Plasticity of parahydrogen with reduced deuterium contents
The plasticity of solid parahydrogen with lowered deuterium contents under step-wise uniaxial extension at liquid helium temperatures 1.8–4.2 K has been investigated. Work hardening curves for single crystals have been measured. Maximum possible values of sample’s elongation without their fracture...
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irk-123456789-1217852017-06-17T03:03:14Z Plasticity of parahydrogen with reduced deuterium contents Alekseeva, L.A. Quantum Crystals The plasticity of solid parahydrogen with lowered deuterium contents under step-wise uniaxial extension at liquid helium temperatures 1.8–4.2 K has been investigated. Work hardening curves for single crystals have been measured. Maximum possible values of sample’s elongation without their fracture at minimum stress values have been reached. Features of super-plastic irreversible deformation of samples were observed. Anomalous temperature dependence of deformation parameters has been found. The character of this anomaly exhibits evidence of the coherent motion of dislocation kinks in Pierls relief, modified by residual ortho- and deuterium impurities. 2007 Article Plasticity of parahydrogen with reduced deuterium contents / L.A. Alekseeva // Физика низких температур. — 2007. — Т. 33, № 6-7. — С. 673-675. — Бібліогр.: 17 назв. — англ. 0132-6414 PACS: 62.20.–x; 67.80.–s http://dspace.nbuv.gov.ua/handle/123456789/121785 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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Quantum Crystals Quantum Crystals Alekseeva, L.A. Plasticity of parahydrogen with reduced deuterium contents Физика низких температур |
| description |
The plasticity of solid parahydrogen with lowered deuterium contents under step-wise uniaxial extension
at liquid helium temperatures 1.8–4.2 K has been investigated. Work hardening curves for single crystals
have been measured. Maximum possible values of sample’s elongation without their fracture at minimum
stress values have been reached. Features of super-plastic irreversible deformation of samples were
observed. Anomalous temperature dependence of deformation parameters has been found. The character of
this anomaly exhibits evidence of the coherent motion of dislocation kinks in Pierls relief, modified by residual
ortho- and deuterium impurities. |
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Article |
| author |
Alekseeva, L.A. |
| author_facet |
Alekseeva, L.A. |
| author_sort |
Alekseeva, L.A. |
| title |
Plasticity of parahydrogen with reduced deuterium contents |
| title_short |
Plasticity of parahydrogen with reduced deuterium contents |
| title_full |
Plasticity of parahydrogen with reduced deuterium contents |
| title_fullStr |
Plasticity of parahydrogen with reduced deuterium contents |
| title_full_unstemmed |
Plasticity of parahydrogen with reduced deuterium contents |
| title_sort |
plasticity of parahydrogen with reduced deuterium contents |
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Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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2007 |
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Quantum Crystals |
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http://dspace.nbuv.gov.ua/handle/123456789/121785 |
| citation_txt |
Plasticity of parahydrogen with reduced deuterium contents / L.A. Alekseeva // Физика низких температур. — 2007. — Т. 33, № 6-7. — С. 673-675. — Бібліогр.: 17 назв. — англ. |
| series |
Физика низких температур |
| work_keys_str_mv |
AT alekseevala plasticityofparahydrogenwithreduceddeuteriumcontents |
| first_indexed |
2025-07-08T20:31:11Z |
| last_indexed |
2025-07-08T20:31:11Z |
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1837112149254602752 |
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Fizika Nizkikh Temperatur, 2007, v. 33, Nos. 6/7, p. 673–675
Plasticity of parahydrogen with reduced deuterium contents
L.A. Alekseeva
B. Verkin Institute for Low Temperature Physics and Engineering National Academy
of Sciences of Ukraine, 47 Lenin Ave., Kharkov 61103, Ukraine
E-mail: alekseeva@ilt.kharkov.ua
Received September, 2006
The plasticity of solid parahydrogen with lowered deuterium contents under step-wise uniaxial exten-
sion at liquid helium temperatures 1.8–4.2 K has been investigated. Work hardening curves for single crys-
tals have been measured. Maximum possible values of sample’s elongation without their fracture at mini-
mum stress values have been reached. Features of super-plastic irreversible deformation of samples were
observed. Anomalous temperature dependence of deformation parameters has been found. The character of
this anomaly exhibits evidence of the coherent motion of dislocation kinks in Pierls relief, modified by re-
sidual ortho- and deuterium impurities.
PACS: 62.20.–x Mechanical Properties of Solids;
67.80.–s Solid Helium and Related Quantum Crystals.
Keywords: hardening curve, yield-stress, coherent band, dislocation kink, fracture.
Introduction
Due to delocalization of the wave function, the parti-
cles that form a quantum (including parahydrogen) crys-
tal are able to penetrate by tunneling through potential
barriers, separating one equilibrium position in the lattice
from another [1]. A possible crossover of a quantum crys-
tal to a state with zero static shear modulus [2] can be ob-
served by measuring its plasticity.
Pure p-H2 is a very plastic material down to 1.8 K, i.e.,
about 1% of the Debye temperature [3]. It's deformation
is brought about by extremely small loads [4–6]* and can
be interpreted more adequately in åðó quasi-particle ap-
proach. Isotopic impurities affect considerably the quan-
tum nature of hydrogen crystal flow. Unlike the soft pure
material, p-H2 doped with its stable deuterium isotope ex-
hibit a considerable strengthening and a much lower plas-
ticity [4,5,8]. Some other intriguing findings [6,9] on
very pure p-H2 were tentatively interpreted as being
related with large-scale planar defects**, viz., pseudo-
twins [9,10]. In view of this strong influence of isotopes,
it would be nice to have a method enabling the purifica-
tion of p-H2 in situ in order to obtain more perfect
samples. In this work a new method is suggested for pre-
paring single crystals of p-H2 with reduced isotope con-
tents.
Experimental
Pure p-H2 was produced from normal hydrogen (n-H2,
75% o-H2), purified in a SHPV-500 reactor, according to
the reactor certificate, to a level with less than 1 ppm of
non-hydrogen impurities. The o-H2 fraction was further
reduced to � 0.2% by keeping n-H2 long enough in the
presence of Fe(OH)3 at the H2 boiling temperature.
Part of p-H2 was crystallized in a modified he-
lium-cooled cell of the cryostat [11]. The crystallization
completed, electric power was fed to reheat the cell again
to T � 15 K. After the sample melted, part of the p-H2 va-
por was redirected back to the converter. As a result of the
difference between the partial pressures of deuterium and
hydrogen, the contents of the less volatile component is
© L.A. Alekseeva, 2007
* Our earlier results on the gravity-related low-temperature flow of the crystal [5] are at variance with subsequent experiments [6,7].
** Occurrence of these planar defects in HCP p-H
2
is caused by the small energy difference between HCP and FCC structures.
naturally reduced, thereby enriching the more volatile
component. Single-crystalline samples were grown from
pure vapor above the p-H2 distillate after double rectifica-
tion at a rate of � 0.3–0.5 mm/min; the final heavier iso-
tope fraction was considerably reduced (to [D]/[H]
~0.005–0.006%) compared to its natural abundance
([D]/[H] � 0.0147–0.0156% [12]). The considerable re-
duction of the isotope contents has been confirmed to
within 30 ppm by numerous isotope analyses by a modi-
fied MX-7304 mass spectrometer.
Transparent single-crystalline samples thus grown
were separated from cell walls by pumping off the vapor
over them, then annealed near the melting-point for
40–50 min and cooled slowly down to the test tempera-
ture.
Loading of samples was done with the aid of a 200 mG
sensitive balance scales. Crystal elongations were mea-
sured by the inductance displacement sensor with an ac-
curacy of � �
�1 10 5 cm, the temperature was measured with
semiconductor thermometers to within 20 mK.
Results and discussion
Since planar defects can be easily identified [13], sam-
ples were first load–relieve cycle tested. Figure 1 presents
a typical dependence of the relative elongation � on the
applied stress �. This stress-strain curve � �( ) was ob-
tained by a stepwise stretching. A fully irreversible char-
acter of deformation (no hysteresis observed) implied ab-
sence of large-scale planar defects. Reverse movement of
the rod resulted in loop-like macroscopic deformations
resembling observed earlier [5]
Figure 2 presents initial stages of the � �( ) curves,
which correspond to the boundary temperatures studied
(T = 4.2 and 1.8 K). The strain � here is limited along the
horizontal axis by the lowermost value observed (� 50%)
in experiment. Every crystal was tested (without fracture)
only at one temperature. Depending on the temperature
value, 7 to 9 crystals were examined. The two � �( ) curves
in Fig. 1 plotted from data obtained on those samples
which showed maximum strain at minimum stress, which
correspond to the most favourable orientation of the basal
HCP plane relatively to the stretching axis. The second
longer (almost linear) stages (not shown in Fig. 2) are
characterized by small of strengthening coefficients
� � �� d d/ and by minimum stresses � 0 of the stage to
stage crossover. The � values, normalized to the shear
modulus of solid p-H2 [3] were 3 10 5
�
� and 2 5 10 5. �
� at 4.2
K and 1.8 K, respectively. Such low values of � are typical
of the developed flow stage of the materials with HCP
structure [14], including p-H2 single crystals [5]. They
demonstrate that the p-H2 deformation occurs due to dis-
location displacements in any one of the possible crystal-
lographic planes [14]. It is interesting that the � �( ) curve
in Fig. 2 for the lower T is below the curve for the higher
T, which contradicts the standard notion of thermally acti-
vated deformation processes. The same concerns the � 0
versus T relation. The anomalous character of the yield
stress is evidence that quantum tunneling mechanisms
definitely prevails over classical thermally activated pro-
cesses. For comparison, � �( ) curves measured under com-
pression of single crystals of p-H2 at 2 K and 4.2 K [6] are
also shown in Fig. 2. Note that quite small stresses are
needed to obtain of comparatively great (� 3–7%)
strains. But further compression leads to a strong
strengthening of samples. It is possible that the twins (or
other packing faults), which are presumably responsible
for the hysteresis first observed in Ref. 6, lead to the
strong hardening in their samples. It should be remarked
that their samples were extremely pure if ortho-and iso-
tope impurities are concerned but contained much more
(20 ppm) non-hydrogen impurities, which are capable of
influencing crucially the plasticity of solid hydrogen.
674 Fizika Nizkikh Temperatur, 2007, v. 33, Nos. 6/7
L.A. Alekseeva
0
2 4 6 8 10 12 14 16
�, %
70
60
50
40
30
20
10
�
,
k
P
a
Fig. 1. Typical � �( ) obtained during load–relieve cycling for
p-H2 ([D]/[H] � 50–60 ppm) at T = 4.2 K.
1
2
3
100
80
60
40
20
0
�
,
k
P
a
2 4 6 8 10 12 14 16 18 20 22
0
2 4 6 8
8
4
1
T = 2 K
�, %
�
,
k
P
a
�, %
T = 4.2 K
4
Fig. 2. Typical � �( ) curves, measured on single crystals of
parahydrogen: curves 2 and 3 are data of this work (o-H2 �
� 0.2%, [D]/[H] � 50–60 ppm, nonhydrogen impurities 1 ppm;
T � 4.2 K (2), T = 1.8 K (3); curves 1 and 4 are compression data
[6] for 2 K and 4.2 K for super-pure p-H2 (o-H2 � 0.01–0.005%,
[D]/[H] � 1/5–1/7 of the natural abundance, nonhydrogen impuri-
ties ~ 0.002%).
Thus, the data presented here suggest that the plastic
flow is provided by individual dislocations moving
through the lattice via some tunneling mechanism, like it
was claimed in Ref. 5. Our present results give also evi-
dence that an important role in plastic flow belongs to mi-
croscopic defects (vacancies and dislocation kinks) and
their coherent band motion.
Since our samples contained low ortho-fractions
(about 0.2%), the number of pairwise ortho-clusters that
can interact significantly with moving dislocations (see
[15]) was small number (of the order of 2 10 6
�
� ). There-
fore, the main obstacle for dislocation motion was the
Pierls relief, modified by the deuterium impurities, which
might be efficient stoppers.
Summing up, the main agent that provides the disloca-
tion motion in the p-H2 crystals studied is, most likely,
dislocation kink [16,17]. The anomalous character of the
temperature dependency of both the yield stress � 0( )T
and the hardening coefficient is evidence of a band-like
character of their motion.
The author thanks M.A. Strzhemechny, K.A. Chishko,
A.I. Prokhvatilov, and V.D. Natsik for the discussions of
our results, D.N. Kazakov (Moscow, Russia) for numer-
ous mass-spectrometric and chromatographic analyses,
L.A. Vashchenko and T.Ph. Lemzyakova for chromato-
graphic analysis, and A.V. Kuznetsov for helping with ex-
periments.
1. A.F. Andreev and I.M. Lifshits, Zh. Eksp. Teor. Fiz. 56,
2057 (1969) [Sov. Phys. JETP 29, 1107 (1969)]; A.F.
Andreev, Usp. Fiz. Nauk 118, 251 (1976) [Sov. Phys. Usp.
19, 137 (1976)].
2. I.M. Lifshits, Fiz. Nizk. Temp. 1, 896 (1975) [Sov. J. Low
Temp. Phys. 1, 429 (1975)].
3. Physics of Cryocrystals, V.G. Manzhelii, Yu.A. Freiman,
M.L. Klein, and A.A. Maradudin (eds.), AIP Press,
Woodbury, New York (1996).
4. I.N. Krupskii, A.V. Leont’eva, L.A. Indan, and O.V.
Evdokimova, Pis’ma Zh. Eksp. Teor. Phys. 24, 297 (1976)
[Sov. JETP Lett. 24, 266 (1976)].
5. L.A. Alekseeva and I.N. Krupskii, Fiz. Nizk. Temp. 10, 327
(1984) [Sov. J. Low Temp. Phys. 10, 170 (1984)].
6. A.N. Aleksandrovskii, E.A. Kir’yanova, V.G. Manzhelii,
A.V. Soldatov, and A.M. Tolkachev, Fiz. Nizk. Temp. 13,
1095 (1987) [Sov. J. Low Temp. Phys. 13, 623 (1987)].
7. Q. Xiong and H.J. Maris, J. Low Temp. Phys. 81, 167
(1990).
8. L.A. Alekseeva, E.S. Syrkin, and L.A. Vashchenko, Fiz.
Tverd. Tela (St. Peterburg) 45, 1024 (2003) [Sov. Phys.
Solid State 45, 1073 (2003)].
9. L.A. Alekseeva, V.D. Natsik, B.A. Halin, and A.V.
Pustovalova, Fiz. Nizk. Temp. 14, 1127 (1988) [Sov. J. Low
Temp. Phys. 14, 621 (1988)].
10. K.A. Chishko, Fiz. Nizk. Temp. 15, 106 (1989) [Sov. J.
Low Temp. Phys. 15, 61 (1989)].
11. I.N. Krupskii, A.V. Leont’eva, L.A. Indan, and O.V.
Evdokimova, Fiz. Nizk. Temp. 3, 933 (1977) [Sov. J. Low
Temp. Phys. 3, 453 (1977)].
12. V.M Andreev, Yu.A. Zel’vinskii, and S.G. Katal’nikov,
Heavy Hydrogen Isotopes in Nuclear Engeneering,
Energoatomizdat, Moscow (1987) [in Russian].
13. V.S. Boiko, R.I. Garber, and A.M. Kosevich, Reversible
Plasticity of Crystalls, Nauka, Moscow (1991) [in Russian].
14. J. Friedel, Dislocations, Pergamon, Oxford (1964); Mir,
Moscow (1967).
15. S.E. Kal’noi and M.A. Strzhemechny, Fiz. Nizk. Temp. 11,
803 (1985) [Sov. J. Low Temp. Phys. 11, 440 (1985)].
16. B.V. Petuhov and V.L. Pokrovskii, Pis’ma Zh. Eksp. Teor.
Phys. 15, 63 (1972) [Sov. JETP Lett. 15, 44 (1972)].
17. M.A. Strzhemechny, Fiz. Nizk. Temp. 10, 663 (1984) [Sov.
J. Low Temp. Phys. 10, 348 (1984)].
Plasticity of parahydrogen with reduced deuterium contents
Fizika Nizkikh Temperatur, 2007, v. 33, Nos. 6/7 675
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