Off-center impurities
Off-centering of impurities is an interesting phenomenon that was discovered
in 1965 in KCl crystals doped with Li. The off-centering manifests in the
displacement of small atoms, which substitute for larger ones, from
regular sites in a lattice. The displacement can be sufficiently large,
typically 0.5-1 A. The reason of instability of off-center impurity is
the inability of the reduced repulsive forces to oppose the action of the
polarization force (attractive interaction between the charged ion and the
polarization induced by it in a lattice). Since the discovery of the
off-centering of lithium in potassium chloride, the off-center behaviour
was found for many other small impurities in different crystals (see the
list of known off-center impurities in crystals).
Investigation of narrow-gap IV-VI semiconductors (mainly lead telluride PbTe
and lead selenide PbSe) doped with off-center impurities (like germanium or
sulfur) attracts much attention due to impurity-induced phase transitions
in these incipient ferroelectrics. The changes in the physical properties
of these semiconductors due to the ferroelectric phase transition may be used
in the infrared optoelectronics (tunable infrared lasers, photoelectric
devices).
Systematic studies which have been carried out in our laboratory discovered a
whole class of off-center impurities in IV-VI semiconductors. New relaxation
and hysteresis phenomena were found in quaternary solid solutions of IV-VI
semiconductors. In addition to the ferroelectric state, two disordered dipolar
states (dipolar glass and quenched dipolar disorder) were realized and studied
in these crystals. Influence of different impurities on the ferroelectric
phase transitions was also investigated. At present we continue to study these
phenomena using EXAFS (X-ray absorption)
spectroscopy and synchrotron radiation.
The recent result of these studies is the discovery of a new class of
off-center ions -- off-center ions of large size.
Members of the group:
Selected publications:
- Kh.A. Abdullin, A.I. Lebedev, A.M. Gas'kov, V.N. Demin and V.P. Zlomanov.
Structural phase transition in the solid
solution PbTeS. Pis'ma v Zh. Teor. Eksp. Fiz. 40, 229 (1984)
(in Russian). [Translation: JETP Lett. 40, 998 (1984)].
- Kh.A. Abdullin, V.N. Demin and A.I. Lebedev. Scattering of free carriers
near a phase transition in the solid solution PbTeS. Fizika Tverdogo Tela
28, 1020 (1986) (in Russian)
[Translation: Sov. Phys. - Solid State
28, 570 (1986)].
- V.F. Kozlovskii, A.I. Lebedev and Yu.E. Petrov. X-ray and electrical
studies of the phase transition in PbGeSe. Fizika Tverdogo Tela 28,
3610 (1986) (in Russian).
[Translation: Sov. Phys. - Solid State 28,
2035 (1986)].
- A.I. Lebedev and I.A. Sluchinskaya. Phase transitions in PbGeTeS solid
solutions caused by noncentral Ge and S ordering.
Bull. Acad. Sci. USSR Phys. ser. 51(10), 17 (1987).
- A.I. Lebedev and I.A. Sluchinskaya. Possible appearance of the
dipole-glass phase in solid solutions of the semiconductors of the group
IV-VI. Pis'ma v Zh. Teor. Eksp. Fiz.
46, 425 (1987) (in Russian) [Translation: JETP Lett. 46, 536
(1987)].
- V.F. Kozlovskii and A.I. Lebedev. X-ray diffraction investigations of
phase transitions in narrow-gap IV-VI semiconductors. Fizika Tverdogo
Tela, 30, 531 (1988) (in Russian).
[Translation: Sov. Phys. - Solid State
30, 303 (1988)].
- A.I. Lebedev and I.A. Sluchinskaya. Structural disorder and phase
transition in PbSnTeSe. Fizika Tverdogo Tela 32, 1780 (1990) (in Russian).
[Translation: Sov. Phys. - Solid State
32, 1036 (1990)].
- A.I. Lebedev and I.A. Sluchinskaya. New arguments in support of the
off-center positions of the tin atoms in PbSnTeSe and PbSnTeS. Fizika
Tverdogo Tela 34, 1491 (1992) (in Russian).
[Translation: Sov. Phys. - Solid State
34, 793 (1992)].
- A.I. Lebedev and I.A. Sluchinskaya.
Influence of dopants on ferroelectric phase transitions in PbTeS and PbGeTe.
Fizika Tverdogo Tela 35, 629 (1993) (in Russian)
[Translation: Physics of the Solid State
35, 321 (1993)].
- A.I. Lebedev and I.A. Sluchinskaya.
Unusual phase transitions in
PbSnTeSe and PbSnTeS crystals induced by Sn off-center ions.
Ferroelectrics 143, 91 (1993).
- A.I. Lebedev and I.A. Sluchinskaya.
Ferroelectric phase transitions
in IV-VI semiconductors associated with off-center ions. Ferroelectrics
157, 275 (1994).
- A.I. Lebedev and I.A. Sluchinskaya.
Low-temperature phase transitions in some
quaternary solid solutions of IV-VI semiconductors.
J. Alloys and Compounds 203, 51 (1994).
- A.I. Lebedev and I.A. Sluchinskaya.
Influence of random fields on the
ferroelectric phase transitions in IV-VI semiconductors.
Ferroelectrics 169, 293 (1995).
- A.I. Lebedev, I.A. Sluchinskaya, V.N. Demin and I.H. Munro. EXAFS studies
of the influence of impurities on the phase transition in GeTe.
Izv. Akad. Nauk, Ser. Fiz. 60,
N 10, 46 (1996) (in Russian).
- A.I. Lebedev, I.A. Sluchinskaya, V.N. Demin and
I.H. Munro. Off-centering of Pb and Sn
impurities in GeTe induced by strong local stress. The 9th Int.
Conf. on X-ray Absorption Fine Structure (Grenoble, August 1996),
Program and Abstracts, Abstract PS3-82.
- A.I. Lebedev, I.A. Sluchinskaya, V.N. Demin and
I.H. Munro. Off-centering of Pb and Sn impurities in GeTe induced by
strong local stress. Pis'ma v Zh. Eksp.
Teor. Fiz. 63, 600 (1996) (in Russian) [Translation:
JETP Letters 63, 635 (1996)].
- A.I. Lebedev, I.A. Sluchinskaya, V.N. Demin and I.H. Munro.
Off-centering of Pb and Sn impurities in
GeTe. Phys. Rev. B 55, 14770 (1997).
- A.I. Lebedev, I.A. Sluchinskaya, V.N. Demin and I.H. Munro.
Influence of Se, Pb and Mn impurities on the
ferroelectric phase transition in GeTe studied by EXAFS.
Phase Transitions 60, 67 (1997).
- A. Lebedev, I. Sluchinskaya, I. Munro.
EXAFS study of PbS-SnS solid solution.
J. Synchr. Rad. 8, 800 (2001).
- A.I. Lebedev, I.A. Sluchinskaya. Direct
determination of the shape of potential well for off-center Ge atom in
GeTe-SnTe solid solution by EXAFS technique.
7th Russia/CIS/Baltic/Japan Symposium on Ferroelectricity
(St. Petersburg, June 2002). Abstract book, p. 29.
- A.I. Lebedev, I.A. Sluchinskaya. Parameters of the potential well of
an off-center Ge atom in GeTe-SnTe solid solution. Fizika Tverdogo Tela
49, 1077 (2007) (in Russian).
[Translation: Physics of
the Solid State 49, 1132 (2007).]
- A.I. Lebedev, I.A. Sluchinskaya, A. Erko, A.A. Veligzhanin, A.A. Chernyshov.
XAFS studies of the local
environment of Pb impurity atoms in barium, strontium, and calcium
titanates. Physics of the Solid State 51, 991 (2009).
- A.I. Lebedev, I.A. Sluchinskaya, A. Erko, V.F. Kozlovskii.
Direct evidence for off-centering
of Mn impurity in SrTiO3. JETP Letters 89, 457 (2009).
- I.A. Sluchinskaya, A.I. Lebedev, A. Erko. Local environment and oxidation
state of Mn impurity in SrTiO3 determined from XAFS data. --
Bull. Russian Acad.
Sci.: Physics 74, 1235 (2010);
[local copy].
- I.A. Sluchinskaya, A.I. Lebedev. Cobalt in strontium titanate as a new off-center magnetic impurity. --
Physics of the Solid State 61, 390 (2019);
e-print arXiv:2108.00481 (2021).
- I.A. Sluchinskaya, A.I. Lebedev. On the possibility of incorporation of the iron impurity into A sites in SrTiO3. --
Physics of the Solid State 64, 345 (2022);
e-print arXiv:2204.12775 (2022).
Russian version of this page
Physics of Semiconductors division