Yu. S. Ponosov - Academia.edu (original) (raw)
Papers by Yu. S. Ponosov
The self-consistent linear method of augmented plane waves is used to calculate the energy band s... more The self-consistent linear method of augmented plane waves is used to calculate the energy band structure and the density of states N(E) of hexagonal technetium. A matrix element of the dipole transitions is used to calculate the frequency dependence of the interband optical conductivity U(W) and of the real part E, (a) of the complex permittivity for two directions of polarization of an optical wave relative to the hexagonal c axis of the crystal (Elc and Ellc). The anisotropy of the optical absorption is considered in the photon energy range %J = 0-25 eV. An experimental investigation is reported of the optical properties of a Tc film with the (0001 ) orientation at photon energies E = 0.62-10 eV. A strong absorption band is attributed to the (d-d,p) electron transitions. It is shown that there is a satisfactory agreement between the experimentally observed and calculated functions a, (o) and E: (w)
High Pressure Research
Pressure-induced phase transitions of lead chalcogenides were studied by Raman spectroscopy. The ... more Pressure-induced phase transitions of lead chalcogenides were studied by Raman spectroscopy. The number of Raman modes observed for the first high-pressure phases was found to be significantly less than expected from selection rules for the proposed GeS-type orthorhombic structure. The observations are consistent with the alternative assignment as CrB-type. In the case of PbS, the disappearance of the intermediate-phase Raman lines in the pressure range of 19–25 GPa, i.e., in the vicinity of the orthorhombic to CsCl-type phase transition, is accompanied by a strong increase in a structureless background. The Raman background is attributed to light scattering by charge carriers in the metallic CsCl-type phase.
Bulletin of the Russian Academy of Sciences: Physics, 2010
Silica films implanted with selenium ions (330 keV, 5 × 10 16 cm -2 ) were studied. The method of... more Silica films implanted with selenium ions (330 keV, 5 × 10 16 cm -2 ) were studied. The method of optically stimulated electron emission (OSEE) was used to analyze features specific to disordering of the film structure. Spectrum dependences of the OSEE are described in terms of the formalism of Urbach's emission rule. It was found that the discrete continuum disturbances arising upon implantation considerably distort the spectrum of the electronic and vibrational states of the SiO 2 matrix. Results of the experiment and the numerical simulation provide evidence for the activation tunneling of electrons from optically excited surface states of SiO 2 to a vacuum.
Physics of the Solid State, 2014
ABSTRACT The interaction of YBa2Cu3O6.8 (123) with water vapors at T = 200°C and the water influe... more ABSTRACT The interaction of YBa2Cu3O6.8 (123) with water vapors at T = 200°C and the water influence on the structure and electrophysical properties of the compound have been studied using Raman spectroscopy, magnetometry, and X-ray diffraction. It has been found that the penetration of water into the 123 structure leads to its transition to a hydride-oxyhydroxide H2x − z YBa2Cu3O y + x − z (OH) z containing fragments of the 124-type structure and exhibiting the spectrum of two-magnon scattering characteristic of antiferromagnetic 123 á compositions; in this case, the superconducting properties of the material as a whole are conserved. After short-time recovery annealing and subsequent oxidation, the water is removed from the compound structure, which leads to the disappearance of the spectrum of spin fluctuations. A possible mechanism of change in the 123 structure upon hydrogen and water intercalation has been discussed.
Trends in Magnetism, 2011
Features of the optical properties of nanostructured strongly correlated oxides CuO, Y 3 Fe 5 O 1... more Features of the optical properties of nanostructured strongly correlated oxides CuO, Y 3 Fe 5 O 12 , and FeBO 3 in a wide range of energies, which includes both the fundamental absorption region, low-energy electron excitations, and phonon modes have been investigated by methods of optical spectroscopy. Absorption and reflection spectra, Raman spectra, and ellipsometry measurements are carried out on the samples of oxide nanostructured ceramics. High-density nanoceramics were prepared by shock-wave loading and high pressure torsion methods from coarse-grain oxide powders. Strong smearing of the fundamental absorption edge is revealed for all nanoceramics. Anomalous red shift of the absorption edge E g is found in CuO nanooxide. The features of the optical functions in nanooxides of 3d-metals may be attributed to high defectiveness of nanooxides, peculiarities in the electronic structure of strongly correlated oxides and their tendency to electronic phase separation.
Inorganic Materials, 2006
The crystal structure of the low-temperature form of K 3 PO 4 has been determined for the first t... more The crystal structure of the low-temperature form of K 3 PO 4 has been determined for the first time using neutron diffraction (Rietveld method) and Raman spectroscopy: orthorhombic cell (sp. gr. Pnma , Z = 4), lattice parameters a = 1.12377(2) nm, b = 0.81046(1) nm, c = 0.59227(1) nm. The structure is made up of isolated [PO 4 ] tetrahedra, with the potassium ions in between.
Physics of the Solid State, 2001
The temperature dependences (5-300 K) of the Raman spectra of E 2 g phonons and optical constants... more The temperature dependences (5-300 K) of the Raman spectra of E 2 g phonons and optical constants in zinc single crystals are measured in the excitation energy range 1.4-2.54 eV. It is found that phonon damping decreases upon an increase in the wavelength of exciting radiation. The obtained results are compared with the dependence of the phonon width on the excitation energy (the probed wave vector of the excitations under investigation), which are presented for the first time for the transition metal osmium, as well as with the calculated electron-phonon renormalization of damping, taking into account the actual distribution of wave vectors.
Physics of the Solid State, 2008
The nanocomposite structure of the DLC-C 2 N condensate is confirmed by analyzing the x-ray emiss... more The nanocomposite structure of the DLC-C 2 N condensate is confirmed by analyzing the x-ray emission spectra of the CN 0 ≤ x ≤ 0.5 films prepared by pulsed arc sputtering of graphite in the presence of nitrogen.
Physics of the Solid State, 2013
The structural state of carbon in nanocomposites that are based on metals (Fe, Ni, Co, and Ag) en... more The structural state of carbon in nanocomposites that are based on metals (Fe, Ni, Co, and Ag) encapsulated in carbon and produced by the gas phase synthesis has been investigated using Raman spectros copy and high resolution transmission electron microscopy. The average diameter of particles of the initial nanocomposites after the gas phase synthesis, including the carbon shell, is less than 15 nm and can vary as a function of the conditions and regimes used for their preparation. The shell of the initial nanocomposites, irrespectively of the metal core type, consists of carbon fragments in the form of curved layers with sizes of less than 10 nm in the lateral direction. In the initial nanocomposites, there is no periodicity in the packing of carbon layers in the radial and lateral directions. The structure of the coating is assumed to be similar to the glassy carbon structure characterized by a curvature of carbon layers in different directions, which requires that, in addition to conventional hexagonal cells, the layers should contain pentagonal and heptagonal cells. Heat treatment of the initial nanocomposites Fe@C and Ni@C in butane (700°C, 60 min) not only signifi cantly increases the thickness of the carbon coating but also increases the degree of ordering of curved carbon fragments in the lateral and radial directions. In composites with Fe, Ni, and Co, along with this form of car bon, semiconducting nanotubes with a diameter of 1.3-1.5 nm are also formed. The composites with silver nanoparticles exhibit the effect of time fluctuating giant enhancement of the Raman scattering intensity.
Physics Letters A, 1990
We present polarized Raman spectra (w = 100-4000 cm-') ofa semiconducting single crystal YBa2Cu3O... more We present polarized Raman spectra (w = 100-4000 cm-') ofa semiconducting single crystal YBa2Cu3O6, that encompass the temperature range above and below TN. Significant changes occur in the phonon and high-frequency Raman spectra at temperatures from 320 to 450 K. The results imply a singularity in the electron spectrum near the Fermi energy and low-frequency excitations appear due to a rearrangement of oxygen in the structure and reduction of local symmetry by the heating.
Physical Review B, 2008
The structural disorder, heat capacity, resistivity, Hall effect, and magnetic susceptibility of ... more The structural disorder, heat capacity, resistivity, Hall effect, and magnetic susceptibility of polycrystalline chemical-vapor-deposited diamond irradiated with fast neutrons at temperature of ͑325Ϯ 10͒ K at high fluences ⌽ = ͑1-5͒ ϫ 10 20 cm −2 were investigated. Despite a significant increase in unit-cell volume ͑ϳ4.5%͒, the crystalline structure remains stable in this fluence range. The irradiation results in a paramagnetic contribution to magnetic susceptibility and to a strong ͑by 4 orders of magnitude͒ increase in heat capacity at low temperatures ͑T Ͻ 20 K͒ due to electron contribution with a T dependence characteristic of multilevel electron systems ͑the Schottky anomaly͒.
Physical Review B, 2005
The effect of pressure and temperature on the Raman-active phonon mode of osmium metal has been i... more The effect of pressure and temperature on the Raman-active phonon mode of osmium metal has been investigated for pressures up to 20 GPa and temperatures in the range 10-300 K. Under hydrostatic conditions (He pressure medium) the phonon frequency increases at a rate of 0.73(5) cm −1 /GPa (T = 300 K). A large temperature-induced and wavelength-dependent frequency shift of the phonon frequency is observed, of which only a small fraction can be associated with the thermal volume change. The main contribution to the temperature dependence of the phonon frequency is rather attributed to non-adiabatic effects in the electron-phonon interaction, which explains also the observation of an increasing phonon line width upon cooling. The phonon line width and the pressure-induced frequency shift were found to be unusually sensitive to shear stress.
physica status solidi (c), 2004
Raman spectra of single crystals of lead chalcogenides (PbTe, PbSe, PbS) were studied at room tem... more Raman spectra of single crystals of lead chalcogenides (PbTe, PbSe, PbS) were studied at room temperature and ambient pressure. The structure of spectra for all compounds is rather similar showing the bands in one-and two-phonon range. Possible spectra identification is discussed.
physica status solidi (c), 2004
The effect of pressure on the temperature dependence of the E 2g optical phonon self-energy in rh... more The effect of pressure on the temperature dependence of the E 2g optical phonon self-energy in rhenium has been investigated by Raman spectroscopy. Temperature-dependent mode Grüneisen parameters are determined. A comparison with numerical simulations of the temperature dependences of the phonon frequencies and line widths indicates pronounced changes in the electron band structure near the Fermi level under pressure.
physica status solidi (b), 2009
physica status solidi (b), 1999
The wave vector and temperature dependences of the Raman spectra have been studied for the h.c.p ... more The wave vector and temperature dependences of the Raman spectra have been studied for the h.c.p 5d transition metal Re. Two new lines were found in the spectra taken under nonresonant conditions for the allowed E 2g phonon mode. They are observed only for probing wave vector q direction along the hexagonal axis, indicating a strong interaction with charge density fluctuations coupled to the longitudinal [0001] phonon branch. The intensity of the high-frequency A 1g doublet line decreases upon heating to 300 K, its symmetry and energy are consistent with 3c superlattice formation at lower temperatures. The new low-energy mode shows a much weaker temperature dependence of its strength and is assumed to be activated in the Raman spectra due to finite probing q-magnitude.
The self-consistent linear method of augmented plane waves is used to calculate the energy band s... more The self-consistent linear method of augmented plane waves is used to calculate the energy band structure and the density of states N(E) of hexagonal technetium. A matrix element of the dipole transitions is used to calculate the frequency dependence of the interband optical conductivity U(W) and of the real part E, (a) of the complex permittivity for two directions of polarization of an optical wave relative to the hexagonal c axis of the crystal (Elc and Ellc). The anisotropy of the optical absorption is considered in the photon energy range %J = 0-25 eV. An experimental investigation is reported of the optical properties of a Tc film with the (0001 ) orientation at photon energies E = 0.62-10 eV. A strong absorption band is attributed to the (d-d,p) electron transitions. It is shown that there is a satisfactory agreement between the experimentally observed and calculated functions a, (o) and E: (w)
High Pressure Research
Pressure-induced phase transitions of lead chalcogenides were studied by Raman spectroscopy. The ... more Pressure-induced phase transitions of lead chalcogenides were studied by Raman spectroscopy. The number of Raman modes observed for the first high-pressure phases was found to be significantly less than expected from selection rules for the proposed GeS-type orthorhombic structure. The observations are consistent with the alternative assignment as CrB-type. In the case of PbS, the disappearance of the intermediate-phase Raman lines in the pressure range of 19–25 GPa, i.e., in the vicinity of the orthorhombic to CsCl-type phase transition, is accompanied by a strong increase in a structureless background. The Raman background is attributed to light scattering by charge carriers in the metallic CsCl-type phase.
Bulletin of the Russian Academy of Sciences: Physics, 2010
Silica films implanted with selenium ions (330 keV, 5 × 10 16 cm -2 ) were studied. The method of... more Silica films implanted with selenium ions (330 keV, 5 × 10 16 cm -2 ) were studied. The method of optically stimulated electron emission (OSEE) was used to analyze features specific to disordering of the film structure. Spectrum dependences of the OSEE are described in terms of the formalism of Urbach's emission rule. It was found that the discrete continuum disturbances arising upon implantation considerably distort the spectrum of the electronic and vibrational states of the SiO 2 matrix. Results of the experiment and the numerical simulation provide evidence for the activation tunneling of electrons from optically excited surface states of SiO 2 to a vacuum.
Physics of the Solid State, 2014
ABSTRACT The interaction of YBa2Cu3O6.8 (123) with water vapors at T = 200°C and the water influe... more ABSTRACT The interaction of YBa2Cu3O6.8 (123) with water vapors at T = 200°C and the water influence on the structure and electrophysical properties of the compound have been studied using Raman spectroscopy, magnetometry, and X-ray diffraction. It has been found that the penetration of water into the 123 structure leads to its transition to a hydride-oxyhydroxide H2x − z YBa2Cu3O y + x − z (OH) z containing fragments of the 124-type structure and exhibiting the spectrum of two-magnon scattering characteristic of antiferromagnetic 123 á compositions; in this case, the superconducting properties of the material as a whole are conserved. After short-time recovery annealing and subsequent oxidation, the water is removed from the compound structure, which leads to the disappearance of the spectrum of spin fluctuations. A possible mechanism of change in the 123 structure upon hydrogen and water intercalation has been discussed.
Trends in Magnetism, 2011
Features of the optical properties of nanostructured strongly correlated oxides CuO, Y 3 Fe 5 O 1... more Features of the optical properties of nanostructured strongly correlated oxides CuO, Y 3 Fe 5 O 12 , and FeBO 3 in a wide range of energies, which includes both the fundamental absorption region, low-energy electron excitations, and phonon modes have been investigated by methods of optical spectroscopy. Absorption and reflection spectra, Raman spectra, and ellipsometry measurements are carried out on the samples of oxide nanostructured ceramics. High-density nanoceramics were prepared by shock-wave loading and high pressure torsion methods from coarse-grain oxide powders. Strong smearing of the fundamental absorption edge is revealed for all nanoceramics. Anomalous red shift of the absorption edge E g is found in CuO nanooxide. The features of the optical functions in nanooxides of 3d-metals may be attributed to high defectiveness of nanooxides, peculiarities in the electronic structure of strongly correlated oxides and their tendency to electronic phase separation.
Inorganic Materials, 2006
The crystal structure of the low-temperature form of K 3 PO 4 has been determined for the first t... more The crystal structure of the low-temperature form of K 3 PO 4 has been determined for the first time using neutron diffraction (Rietveld method) and Raman spectroscopy: orthorhombic cell (sp. gr. Pnma , Z = 4), lattice parameters a = 1.12377(2) nm, b = 0.81046(1) nm, c = 0.59227(1) nm. The structure is made up of isolated [PO 4 ] tetrahedra, with the potassium ions in between.
Physics of the Solid State, 2001
The temperature dependences (5-300 K) of the Raman spectra of E 2 g phonons and optical constants... more The temperature dependences (5-300 K) of the Raman spectra of E 2 g phonons and optical constants in zinc single crystals are measured in the excitation energy range 1.4-2.54 eV. It is found that phonon damping decreases upon an increase in the wavelength of exciting radiation. The obtained results are compared with the dependence of the phonon width on the excitation energy (the probed wave vector of the excitations under investigation), which are presented for the first time for the transition metal osmium, as well as with the calculated electron-phonon renormalization of damping, taking into account the actual distribution of wave vectors.
Physics of the Solid State, 2008
The nanocomposite structure of the DLC-C 2 N condensate is confirmed by analyzing the x-ray emiss... more The nanocomposite structure of the DLC-C 2 N condensate is confirmed by analyzing the x-ray emission spectra of the CN 0 ≤ x ≤ 0.5 films prepared by pulsed arc sputtering of graphite in the presence of nitrogen.
Physics of the Solid State, 2013
The structural state of carbon in nanocomposites that are based on metals (Fe, Ni, Co, and Ag) en... more The structural state of carbon in nanocomposites that are based on metals (Fe, Ni, Co, and Ag) encapsulated in carbon and produced by the gas phase synthesis has been investigated using Raman spectros copy and high resolution transmission electron microscopy. The average diameter of particles of the initial nanocomposites after the gas phase synthesis, including the carbon shell, is less than 15 nm and can vary as a function of the conditions and regimes used for their preparation. The shell of the initial nanocomposites, irrespectively of the metal core type, consists of carbon fragments in the form of curved layers with sizes of less than 10 nm in the lateral direction. In the initial nanocomposites, there is no periodicity in the packing of carbon layers in the radial and lateral directions. The structure of the coating is assumed to be similar to the glassy carbon structure characterized by a curvature of carbon layers in different directions, which requires that, in addition to conventional hexagonal cells, the layers should contain pentagonal and heptagonal cells. Heat treatment of the initial nanocomposites Fe@C and Ni@C in butane (700°C, 60 min) not only signifi cantly increases the thickness of the carbon coating but also increases the degree of ordering of curved carbon fragments in the lateral and radial directions. In composites with Fe, Ni, and Co, along with this form of car bon, semiconducting nanotubes with a diameter of 1.3-1.5 nm are also formed. The composites with silver nanoparticles exhibit the effect of time fluctuating giant enhancement of the Raman scattering intensity.
Physics Letters A, 1990
We present polarized Raman spectra (w = 100-4000 cm-') ofa semiconducting single crystal YBa2Cu3O... more We present polarized Raman spectra (w = 100-4000 cm-') ofa semiconducting single crystal YBa2Cu3O6, that encompass the temperature range above and below TN. Significant changes occur in the phonon and high-frequency Raman spectra at temperatures from 320 to 450 K. The results imply a singularity in the electron spectrum near the Fermi energy and low-frequency excitations appear due to a rearrangement of oxygen in the structure and reduction of local symmetry by the heating.
Physical Review B, 2008
The structural disorder, heat capacity, resistivity, Hall effect, and magnetic susceptibility of ... more The structural disorder, heat capacity, resistivity, Hall effect, and magnetic susceptibility of polycrystalline chemical-vapor-deposited diamond irradiated with fast neutrons at temperature of ͑325Ϯ 10͒ K at high fluences ⌽ = ͑1-5͒ ϫ 10 20 cm −2 were investigated. Despite a significant increase in unit-cell volume ͑ϳ4.5%͒, the crystalline structure remains stable in this fluence range. The irradiation results in a paramagnetic contribution to magnetic susceptibility and to a strong ͑by 4 orders of magnitude͒ increase in heat capacity at low temperatures ͑T Ͻ 20 K͒ due to electron contribution with a T dependence characteristic of multilevel electron systems ͑the Schottky anomaly͒.
Physical Review B, 2005
The effect of pressure and temperature on the Raman-active phonon mode of osmium metal has been i... more The effect of pressure and temperature on the Raman-active phonon mode of osmium metal has been investigated for pressures up to 20 GPa and temperatures in the range 10-300 K. Under hydrostatic conditions (He pressure medium) the phonon frequency increases at a rate of 0.73(5) cm −1 /GPa (T = 300 K). A large temperature-induced and wavelength-dependent frequency shift of the phonon frequency is observed, of which only a small fraction can be associated with the thermal volume change. The main contribution to the temperature dependence of the phonon frequency is rather attributed to non-adiabatic effects in the electron-phonon interaction, which explains also the observation of an increasing phonon line width upon cooling. The phonon line width and the pressure-induced frequency shift were found to be unusually sensitive to shear stress.
physica status solidi (c), 2004
Raman spectra of single crystals of lead chalcogenides (PbTe, PbSe, PbS) were studied at room tem... more Raman spectra of single crystals of lead chalcogenides (PbTe, PbSe, PbS) were studied at room temperature and ambient pressure. The structure of spectra for all compounds is rather similar showing the bands in one-and two-phonon range. Possible spectra identification is discussed.
physica status solidi (c), 2004
The effect of pressure on the temperature dependence of the E 2g optical phonon self-energy in rh... more The effect of pressure on the temperature dependence of the E 2g optical phonon self-energy in rhenium has been investigated by Raman spectroscopy. Temperature-dependent mode Grüneisen parameters are determined. A comparison with numerical simulations of the temperature dependences of the phonon frequencies and line widths indicates pronounced changes in the electron band structure near the Fermi level under pressure.
physica status solidi (b), 2009
physica status solidi (b), 1999
The wave vector and temperature dependences of the Raman spectra have been studied for the h.c.p ... more The wave vector and temperature dependences of the Raman spectra have been studied for the h.c.p 5d transition metal Re. Two new lines were found in the spectra taken under nonresonant conditions for the allowed E 2g phonon mode. They are observed only for probing wave vector q direction along the hexagonal axis, indicating a strong interaction with charge density fluctuations coupled to the longitudinal [0001] phonon branch. The intensity of the high-frequency A 1g doublet line decreases upon heating to 300 K, its symmetry and energy are consistent with 3c superlattice formation at lower temperatures. The new low-energy mode shows a much weaker temperature dependence of its strength and is assumed to be activated in the Raman spectra due to finite probing q-magnitude.