the B
value, and, hence, on the efficiency of the various
phonon mechanisms' action in crystals. The solution to
this problem and the experimental proof of the fact, that
the dynamic braking temperature course of dislocations
in crystals is unchanged in the variation of the
parameter , and it provides significant opportunities
for the further development of the dislocation theory
based on the generalization of experimental data
obtained in different laboratories on identical crystals.
The fact is that when preparing samples for research, all
scientific schools use their own materials and
experimental techniques, that's why there are some
inconvenience when trying to consider the experimental
results of various laboratories from a single angle of
view – the samples' chemical composition differs
greatly (the points of fixation at the dislocations),
various methods, conditions and equipment for growing
crystals (different levels of “growth” dislocations,
different technological schemes of samples' annealing,
speed modes' variability of deformation machines, etc.).
That is, all samples have a different dislocation
structure, own unique preparation “history”, and it is
difficult to compare and evaluate them according to a
single graduation. But works [12–17] showed that all
these dissimilitudes are completely insignificant for the
general picture of the dislocations' phonon braking in
crystals.
In the view of the theory effectiveness verifying [1],
the works [12–17] are useful, in general, because they
were performed on the basis of an experiment, the
formulation of which was carried out within the
framework of the model [1]. String model [1] provides
two types of pinning points – nodes of a dislocation grid
(Mott stoppers) and weaker centers of fastening (Friedel
stops). The removal from the Friedel stoppers
(impurities, in our case) occurs due to thermal or
mechanical (pre-deformation of crystals) activation. It
was the competition of these mechanisms that
determined the mobility of dislocations in our
experiments.
The purpose of this paper is to generalize the results
obtained in [12–17] for the boundaries of the model's
efficiency settlement [1] and to describe physical
processes of the dislocation mobility thermal activation
in crystals.
mailto:gdaeron@ukr.net
mailto:svitlanazagreba7@gmail.com
ISSN 1562-6016. ВАНТ. 2018. №5(117) 25
MATERIALS
AND EXPERIMENTAL TECHNIQUES
In works [12–17] we investigated the diminished
dislocation resonance in single crystals of KBr with
degrees of previous deformation = 0.23; 0.5; 0.75, and
1% in the temperature range 77...300 K using longitudi-
nal waves in the frequency range 7.5...232.5 MHz. The
precision measurements of the ultrasonic attenuation
were performed by the method of exponential overlay
on single crystals, oriented along the crystallographic
direction <100> at the apparatus [18]. The presence of
impurities in samples, detected by methods of chemical
and spectral analysis, was (weight %): Cu 10
-6
; Mn,
Ag 10
-5
; Pb, Mg, Al, Ti 10
-4
; Fe 10
-3
. From the
crystals grown by means of the Kiropoulos method,
prototype samples were made, the size of which was
approximately 18x18x30 mm. The samples' parameters
took into account the basic authors' recommendations
[19–21] regarding to the choice of their geometry – the
cross-section and the length of the crystal, which is sub-
ject to acoustic measurement. The flat-parity of the
samples corresponded to the recommendations [20] and
constituted ± 1 μm/cm, that was controlled by the opti-
meter IKB. The scheme of samples' annealing after ma-
chining to eliminate internal stresses was as follows:
heating crystals in a muffle furnace MP-2UM to a tem-
perature of 0.8∙Тm (for the investigated crystals – up to
600 °C), time elapsing at the given temperature, and
slow cooling at a rate of 10 °С/h. The duration of an-
nealing was about 15 hours. The temperature was con-
trolled by a chromel-aluminium thermocouple connect-
ed to a digital voltmeter V7-27. Technologies of defor-
mation and low-temperature measurements of samples
are minutely described in [12–17].
RESULTS AND DISCUSSION
The results of studies [12–17] on the influence of
temperature in the range 77...300 K on the behavior of
the frequency spectra of the dislocation absorption d (f)
of ultrasound in specimens with different residual de-
formation values and the resulting data with respect to
the comparison of the temperature velocity В(Т) calcu-
lated within the framework of the Granato-Lucke theory
[1] with the theoretical curve of Alshits-Indenbom [2],
that is shown in Fig. 1.
Fig. 1. Frequency dependences of the dislocation decrement for different temperatures of the interval 77...300 K
(1–3). Solid curves – theoretical profiles (1–5) [1, 22]; straight lines (1'–5 ') – their high-frequency asymptotes;
4 comparison of the combined temperature transition [2] B(T)/ B(θ) with experimental data for KBr crystal
(o – data of papers [12, 13]; ,, – data of works [14–17] for crystals of potassium bromide with deformations
= 0.5; 0.75, and 1%); curve 2 – high-asymptote; е – phenomenological parameter of the theory [2]
One can see (see Figs. 1.1–1.3) that the experimental
points for the curves d(f) are sufficiently well described
by the theoretical frequency profile obtained by the
authors [22] for the exponential distribution of the
dislocation segments in length, which is mentioned in
the theory [1]. Also, there is a tendency for the
frequency spectrum to be offset both in frequency – to
the direction of higher f, and in the amplitude – to the
10 100
1
10
10 100
1
10
6'
6
3
4
5
6, 6
'
- 90 K
5'
5, 5
'
- 120 K
4, 4
'
- 150 K
3, 3
'
- 200 K
2, 2
'
- 250 K
1
3'
1, 1
'
- 300 K
2'
2
1' 4'
10 100
1
10 100
1
10
10 100
1
10
.
d
f, MHz
10 100
1
10
10 100
1
10
10 100
1
10
10 100
1
10
10 100
1
10
10 100
1
10
10 100
1
10
10 100
1
10
10 100
1
10
10 100
1
10
5'
5
5, 5
'
- 77 K
4, 4
'
- 100 K
3, 3
'
- 150 K
2, 2
'
- 250 K
1 3'
1, 1
'
- 300 K
2'
2
4
1'
3
4'
10 100
1
10 100
1
10
10 100
1
10
.
d
f, MHz
1
10 100
1
10
10 100
1
10
10 100
1
10
6'
6
3
4
5
6, 6
'
- 77 K
5'
5, 5
'
- 100 K
4, 4
'
- 150 K
3, 3
'
- 200 K
2, 2
'
- 250 K
1
3'
1, 1
'
- 300 K
2'
2
1' 4'
10 100
1
10 100
1
10
10 100
1
10
.
d
f, MHz
1
10 100
1
10
10 100
1
10
10 100
1
10
10 100
1
10
10 100
1
10
10 100
1
10
10 100
1
10
0 1
0
1
0 1
0
1
0 1
0
1
е
2
1
B
(T
)/B
(
)
T/0 1
0
1
0 1
0
1
0 1
0
1
21
3 4
26 ISSN 1562-6016. ВАНТ. 2018. №5(117)
direction of smaller d when the temperature decreases
at the studied interval. It is also obviously seen
(see Fig. 1.4) that the variation in the samples'
deformation within the range of 0.23...1% does not lead
to changes in В(Т) and therefore does not affect the
process of mobile dislocations' phonon braking in the
investigated crystals. After the temperature After the
temperature course establishing В(Т) it became possible
to trace the thermal variations of the average effective
dislocation segment length L. The value L could be
determined with the help of the relations [1], minutely
described in papers [12–17]. The family of curves L(T)
for KBr crystals with dislocation density within the
interval of = (2.2…13)10
9
m
-2
, corresponding to the
deformations of the interval 0.23...1%, is shown in
Fig. 2.
Fig. 2. The temperature dependences of the average
effective dislocation segment length L for KBr crystals
with different dislocation density
One can see that the tendency to reduce the average
effective length of the dislocation segment with a
decrease in temperature for any value of residual
deformation of the sample is sustained. However, the of
the dependences' displacement at the height L(Т) under
conditions of deformation growth is non-monotonic.
Initially, with an increase in deformation from 0.23 to
0.5%, we observe the displacement of L(Т) in the area
of higher L values (see curves 1 and 2, Fig. 2, and then,
at deformations of 0.75 and 1%, the offset sign changes
to the opposite (see curves 3 and 4, Fig. 2). The given
family of curves L(Т) proves that the inversion shift of
the frequency spectra d (f) [12–17], caused by
deformation of the crystal is observed for all
temperatures of the interval 77...300 K. In a detailed
examination of these curves, it was noted that the pace
of their growth, along with the temperature, is different
for the crystals with various dislocation density. For the
crystals with deformations of 0.23 and 0.5% (see curves
1 and 2 in Fig. 2), the value L increases in the
temperature range by 1.35 times. Curve 3 corresponding
to KBr crystals with =0.75%, already has a slower
slope with a temperature rise of 1.31 times, and curve 4
for KBr with = 1% shows the slightest increase in L –
only 1.25 times. The presented tendencies have an
expected physical explanation. In the course of minor
deformations (up to 0.5%), only the primary sliding
surfaces are activated in the crystal, and the dislocations
have a noticeable effect of pinning with the weak
stoppers – point defects. At 0.75%, in the crystal,
secondary systems of sliding start to operate and the
motion of the dislocations begins to be limited, except
for the weak, stronger stops – the nodes of the
dislocation grid start their functioning. Here, the effects
of the dislocation interaction with the weak stoppers
begin to become less noticeable against the background
of a more effective dislocations' interaction effect. The
further increase in deformation makes this grid of
dislocations even more dense, so the effect of the
dislocations' interaction with the point centers of
blocking is masked to a greater extent. We can also
assume that in a very strongly deformed crystal, the
dependence of L(Т) can go almost parallel to the
abscissa axis. This will correspond to a strongly
dislocation crystal, whose length of the Franck grid is
close to the size of the dislocation segment, limited by
the point pinning centers.
Having processed our data within the framework of
Origin 6.0, we came to the conclusion that the growth of
L of L value in the course of increase in the degree of
crystals' KBr deformation, decreases according to the
linear law L = 1.45 – 0.2. Thus, with the value of the
crystals' preliminary deformation 2.25% L will be
1, that correspond to the zero growth of the dislocation
segment along with the temperature increase. Therefore,
we must state that the limit value 2.25% defines the
upper border of the deformation interval, in which it is
possible, in principle, to study experimentally the
competition of the Mott and Friedel stoppers' action
in the course of the dislocations blocking [1, 23, 24].
Above this limit the dislocations are fixed by the nodes
of the Franck grid, so that the process of their
detachment is not thermally activated in the range of the
studied temperatures 77...300 K.
It is most likely to fail checking this experimentally.
If we recall that at = 1310
9
m
-2
(1%) the curves d(f),
aimed for the low temperatures, have already begun to
get out of the 7.5…217.5 MHz range limits with their
falling branches. It can be predicted, that even if it will
be possible to remove the frequency spectrum for a
strongly deformed ( 2.25%) crystal at room
temperature, then it is not possible to speak of lower
temperature studies.
The analysis can be useful for researchers studying
the influence of various factors (irradiation [25–29],
magnetic processing and variable chemical composition
of samples [30–40]) on the mobility of dislocations in
crystals. The preliminary deformation of the
investigated samples is a mandatory procedure, since it
allows for the insertion of mobile (“fresh”) dislocations
into the crystal, but the value of must not exceed the
limit specified by us. Otherwise, all the mentioned
investigated facts will be completely masked by the
strong processes of blocking the mobile dislocations by
the dislocations of the “forest”.
CONCLUSIONS
On the basis of our analysis and generalization of the
data obtained in previous studies on KBr crystals [12–
17], it was established that the thermal activation of
mobile dislocations' removing from Friedel-type
stoppers of any physical nature is restricted by the limit
100 150 200 250 300
0,4
0,6
0,8
1,0
1,2
.
.
.
. 1 - = 2,2 10
9
m
- 2
2 - = 4,5 10
9
m
-2
4 - = 13 10
9
m
-2
3 - = 9 10
9
m
-2
1
2
4
3
L
,
1
0
-
6
m
T, K
100 150 200 250 300
0,4
0,6
0,8
1,0
1,2
100 150 200 250 300
0,4
0,6
0,8
1,0
1,2
100 150 200 250 300
0,4
0,6
0,8
1,0
1,2
100 150 200 250 300
0,4
0,6
0,8
1,0
1,2
ISSN 1562-6016. ВАНТ. 2018. №5(117) 27
values of the of the investigated crystals' previous
deformation. According to our estimates, this value is
2.25%. For ε, less than the specified limit value, the
effect of thermal activation can be noticeable and,
therefore, external factors influencing the dislocation
structure of crystals (irradiation, magnetic processing,
changeable chemical composition of samples) can be
investigated by studying of the thermal effect on the
unlocking of mobile dislocations by means of
appropriate stoppers. For from 2.25% or more, fine
structural experiments will become ineffective due to
the strong background of dislocations' blocking by the
dislocations of the “forest” and the masking of weak
Friedel-type pinning points' effect by strong Mott-type
stoppers [1].
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Статья поступила в редакцию 14.08.2018 г.
КОНКУРЕНЦИЯ МЕХАНИЗМОВ БЛОКИРОВКИ ПОДВИЖНЫХ ДИСЛОКАЦИЙ
В КРИСТАЛЛАХ KBr СТОПОРАМИ ТИПА МОТТА И ФРИДЕЛЯ
А.М. Петченко, Г.А. Петченко, С.Н. Бойко
Проанализированы экспериментальные данные исследований импульсным методом в области частот
7,5…232,5 МГц, а также их влияния предварительной деформации в диапазоне 0,23…1% и температуры в
интервале 77…300 К на локализацию частотных спектров d(f) дислокационного декремента затухания уль-
тразвука и на динамические (В) и структурные характеристики (L, ) кристаллов KBr. Отслежена конкурен-
ция сильных и слабых стопоров в процессах блокировки подвижных дислокаций в исследуемых кристаллах.
Установлено граничное значение 2,25%, выше которого термическая активация процессов открепления
подвижных дислокаций от стопоров фриделевского типа полностью маскируется более эффективными про-
цессами закрепления дислокаций узлами дислокационной сетки (стопорами Мотта), что дало основание
сделать рекомендации для дальнейших исследований в этом направлении.
КОНКУРЕНЦІЯ МЕХАНІЗМІВ БЛОКУВАННЯ РУХЛИВИХ ДИСЛОКАЦІЙ
В КРИСТАЛАХ KBr СТОПОРАМИ ТИПУ МОТТА І ФРИДЕЛЯ
О.М. Петченко, Г.О. Петченко, С.М. Бойко
Проаналізовано експериментальні дані досліджень імпульсним методом у межах діапазону частот
7,5…232,5 МГц, а також їх вплив попередньої деформації у діапазоні 0,23…1% і температури в інтервалі
77…300 К на локалізацію частотних спектрів d(f) дислокаційного декременту поглинання ультразвуку та на
динамічні (В) і структурні характеристики (L, ) кристалів KBr. Простежено конкуренцію сильних і слаб-
ких стопорів у процесах блокування рухливих дислокацій в досліджуваних кристалах. Встановлено гранич-
не значення 2,25%, вище якого термічна активація процесів відкріплення рухливих дислокацій від сто-
порів фриделівського типу повністю маскується більш ефективними процесами закріплення дислокацій вуз-
лами дислокаційної сітки (стопорами Мотта), що дало підставу визначити рекомендації для подальших дос-
ліджень у цьому напрямку.
28
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