Viktor Bursian. Publications

Viktor E. Bursian

S.A.Basun, V.E.Bursian, A.G.Razdobarin, L.S.Sochava.
Anisotropic Photoionization as a Mechanism of Axial Iron Center Alignment in KTaO₃.
Physics of the Solid State 43 (6), (2001).: An EPR study has revealed photoinduced recharging and optical alignment of the Fe⁴⁺_Ta--V_O tetragonal complexes in KTaO₃. The data on the optical creation and destruction of this center by light of different polarizations and wavelengths are discussed together with similar results obtained for the Fe³⁺_K--O_i center. These two centers were established to undergo mutual charge transfer, in which the electron released in the photoionization of the Fe²⁺_K--O_i center is trapped by the Fe⁵⁺_Ta--V_O center. Irradiation by light with photon energy below 2.05 eV, which is the ionization threshold of Fe²⁺_K--O_i, reverses this process. In both cases, the absorption cross section depends on the orientation of the center axis relative to the light polarization vector. As a result, the Fe⁴⁺_Ta--V_O and Fe³⁺_K--O_i tetragonal centers acted upon by polarized light undergo orientation-sensitive photorecharging, and the defects with the given charge state are no longer characterized by an equally probable axial distribution over the three <100> directions. This mechanism, which does not involve real reorientations of the Fe_Ta--V_O and Fe_K--O_i complexes, gives rise, nevertheless, to the alignment of the centers along (at right angles to) the light polarization vector.

L.S.Sochava, V.E.Bursian, A.G.Razdobarin.
Electric-field-induced orientation of iron tetragonal centers in KTaO₃.
Physics of the Solid State 42 (9), 1640-1642 (2000).: Fe³⁺_K--O_i^2- impurity centers in a KTaO₃ sample to which a dc electric field E = 75 kV/cm is applied are shown to be oriented at temperatures T greater than or equal to 120 K. In these conditions, the effective local field acting on the electric dipole moment of a center exceeds the applied field by a factor 7.6.

H.Riesen, V.E.Bursian, N.B.Manson.
Efficient non-photochemical spectral hole burning in single-crystal SrO : Co²⁺.
Journal of Luminescence 85 (1-3), 107-112 (1999).: Efficient non-photochemical spectral hole burning is observed in the zero phonon line at 740 nm of Co²⁺ doped in single-crystal SrO. The Co²⁺ ions substitute for Sr²⁺ ions and occupy [111] off-centre positions in SrO. Due to strain and a distribution of internal electric fields in the host crystal the eight equivalent sites can have different energies and different transition frequencies. The hole burning is attributed to light-induced rearrangements between these eight sites. Such a process can be described in terms of the two-level systems model normally used for photophysical hole burning of glasses. The efficiency of the hole burning process is determined to be approximate to 0.07. Also, the luminescence spectrum of the lowest excited state at 1300 nm is reported.

D.V.Azamat, S.A.Basun, V.E.Bursian, A.G.Razdobarin, L.S.Sochava, H.Hesse, S.Kapphan.
EPR of a non-Kramers iron ion in KTaO₃.
Physics of the Solid State 41 (8), 1303-1306 (1999).: The EPR spectrum of the non-Kramers iron ion Fe⁴⁺ (S = 2) in a KTaO₃:Fe crystal appearing after illumination of the sample in the visible has been detected and studied. Because of the large initial splitting (\D\ = 4.15 cm(-1)), only transitions within the \+/- 1 > and \+/- 2 > doublets are seen experimentally. Superhyperfine structure in the spectrum of a non-Kramers ion in perovskites has been detected for the first time. A structure is proposed for the center responsible for the new EPR spectrum, which represents a complex of a Fe⁴⁺ ion substituting for Ta with an oxygen vacancy at the nearest anion site.

V.E.Bursian, V.S.Vikhnin, L.S.Sochava, S.Kapphan, H.Hesse.
Observation of superhyperfine structure in the ESR spectra of two tetragonal Fe centers in KTaO₃ and a new model for the center.
Physics of the Solid State 39 (4), 547-549 (1997).: Superhyperfine structure is observed in the lines of the ESR spectra of two tetragonal iron centers in the KTaO₃ crystal, namely, ''Fe 4/2'' and Fe³⁺_Ta--V_O. Analysis of the superhyperfine structure of the former of these centers shows that the iron ion replaces Ta5+ and is found in the charge state 5+. Justification is given for assuming that the tetragonal symmetry of the center is due to the displacement of Fe⁵⁺ from the Ta⁵⁺ site along a [100] direction to an off-center position.

S.A.Basun, V.E.Bursian, H.Hesse, S.Kapphan, L.S.Sochava, V.S.Vikhnin.
Polarization sensitive photo recharging and optical alignment of the tetragonal Fe³⁺ centers in KTaO₃.
Proc. of the 13th Internat. Conf. on
Defects in Insulating Materials (ICDIM 96),
Materials Science Forum 239-241, 345-348 (1997).: Orientation sensitive recharging of tetragonal Fe_K--O_i centers in KTaO₃ under polarized optical irradiation was observed resulting in the ''alignment'' of the centers in particular charge state. The sign of the alignment altered in the course of irradiation. A phenomenological model involving photo charge transport allowed for a semiquantitative description of the experiments.

S.A.Basun, V.E.Bursian, V.S.Vikhnin, A.A.Kaplyansky, P.A.Markovin, L.S.Sochava, U.Bianchi, W.Kleemann.
Photoinduced charge transfer in SrTiO₃.
Izvestija Akad. Nauk, ser.fiz., 60 (10), 20-29 (1996).
In Russian.

S.A.Basun, U.Bianchi, V.E.Bursian, A.A.Kaplyanskii, W.Kleemann, L.S.Sochava, V.S.Vikhnin.
Study of photoinduced charge transfer in SrTiO₃: luminescence, photoconductivity and photo-EPR.
SPIE Proc. 2706, 73-82 (1996).

S.A.Basun, U.Bianchi, V.E.Bursian, A.A.Kaplyanskii, W.Kleemann, L.S.Sochava, V.S.Vikhnin.
Photoinduced Phenomena in Sr_1-xCa_xTiO₃, 0 <= x <= 0.12.
Ferroelectrics 183, 255-264 (1996).

S.A.Basun, U.Bianchi, V.E.Bursian, A.A.Kaplyanskii, W.Kleemann, L.S.Sochava, V.S.Vikhnin.
Charge transfer processes and dynamic equilibrium of electronic state occupancies in optically excited SrTiO₃:Cr crystals.
Journal of Luminescence 66&67 (1-6), 526-530 (1995).: Spectral and kinetic measurements of ²E --> ⁴A₂ photoluminescence (PL) in SrTiO₃ crystals containing small amounts of Cr were performed and a strong effect of IR illumination on the PL was observed. The dominant photoionization mechanism of Cr³⁺ PL excitation was established. The locations in the SrTiO₃ band gap of Cr³⁺ donor levels (1.85 eV below the bottom of the conduction band) and of Cr⁴⁺ acceptor levels (1.4 eV above the top of the valence band) were found. A new mechanism of optical erasing of burnt spectral holes of the R lines in SrTiO₃:Cr was determined.

V.Trepakov, F.Smutny, V.Vikhnin, V.Bursian, L.Sochava, L.Jastrabik, P.Syrnikov.
The effect of local ordering in a system of defects in weakly doped KTaO₃: Dielectric anomalies and their origin.
Radiation Effects and Defects in Solids 134 (1-4), 325-328 (1995).: The temperature-frequency behaviour of the permittivity epsilon'(T, f) and tg delta(T, f) (20-300 K, 120 Hz-9 MHz), EPR, optical absorption and luminescence of KTaO₃ single crystals, pure and with Li 0.1; Cr 0.02; Cu 3; Fe 1; Li 0.1 + Cr 0.1, and Li 0.1 + Cr 0.1 + Cu 0.02 wt.%, were studied. Below 70 K, in all the doped samples, dielectric dispersion occurs, with tg delta(T) maxima obeying Arrhenius law. This is associated with a local ordering in dipole-dipole clusters (which contain reorienting defects of various kind) with correlations due to interactions via the TO-soft mode.

V.Trepakov, F.Smutny, V.Vikhnin, V.Bursian, L.Sochava, L.Jastrabik, P.Syrnikov.
The effects of defect system ordering in a weakly doped incipient ferroelectric (KTaO₃): dielectric manifestation.
Journal of Physics: Condensed Matter 7 (19), 3765-3777 (1995).: The temperature-frequency behaviour of the permittivity epsilon'(T,f) and tan[delta(T,f)] (20-300 K; 120 Hz-9 MHz), EPR, optical absorption and luminescence of KTaO₃, nominally pure and weakly doped (0.1 wt% Li; 0.01 wt% Cu; 1 wt% Fe; 0.1 wt% Li + 0.1 wt% Cr and 0.1 wt% Li+0.1 wt% Cr+0.02 wt% Cu) were studied. Below 70 K, in all doped samples, dielectric dispersion occurs, with tan[delta(T)] maxima positions obeying the universal Arrhenius law with activation energy DELTA = 1000 +/- 50 K. This is associated with local ordering in the dipole-dipole clusters containing reorienting defect pairs of various kinds, with correlations due to interaction via the TO soft mode.

V.E.Bursian, V.S.Vikhnin, L.S.Sochava.
Microwave response in high-T_c superconductors as a method of phase transition in the interacting fluxon system investigation.
Soviet Journal of Low Temperature Physics 17 (9), 557-558 (1991).

V.S.Vikhnin, Ya.S.Izygson, I.N.Kurkin, L.L.Sedov, V.E.Bursian, L.S.Sochava.
Spin-lattice relaxation of noncentral paramagnetic Co²⁺ ions in SrO.
Sov.Phys.Solid State 32 (5), 844-846 (1990).: The temperature dependence of the rate 1/T₁ of spin–lattice relaxation of Co²⁺ ions occupying noncentral positions in the crystal lattice of SrO was investigated. This dependence had a linear part, as well as two exponential regions characterized by energies delta₁=79 ± 5 and delta₂=200 ± 20 cm^–1. Possible mechanisms of spin–lattice relaxation of Co²⁺ ions in SrO were analyzed. The experimentally determined energies could represent the gaps between the ground (J=1/2) and excited (J=3/2, J=5/2) spin–orbit multiplets. An excited vibrational state (delta=149 cm^–1) could also contribute to the exponential process characterized by the energy delta₁ because of the anharmonic Raman scattering by a quasilocal vibration.

V.E.Bursian, A.A.Bush, V.S.Vikhnin, I.V.Gladyshev, and L.S.Sochava.
Low-field microwave absorption in bismuth-based high-T_c superconducting single crystals: threshold vortex-lattice effects.

JETP Lett. 50 (3), 135-139 (1989).

A threshold in the magnetic field has been observed for several characteristic effects in the low-field absorption by high-T_c single crystals. A signal of a new type corresponds to the threshold field in the microwave absorption spectrum. The appearance of the new signal in the low-field absorption and of effects which involve a threshold in the magnetic field is linked with a transition from an individual pinning of vortices to a collective pinning.

V.E.Bursian, A.A.Bush, V.S.Vikhnin, I.V.Gladyshev, L.S.Sochava.
Detection of the structure of low-field microwave absorption and magnetic field thresholds of effects occurring in bismuth-based single crystals of high-temperature superconductors.
Sov.Phys.Solid State 31 (7), 1219-1225 (1989).: Experimental and theoretical investigations were made of a low-field signal representing microwave absorption in Bi₂Sr₂CaCu₂O_y high-temperature superconductor single crystals. A complex temperature-dependent structure of the signal was observed. There was a threshold value of the magnetic field above which there were no memory effects. A narrow (<~0.2 Oe) signal of negative polarity exhibited a strong temperature dependence of the intensity with a maximum. The mechanisms responsible for the signal were investigated, including relaxation due to modulation of the magnetic moment by hopping transitions between superconducting regions in a Josephson medium and a resonance associated with tunnel transitions induced by a microwave field in the Josephson medium.

V.E.Bursian, V.S.Vikhnin, L.S.Sochava.
Spin polarization, induced by spin-dependent tunneling: the effect of the inversion of the populations of the off-center paramagnetic ion states.
Izvestija Akad. Nauk, ser.fiz. 52 (3), 477-481 (1988).
In Russian.

V.E.Bursian, V.S.Vikhnin, L.S.Sochava.
Electric field splitting of ESR lines for reorienting dipole centers. Time effects.
Sov.Phys.Solid State 29 (3), 481-484 (1987).: A time dependence was discovered of the electric field splitting of ESR lines for the off-center Co²⁺ impurity ion in the strontium oxide crystal. It was found that such an effect should exist in the spectrum of a reorientable dipole paramagnetic center under both external and internal (defect) fields. A very simple model is used to calculate the ESR line position and profile for the off-center ion in the electric field; the results of the calculation give a qualitative explanation of the main features of the effect.

Viktor E. Bursian

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