The diffusion of molecules adsorbed in a one-dimensional channel with side pockets is investigate... more The diffusion of molecules adsorbed in a one-dimensional channel with side pockets is investigated in the framework of a one-dimensional lattice-gas model. The model can describe the molecules migration in some type of zeolites. We obtained the exact expression for the free energy of this model. Using the local equilibrium approximation we derived the analytical expressions for the diffusion coefficients. The concentration dependencies of the center-of-mass and Fickian diffusion coefficients are calculated for some representative values of the lateral interactions between molecules. The theoretical dependencies are compared with the numerical data obtained by the kinetic Monte Carlo simulations. The data obtained by the two completely different methods coincide amazingly well in the whole concentration and wide interaction regions.
Recently, a lot of magneto-optical (MO) thin film media composed from an active MO film and some ... more Recently, a lot of magneto-optical (MO) thin film media composed from an active MO film and some other dielectric and metallic films, used for optimization of MO response, were suggested. Practical realization of such complicated systems also requires the possibility of ex- post characterization of the prepared sample in the sense of determination of exact film thicknesses and/or optical constants.
Size-controlled Cu clusters are formed in a system which combines pulsed magnetron sputtering and... more Size-controlled Cu clusters are formed in a system which combines pulsed magnetron sputtering and gas condensation at room temperature. The discharge repetition frequency (0.125kHz) and the duty cycles (2090%) of the magnetron sputtering are varied ...
ABSTRACT The polarized absorption spectra of nonstoichiometric LiNbO3: Er3+, Mg crystals were inv... more ABSTRACT The polarized absorption spectra of nonstoichiometric LiNbO3: Er3+, Mg crystals were investigated in the region of 4I15/2 --> 2H11/2 transition at 77K. As it follows from the comparison with earlier obtained spectra of LiNbO3: Er3+, the Mg-codoping produces additional lines most probably caused by the appearance of new impurity centers. Using a sensitive differential technique, the effect of the external electric field on the absorption spectra of LiNbO3: Er3+, Mg crystals was studied. The linear Stark effect was observed. The properties of Stark effect show the trigonal C3-symmetry of local centers, which are responsible for the additional lines.
ABSTRACT The optical functions of strontium titanate (SrTiO3) (STO) single crystals were determin... more ABSTRACT The optical functions of strontium titanate (SrTiO3) (STO) single crystals were determined with spectroscopic ellipsometry in the 1–6 eV spectral region and the 4.2–300 K temperature region. On approaching the band gap edge, the optical absorption shows Urbach tail behavior followed by the onset of indirect optical transitions starting at ~3.2 eV and extending up to ~3.68 eV; then direct transitions are very well seen. The refractive index and its temperature and spectral dependences were obtained. In the visible region, the refractive index rises on cooling (negative thermooptic effect) down to 50 K, saturating at lower temperatures. The energy of indirect interband optical transitions increases on cooling up to 3.23 eV at 100 K. The observed magnitude ∂E/∂T=−1.7×10−4 eV K−1 is typical of ionic crystals. Surprisingly, the absorption edge in the region of the lowest direct interband optical transitions 3.7–4 eV shifts to lower energies on cooling. It is concluded that the presence of this 'soft electronic band' together with the rise in absorption intensity at 4.8 eV is responsible for the increase of refractive index on cooling, elucidating the origin of the negative proper thermooptics in STO.
We report the results of an electron spin resonance study of Ti3+ centres in SrTiO3 single crysta... more We report the results of an electron spin resonance study of Ti3+ centres in SrTiO3 single crystals. The Ti3+ centres are created in perturbed regular Ti4+ sites by trapping a photoelectron from the conduction band after ultraviolet irradiation of the sample at low temperature (T < 180 K). The centres are stable below ~180 K. To our knowledge this is the first observation of such Ti3+ defects in a SrTiO3 lattice. At T > Tc (Tc approx 105 K corresponds to the temperature of the cubic-tetragonal phase transition), the Ti3+ centre exhibits an orthorhombic symmetry of the g-tensor with its principal axes oriented exactly along langle001rangle and langle110rangle crystal directions: g[110] = 1.9920, g[1bar 10] = 1.9375, g[001] = 1.8843. At T < Tc, due to a structural phase transition, two of the Ti3+ principal axes are tilted relative to the langle110rangle directions by up to +/-8circ in the (001) crystal plane. The spectroscopic data are explained assuming Jahn-Teller orthorhombic distortions of the oxygen octahedron with non-linear T2g × (eg + t2g) vibronic coupling.
Electron paramagnetic resonance (EPR) of Mn2+ and Fe3+ ions has been used as a probe of local sta... more Electron paramagnetic resonance (EPR) of Mn2+ and Fe3+ ions has been used as a probe of local static and dynamic lattice distortions in the relaxor ferroelectric PbMg1/3Nb2/3O3 (PMN) and solid solutions (1-x)PbMg1/3Nb2/3O3 – xPbTiO3 (x = 0.075–0.33) at temperatures from 290 to 800 K. We have found that the spectrum of the both ions in PMN contains two components: One component corresponds to the resonances from the lattice regions where the perovskite cubic structure is distorted statically while the second component corresponds to the regions where ionic displacements undergo significant dynamic fluctuations. The EPR spectrum from these lattice regions shows the motional narrowing behavior at 350–500 K. We assign these regions with reorientable polar nanoregions responsible for the dielectric relaxation in PMN. From the motional narrowing of the spectral lines, we have determined parameters of the Vogel--Fulcher law describing the rate of ionic hopping between symmetrically equivalent off-center position...
Laser absorption spectroscopy of aluminium atoms in pulsed magnetron discharge with pure argon, a... more Laser absorption spectroscopy of aluminium atoms in pulsed magnetron discharge with pure argon, argon/oxygen, and argon/methane gas mixtures is reported. Time-averaged densities and temperatures of sputtered aluminium atoms were extracted from the absorption signal. The measured Al density depended almost linearly on the pulse current and showed a small dependence on pressure. Al atom temperature increased with discharge current and vice versa with pressure. A drastic decrease of the Al atom density was observed in the Ar/O2 mixture. The Al density dropped to a value close to zero once a critical oxygen gas flow rate was reached. This critical oxygen gas flow was significantly higher in pulsed mode than in DC mode.
Résumé/Abstract Recently we reported on an reentrant dipole glass-like phase formation in K 0. 9 ... more Résumé/Abstract Recently we reported on an reentrant dipole glass-like phase formation in K 0. 9 9 8 6 Li 0. 0 0 1 4 Ta 0. 9 7 6 Nb 0. 0 2 4 O 3 (V. Trepakov et al.: Phys. Rev. B 63 (2001) 172203). Here we present the detailed low-frequency dielectric permittivity and ...
The diffusion of molecules adsorbed in a one-dimensional channel with side pockets is investigate... more The diffusion of molecules adsorbed in a one-dimensional channel with side pockets is investigated in the framework of a one-dimensional lattice-gas model. The model can describe the molecules migration in some type of zeolites. We obtained the exact expression for the free energy of this model. Using the local equilibrium approximation we derived the analytical expressions for the diffusion coefficients. The concentration dependencies of the center-of-mass and Fickian diffusion coefficients are calculated for some representative values of the lateral interactions between molecules. The theoretical dependencies are compared with the numerical data obtained by the kinetic Monte Carlo simulations. The data obtained by the two completely different methods coincide amazingly well in the whole concentration and wide interaction regions.
Recently, a lot of magneto-optical (MO) thin film media composed from an active MO film and some ... more Recently, a lot of magneto-optical (MO) thin film media composed from an active MO film and some other dielectric and metallic films, used for optimization of MO response, were suggested. Practical realization of such complicated systems also requires the possibility of ex- post characterization of the prepared sample in the sense of determination of exact film thicknesses and/or optical constants.
Size-controlled Cu clusters are formed in a system which combines pulsed magnetron sputtering and... more Size-controlled Cu clusters are formed in a system which combines pulsed magnetron sputtering and gas condensation at room temperature. The discharge repetition frequency (0.125kHz) and the duty cycles (2090%) of the magnetron sputtering are varied ...
ABSTRACT The polarized absorption spectra of nonstoichiometric LiNbO3: Er3+, Mg crystals were inv... more ABSTRACT The polarized absorption spectra of nonstoichiometric LiNbO3: Er3+, Mg crystals were investigated in the region of 4I15/2 --&gt; 2H11/2 transition at 77K. As it follows from the comparison with earlier obtained spectra of LiNbO3: Er3+, the Mg-codoping produces additional lines most probably caused by the appearance of new impurity centers. Using a sensitive differential technique, the effect of the external electric field on the absorption spectra of LiNbO3: Er3+, Mg crystals was studied. The linear Stark effect was observed. The properties of Stark effect show the trigonal C3-symmetry of local centers, which are responsible for the additional lines.
ABSTRACT The optical functions of strontium titanate (SrTiO3) (STO) single crystals were determin... more ABSTRACT The optical functions of strontium titanate (SrTiO3) (STO) single crystals were determined with spectroscopic ellipsometry in the 1–6 eV spectral region and the 4.2–300 K temperature region. On approaching the band gap edge, the optical absorption shows Urbach tail behavior followed by the onset of indirect optical transitions starting at ~3.2 eV and extending up to ~3.68 eV; then direct transitions are very well seen. The refractive index and its temperature and spectral dependences were obtained. In the visible region, the refractive index rises on cooling (negative thermooptic effect) down to 50 K, saturating at lower temperatures. The energy of indirect interband optical transitions increases on cooling up to 3.23 eV at 100 K. The observed magnitude ∂E/∂T=−1.7×10−4 eV K−1 is typical of ionic crystals. Surprisingly, the absorption edge in the region of the lowest direct interband optical transitions 3.7–4 eV shifts to lower energies on cooling. It is concluded that the presence of this &#39;soft electronic band&#39; together with the rise in absorption intensity at 4.8 eV is responsible for the increase of refractive index on cooling, elucidating the origin of the negative proper thermooptics in STO.
We report the results of an electron spin resonance study of Ti3+ centres in SrTiO3 single crysta... more We report the results of an electron spin resonance study of Ti3+ centres in SrTiO3 single crystals. The Ti3+ centres are created in perturbed regular Ti4+ sites by trapping a photoelectron from the conduction band after ultraviolet irradiation of the sample at low temperature (T < 180 K). The centres are stable below ~180 K. To our knowledge this is the first observation of such Ti3+ defects in a SrTiO3 lattice. At T > Tc (Tc approx 105 K corresponds to the temperature of the cubic-tetragonal phase transition), the Ti3+ centre exhibits an orthorhombic symmetry of the g-tensor with its principal axes oriented exactly along langle001rangle and langle110rangle crystal directions: g[110] = 1.9920, g[1bar 10] = 1.9375, g[001] = 1.8843. At T < Tc, due to a structural phase transition, two of the Ti3+ principal axes are tilted relative to the langle110rangle directions by up to +/-8circ in the (001) crystal plane. The spectroscopic data are explained assuming Jahn-Teller orthorhombic distortions of the oxygen octahedron with non-linear T2g × (eg + t2g) vibronic coupling.
Electron paramagnetic resonance (EPR) of Mn2+ and Fe3+ ions has been used as a probe of local sta... more Electron paramagnetic resonance (EPR) of Mn2+ and Fe3+ ions has been used as a probe of local static and dynamic lattice distortions in the relaxor ferroelectric PbMg1/3Nb2/3O3 (PMN) and solid solutions (1-x)PbMg1/3Nb2/3O3 – xPbTiO3 (x = 0.075–0.33) at temperatures from 290 to 800 K. We have found that the spectrum of the both ions in PMN contains two components: One component corresponds to the resonances from the lattice regions where the perovskite cubic structure is distorted statically while the second component corresponds to the regions where ionic displacements undergo significant dynamic fluctuations. The EPR spectrum from these lattice regions shows the motional narrowing behavior at 350–500 K. We assign these regions with reorientable polar nanoregions responsible for the dielectric relaxation in PMN. From the motional narrowing of the spectral lines, we have determined parameters of the Vogel--Fulcher law describing the rate of ionic hopping between symmetrically equivalent off-center position...
Laser absorption spectroscopy of aluminium atoms in pulsed magnetron discharge with pure argon, a... more Laser absorption spectroscopy of aluminium atoms in pulsed magnetron discharge with pure argon, argon/oxygen, and argon/methane gas mixtures is reported. Time-averaged densities and temperatures of sputtered aluminium atoms were extracted from the absorption signal. The measured Al density depended almost linearly on the pulse current and showed a small dependence on pressure. Al atom temperature increased with discharge current and vice versa with pressure. A drastic decrease of the Al atom density was observed in the Ar/O2 mixture. The Al density dropped to a value close to zero once a critical oxygen gas flow rate was reached. This critical oxygen gas flow was significantly higher in pulsed mode than in DC mode.
Résumé/Abstract Recently we reported on an reentrant dipole glass-like phase formation in K 0. 9 ... more Résumé/Abstract Recently we reported on an reentrant dipole glass-like phase formation in K 0. 9 9 8 6 Li 0. 0 0 1 4 Ta 0. 9 7 6 Nb 0. 0 2 4 O 3 (V. Trepakov et al.: Phys. Rev. B 63 (2001) 172203). Here we present the detailed low-frequency dielectric permittivity and ...
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