Thermodynamically equilibrium point defects in the low-dimensional systems
The temperature dependencies of the electrical resistance of low-dimensional NbSe₃- and NbSe₂-single crystals were investigated in the range of 300–540 K. Measurements of resistance were produced along the chains for quasi-one-dimensional NbSe₃-single crystal and along the layer for quasi-two-dimens...
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Інститут фізики конденсованих систем НАН України
1999
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| Zitieren: | Thermodynamically equilibrium point defects in the low-dimensional systems / A.A. Mamalui, T.N. Shelest, H.B. Chashka // Condensed Matter Physics. — 1999. — Т. 2, № 4(20). — С. 617-620. — Бібліогр.: 5 назв. — англ. |
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irk-123456789-1205862017-06-13T03:05:28Z Thermodynamically equilibrium point defects in the low-dimensional systems Mamalui, A.A. Shelest, T.N. Chashka, H.B. The temperature dependencies of the electrical resistance of low-dimensional NbSe₃- and NbSe₂-single crystals were investigated in the range of 300–540 K. Measurements of resistance were produced along the chains for quasi-one-dimensional NbSe₃-single crystal and along the layer for quasi-two-dimensional NbSe₂-single crystal. On the temperature dependencies the exponential deviations from linear dependencies were observed. We suppose that such deviations of resistance are connected with the contribution of selenium equilibrium vacancies. Досліджено температурні залежності електричного опору низькорозмірних монокристалів NbSe₃ та NbSe₂ в температурному діапазоні 300–540 К. Вимірювання опору виконувалися вздовж ланцюжків для квазіодномірних монокристалів NbSe₃ та вздовж шарів для квазідвомірних монокристалів NbSe₂. На температурних залежностях опору виявлені експоненційні відхилення від лінійної залежності. Припускається, що ці відхилення пов’язані з внесками від рівноважних вакансій селену. 1999 Article Thermodynamically equilibrium point defects in the low-dimensional systems / A.A. Mamalui, T.N. Shelest, H.B. Chashka // Condensed Matter Physics. — 1999. — Т. 2, № 4(20). — С. 617-620. — Бібліогр.: 5 назв. — англ. 1607-324X DOI:10.5488/CMP.2.4.617 PACS: 71.45, 72.15.N, 71.30 http://dspace.nbuv.gov.ua/handle/123456789/120586 en Condensed Matter Physics Інститут фізики конденсованих систем НАН України |
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The temperature dependencies of the electrical resistance of low-dimensional NbSe₃- and NbSe₂-single crystals were investigated in the range of 300–540 K. Measurements of resistance were produced along the chains for quasi-one-dimensional NbSe₃-single crystal and along the layer for quasi-two-dimensional NbSe₂-single crystal. On the temperature dependencies the exponential deviations from linear dependencies were observed. We suppose that such deviations of resistance are connected with the contribution of selenium equilibrium vacancies. |
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Article |
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Mamalui, A.A. Shelest, T.N. Chashka, H.B. |
| spellingShingle |
Mamalui, A.A. Shelest, T.N. Chashka, H.B. Thermodynamically equilibrium point defects in the low-dimensional systems Condensed Matter Physics |
| author_facet |
Mamalui, A.A. Shelest, T.N. Chashka, H.B. |
| author_sort |
Mamalui, A.A. |
| title |
Thermodynamically equilibrium point defects in the low-dimensional systems |
| title_short |
Thermodynamically equilibrium point defects in the low-dimensional systems |
| title_full |
Thermodynamically equilibrium point defects in the low-dimensional systems |
| title_fullStr |
Thermodynamically equilibrium point defects in the low-dimensional systems |
| title_full_unstemmed |
Thermodynamically equilibrium point defects in the low-dimensional systems |
| title_sort |
thermodynamically equilibrium point defects in the low-dimensional systems |
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Інститут фізики конденсованих систем НАН України |
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1999 |
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http://dspace.nbuv.gov.ua/handle/123456789/120586 |
| citation_txt |
Thermodynamically equilibrium point defects in the low-dimensional systems / A.A. Mamalui, T.N. Shelest, H.B. Chashka // Condensed Matter Physics. — 1999. — Т. 2, № 4(20). — С. 617-620. — Бібліогр.: 5 назв. — англ. |
| series |
Condensed Matter Physics |
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AT mamaluiaa thermodynamicallyequilibriumpointdefectsinthelowdimensionalsystems AT shelesttn thermodynamicallyequilibriumpointdefectsinthelowdimensionalsystems AT chashkahb thermodynamicallyequilibriumpointdefectsinthelowdimensionalsystems |
| first_indexed |
2025-07-08T18:10:47Z |
| last_indexed |
2025-07-08T18:10:47Z |
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1837103315024871424 |
| fulltext |
Condensed Matter Physics, 1999, Vol. 2, No. 4(20), pp. 617–620
Thermodynamically equilibrium point
defects in the low-dimensional systems
A.A.Mamalui, T.N.Shelest, H.B.Chashka
Kharkiv State Polytechnic University,
21 Frunze Str., 310002 Kharkiv, Ukraine
Received September 21, 1998
The temperature dependencies of the electrical resistance of low-dimen-
sional NbSe3- and NbSe2-single crystals were investigated in the range of
300–540 K. Measurements of resistance were produced along the chains
for quasi-one-dimensional NbSe3-single crystal and along the layer for
quasi-two-dimensional NbSe2-single crystal. On the temperature depen-
dencies the exponential deviations from linear dependencies were ob-
served. We suppose that such deviations of resistance are connected with
the contribution of selenium equilibrium vacancies.
Key words: low-dimensional systems, electroresistance, vacancies
PACS: 71.45, 72.15.N, 71.30
Numerous experimental and theoretical works [1,2] are devoted to a research
of properties of low-dimensional conducting systems. Due to a reduced dimension-
ality, such compounds have got an anisotropy of physical properties, in particular
anisotropy of conductivity (ρ⊥/ρ//=10–20 at NbSe3 [3]; ρ⊥/ρ//=30–50 at NbSe2 [2])
and at the same time the role of thermodynamic fluctuations increase. It is known
that conductivity hardly depends on concentration of defects. Magnitude of con-
centration of the defects is determined by the significance of the bond energy and
by co-ordination of atoms in the crystal lattice. The NbSe3 and NbSe2 researched
in the present work are typical representatives of quasi-one-dimensional and quasi-
two-dimensional compounds. The compounds of NbSe3 and NbSe2 consist of iden-
tical atoms but they differ by space co-ordination of atoms. For this reason these
compounds were selected as the objects of a comparative experimental research of
vacancy formation processes. The present work is devoted to experimental study
of temperature dependence of a resistance as well as the processes of formation of
thermodynamically equilibrium dot defects (monovacancies) in NbSe 2 and NbSe3.
Crystals of NbSe3 and NbSe2 were prepared using gas transport reaction [4].
Quasi-one-dimensional single crystals NbSe3 [1] consist of a chain formed by trigonal
prisms from Se atoms (figure 1a). At the centre of such prisms the Nb atom is located.
The bond between the chain is weak. It leads to a quasi-one-dimensionality of this
c© A.A.Mamalui, T.N.Shelest, H.B.Chashka 617
A.A.Mamalui, T.N.Shelest, H.B.Chashka
Figure 1. Structures of single crystals of quasi-one-dimensional NbSe3 (a) and
quasi-two-dimensional NbSe2 (b).
compound. The number of the nearest bonds for atom Se (disregarding the bonds
between chains) is equal to six (4 of them are Se-Se bonds, 2 are Nb-Se bonds). The
atom of Nb has 6 nearest Nb-Se bonds and 2 Nb-Nb bonds.
Quasi-two-dimensional single crystals NbSe2 [2] consist of layers, each of which
represents a sandwich from two layers of atoms Se with a layer Nb between them
(figure 1a). The layers NbSe2 interact among themselves in the crystal by weak Van-
der-Vaals forces. Coordination number for Se is 9 (6 bonds of Se-Se and 3 bonds of
Nb-Se). At the atom Nb there are 6 Nb-Se bonds and 6 Nb-Nb bonds. As the number
of bonds for atoms Se, both at NbSe2, and at NbSe3, is less than for Nb, the energy
of vacancy formation of atoms Se is less than the energy of vacancy formation of
atoms Nb. The ratio of the number of the nearest bonds for atoms Se in compounds
NbSe2 and NbSe3 is 9:6. Thus, it is possible to assume that the energy of vacancy
formation of atoms Se in NbSe2 should be approximately 1.5 times higher than at
NbSe3, the energy of vacancy formation of atoms Nb being approximately equal.
The temperature dependencies of the electroresistance of single crystals in low-
dimensional systems NbSe3 and NbSe2 were investigated in the region of tempera-
tures higher than 300 K. The electroresistance was measured using a four-contact
DC circuit along the chains for a quasi-one-dimensional NbSe3-single crystal and
along the layer for a quasi-two-dimensional NbSe2-single crystal. The transport cur-
rent value was such that the electric field at the sample was lower than the threshold
electric field of charge density wave sliding [1].
The temperature dependence of electroresistance of samples NbSe3 and NbSe2 in
618
Defects in the low-dimensional systems
Figure 2. Temperature dependence of electroresistance NbSe3 (a) and activation
energy (b).
the temperature interval of 300–540 K is presented in figures 2a and 3a accordingly.
The obtained temperature dependencies of electroresistance for both single crys-
tals NbSe2, and for NbSe3 show the deviations from the linear dependence at T>To.
In case of well-investigated three-dimensional metals [5], the similar deviations from
the linearity are stimulated by forming thermodynamically equilibrium vacancies.
In our case of low-dimensional systems, the observable effects are also stimulated by
forming thermodynamically equilibrium vacancies. The definition of magnitudes of
activation energies is represented in figures 2b and 3b in coordinates ln(∆R/R) =
f(1/T ) (∆R – residual between experimental and exponential value of resistance
at the temperature T). For NbSe3 the magnitude of energy of activation Ev
f has
made up 0.8 eV (the same result is obtained in the experiment made in vacuum),
for NbSe2 Ev
f=1.2 eV.
Taking into account the results obtained (Ev
f(NbSe2)≈(1,5Ev
f (NbSe3)) we con-
sider the vacancies in NbSe2 and NbSe3 -single crystals to be the vacancies of Se.
However in low-dimensional systems the formation vacancy may lead to breaking
the lattice stability. It is a possible reason of nonrepeatability of experimental results
on different samples.
Figure 3. Temperature dependence of electroresistance NbSe2 (a) and activation
energy (b).
619
A.A.Mamalui, T.N.Shelest, H.B.Chashka
References
1. Electronic Properties of Inorganic Quasi-One-Dimensional Compounds. Monceau P.
(ed.), Dordereht, Boston, Lancaster, D. Reidel Publishing Company, vol. 2, 1985.
2. Wilson J., Joffe A. The transition metal dichalcohenides. // Adv. Phys., 1967, vol. 18,
No. 1, p. 193–337.
3. Ong N.P., Brill J.W. Conductivity anisotropy and transverse magnetoresistance of
NbSe3. // Phys. Rev. B, 1978, vol. 18, No. 10, p. 5265–5271.
4. Chashka Kh.B., Beletskii V.J., Obolenskii M.A. Electrical resistance of NbSe3 single
crystals under uniaxial pressure.// Physica B, 1994, vol. 203, No. 1, p. 75–80.
5. Damask A.C. Point Defects in Metals. New-York, London, 1963.
Термодинамічно рівноважні точкові дефекти в
низькорозмірних системах
А.О.Мамалуй, Т.М.Шелест, Х.Б.Чашка
Харківський державний політехнічний університет,
310002 Харків, вул. Фрунзе, 21
Отримано 21 вересня 1998 р.
Досліджено температурні залежності електричного опору низько-
розмірних монокристалів NbSe3 та NbSe2 в температурному діапа-
зоні 300–540 К. Вимірювання опору виконувалися вздовж ланцюж-
ків для квазіодномірних монокристалів NbSe3 та вздовж шарів для
квазідвомірних монокристалів NbSe2. На температурних залежно-
стях опору виявлені експоненційні відхилення від лінійної залежності.
Припускається, що ці відхилення пов’язані з внесками від рівноваж-
них вакансій селену.
Ключові слова: низькорозмірні системи, опір, вакансії
PACS: 71.45, 72.15.N, 71.30
620
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