E. Khlybov - Academia.edu (original) (raw)

Papers by E. Khlybov

Physics Letters A, 1988

ABSTRACT The temperature dependent splitting of spectral lines in the optical spectra of Y2BaCuO5... more ABSTRACT The temperature dependent splitting of spectral lines in the optical spectra of Y2BaCuO5-Er (1 at%) is reported. It is interpreted as a result of the splitting of Er3+ Kramers doublets in a local magnetic field which appears due to some kind of magnetic ordering in the nonsuperconducting green phase Y2BaCuO5 of the Y-Ba-Cu-O high Tc system.

Journal of Superconductivity and Novel Magnetism, 2013

The 57 Fe-Mössbauer spectroscopy measurements on the polycrystalline superconductor GdO 0.88 F 0.... more The 57 Fe-Mössbauer spectroscopy measurements on the polycrystalline superconductor GdO 0.88 F 0.12 FeAs with the bulk critical temperature T C = 53 K were carried out at temperatures between 5 and 300 K. Two nonequivalent Fe 2+ sites were revealed in the Fe-As superconducting planes. Iron ions show clear nonmagnetic behavior in all temperature ranges. There were no observed significant changes in the hyperfine Mössbauer parameters below and above T C . The magnetic component appearing below 75 K indicates the presence of a small fraction of impurity phase FeAs.

Acta Crystallographica Section A Foundations of Crystallography, 1996

The study of the temperature variation of the electrical resistivity and the current-voltage char... more The study of the temperature variation of the electrical resistivity and the current-voltage characteristics of phases in the La-Sr-Ti-O, La-Sr-Nb-O, La-Mn-O, Ba-Sr-Pb-O, La-Pb-Re-O, Mg-Ti-O systems suggests that some compositions contain superconducting inclusions. The structure of superconducting inclusions (structure fragments) is coherently connected with structure of the non-superconducting phase and has different composition from one. A similar phenomenon was observed in samples of the well-known system YBa2Cu3O6+when increased from 0.2 to 0.5. The phases of compositions (Ln,Sr) x NbO3- (La,Sr) x TiO3-(La,Pb) x ReO3- belonging to cubic bronzes of perovskite contain superconducting structure fragments with Tci =160 K, 50 K and 60 K, respectively. The phases (Ba,Sr)PbO3 (perovskite structures) with Tci =70 K and Mg(Mg,Ti)O4spinel structure)withTci =130 K have the cubic symmetry. There are indications of the possible presence of superconducting fragments with Tci =180 K in the phase LaMnO3+  with rhombohedral perovskite structure. The dependence of the critical temperature of the superconducting phases, Tc, and inclusions, Tci, on formal charge of Ti, Nb, Pb, Re, Mn, Bi, Cu cations is found.

Inorganic Materials, 2005

Journal of Experimental and Theoretical Physics

The properties of the superconducting state of bulk samples of ternary molybdenum sulfides contai... more The properties of the superconducting state of bulk samples of ternary molybdenum sulfides containing copper, tin, and lead were investigated. The highest values of all three critical parameters T,, H,,, and J, were observed in compounds with lead. Variation of the annealing temperature from 720 to 1120' Cat one and the same annealing time (24 h) leads to a change in the density of the critical current in Pb, ,Mo,,S, samples by more than one order of magnitude, whereas the remaining critical parameters undergo changes in the range of 40%. The maximum critical-current density J,(140 kOe; 1.7 K) = 3.5 x 10' A/m2 is reached at an annealing temperature 92W C. The connection between the shapes of the J, (H, T = const) curves and the damping rate of the critical current in hollow cylindrical samples is analyzed.

Journal of Experimental and Theoretical Physics

Results are presented of an investigation of the electrical and magnetic properties of specimens ... more Results are presented of an investigation of the electrical and magnetic properties of specimens of various compositions belonging to the R-Ba-Cu-0, Bi-Sr-Ca-Cu-0 and Tl-Ba-Ca-Cu-0 systems (where R are rare earth elements or yttrium). On lowering the temperature below 180 K the temperature dependences of the electrical resistance ρ(T) and of the magnetic susceptibility χ(T) are found to change in most of the superconducting (T_c > 80 K), practically single-phase, specimens. It is shown that along with thermodynamic fluctuations, a significant contribution to ρ(T) and χ(T) may come from impurity phases with values of T_c higher than those of the main phase. Their presence is confirmed by both x-ray data and measurement of the magnetic and electrical properties. Thus, for example, in some of the multiphase samples there are in the ρ(T) dependence reproducible smoothened steps which extend up to 160 K. It is found that for each system the increase in Tc is accompanied by a decrease ...

The Andreev reflection spectra were studied for the first time in the magnetic superconductor Dy0... more The Andreev reflection spectra were studied for the first time in the magnetic superconductor Dy0.6Y0.4Rh3.85Ru0.15B4. It is found that an external magnetic field (up to 0.7 Hc2) is a strong stimulator of superconductivity in contrast with traditional superconductors with a singlet pairing. The ratio 2\Delta/kBTc \approx 4.0 obtained for some contacts is higher than the value 3.52 which is typical of conventional superconductors with a weak electron-phonon interaction. It has been proposed that in Dy0.6Y0.4Rh3.85Ru0.15B4 a triplet mechanism of superconducting pairing is realized.

Physica B: Condensed Matter, 2001

A series of polycrystalline samples of system TlA RCu O \V (A"Sr, Ba; R"RE, Y and Ca) with perovs... more A series of polycrystalline samples of system TlA RCu O \V (A"Sr, Ba; R"RE, Y and Ca) with perovskite-like 1212-structure has been synthesized and investigated by magnetic and transport measurements in the temperature range of 4.2}300 K. The measurements revealed that along with high-temperature superconductivity, some of these compounds exhibit spontaneous antiferromagnetism, "eld-induced antiferromagnetism or ferromagnetism. Di!erent types of magnetic ordering have been found depending on rare-earth ions located in R position. The phenomenon of phase separation to magnetic and superconducting phases has probably been observed in a number of compounds.

ABSTRACT This paper describes syntheses and structure and composition refinement for phases of th... more ABSTRACT This paper describes syntheses and structure and composition refinement for phases of the general composition (In,Cu)Sr2YCu2O6 + d (1212) and (In,Cu)(Sr,Ho)2(Ho,Ce)2O8 + d (1222) obtained in air atmosphere and for the same phases treated in oxygen. Oxygen treatment did not change the oxygen content in the phases, but changed the composition of the cationic (especially In) sites. The absence of superconductivity is explained by the nonoptimal values of the formal charge of copper [FC(Cu)] obtained from the electroneutrality condition and taking into account the refined phase compositions. Superconductivity found for the phase of composition (In,Cu)Ba2(Y,Ca)Cu2O6 + d (Tc = 80 K) is lost when the sample is annealed in air and during subsequent thermobaric treatment, leading to changes in the oxygen and indium contents and to a decrease in FC(Cu) from ~2.15 to 2.05 and 2.08, respectively.

ABSTRACT A series of infinite-layer compounds Nd x Sr1–x CuO2 were synthesized by high-pressure t... more ABSTRACT A series of infinite-layer compounds Nd x Sr1–x CuO2 were synthesized by high-pressure technique under different pressure, temperature, and time conditions. Crystal structure, microstructure, and superconducting properties of the samples obtained were systematically investigated as a function of the synthesis conditions. The stability of the IL phase was studied using annealing procedures in Ar- and O2-flow, as well as under oxygen pressure up to 90 bar followed by thermogravimetric, energy-dispersive X-ray analysis, and X-ray diffraction measurements. On the basis of the results obtained we suggest a decomposition mechanism for the infinite-layer phase, which is responsible for the degradation of T c , as well as a routine to produce electron-doped infinite-layer compounds with a sharp diamagnetic signal of bulk superconductivity.

Physics Letters A, 1988

ABSTRACT The temperature dependent splitting of spectral lines in the optical spectra of Y2BaCuO5... more ABSTRACT The temperature dependent splitting of spectral lines in the optical spectra of Y2BaCuO5-Er (1 at%) is reported. It is interpreted as a result of the splitting of Er3+ Kramers doublets in a local magnetic field which appears due to some kind of magnetic ordering in the nonsuperconducting green phase Y2BaCuO5 of the Y-Ba-Cu-O high Tc system.

Journal of Superconductivity and Novel Magnetism, 2013

The 57 Fe-Mössbauer spectroscopy measurements on the polycrystalline superconductor GdO 0.88 F 0.... more The 57 Fe-Mössbauer spectroscopy measurements on the polycrystalline superconductor GdO 0.88 F 0.12 FeAs with the bulk critical temperature T C = 53 K were carried out at temperatures between 5 and 300 K. Two nonequivalent Fe 2+ sites were revealed in the Fe-As superconducting planes. Iron ions show clear nonmagnetic behavior in all temperature ranges. There were no observed significant changes in the hyperfine Mössbauer parameters below and above T C . The magnetic component appearing below 75 K indicates the presence of a small fraction of impurity phase FeAs.

Acta Crystallographica Section A Foundations of Crystallography, 1996

The study of the temperature variation of the electrical resistivity and the current-voltage char... more The study of the temperature variation of the electrical resistivity and the current-voltage characteristics of phases in the La-Sr-Ti-O, La-Sr-Nb-O, La-Mn-O, Ba-Sr-Pb-O, La-Pb-Re-O, Mg-Ti-O systems suggests that some compositions contain superconducting inclusions. The structure of superconducting inclusions (structure fragments) is coherently connected with structure of the non-superconducting phase and has different composition from one. A similar phenomenon was observed in samples of the well-known system YBa2Cu3O6+when increased from 0.2 to 0.5. The phases of compositions (Ln,Sr) x NbO3- (La,Sr) x TiO3-(La,Pb) x ReO3- belonging to cubic bronzes of perovskite contain superconducting structure fragments with Tci =160 K, 50 K and 60 K, respectively. The phases (Ba,Sr)PbO3 (perovskite structures) with Tci =70 K and Mg(Mg,Ti)O4spinel structure)withTci =130 K have the cubic symmetry. There are indications of the possible presence of superconducting fragments with Tci =180 K in the phase LaMnO3+  with rhombohedral perovskite structure. The dependence of the critical temperature of the superconducting phases, Tc, and inclusions, Tci, on formal charge of Ti, Nb, Pb, Re, Mn, Bi, Cu cations is found.

Inorganic Materials, 2005

Journal of Experimental and Theoretical Physics

The properties of the superconducting state of bulk samples of ternary molybdenum sulfides contai... more The properties of the superconducting state of bulk samples of ternary molybdenum sulfides containing copper, tin, and lead were investigated. The highest values of all three critical parameters T,, H,,, and J, were observed in compounds with lead. Variation of the annealing temperature from 720 to 1120' Cat one and the same annealing time (24 h) leads to a change in the density of the critical current in Pb, ,Mo,,S, samples by more than one order of magnitude, whereas the remaining critical parameters undergo changes in the range of 40%. The maximum critical-current density J,(140 kOe; 1.7 K) = 3.5 x 10' A/m2 is reached at an annealing temperature 92W C. The connection between the shapes of the J, (H, T = const) curves and the damping rate of the critical current in hollow cylindrical samples is analyzed.

Journal of Experimental and Theoretical Physics

Results are presented of an investigation of the electrical and magnetic properties of specimens ... more Results are presented of an investigation of the electrical and magnetic properties of specimens of various compositions belonging to the R-Ba-Cu-0, Bi-Sr-Ca-Cu-0 and Tl-Ba-Ca-Cu-0 systems (where R are rare earth elements or yttrium). On lowering the temperature below 180 K the temperature dependences of the electrical resistance ρ(T) and of the magnetic susceptibility χ(T) are found to change in most of the superconducting (T_c > 80 K), practically single-phase, specimens. It is shown that along with thermodynamic fluctuations, a significant contribution to ρ(T) and χ(T) may come from impurity phases with values of T_c higher than those of the main phase. Their presence is confirmed by both x-ray data and measurement of the magnetic and electrical properties. Thus, for example, in some of the multiphase samples there are in the ρ(T) dependence reproducible smoothened steps which extend up to 160 K. It is found that for each system the increase in Tc is accompanied by a decrease ...

The Andreev reflection spectra were studied for the first time in the magnetic superconductor Dy0... more The Andreev reflection spectra were studied for the first time in the magnetic superconductor Dy0.6Y0.4Rh3.85Ru0.15B4. It is found that an external magnetic field (up to 0.7 Hc2) is a strong stimulator of superconductivity in contrast with traditional superconductors with a singlet pairing. The ratio 2\Delta/kBTc \approx 4.0 obtained for some contacts is higher than the value 3.52 which is typical of conventional superconductors with a weak electron-phonon interaction. It has been proposed that in Dy0.6Y0.4Rh3.85Ru0.15B4 a triplet mechanism of superconducting pairing is realized.

Physica B: Condensed Matter, 2001

A series of polycrystalline samples of system TlA RCu O \V (A"Sr, Ba; R"RE, Y and Ca) with perovs... more A series of polycrystalline samples of system TlA RCu O \V (A"Sr, Ba; R"RE, Y and Ca) with perovskite-like 1212-structure has been synthesized and investigated by magnetic and transport measurements in the temperature range of 4.2}300 K. The measurements revealed that along with high-temperature superconductivity, some of these compounds exhibit spontaneous antiferromagnetism, "eld-induced antiferromagnetism or ferromagnetism. Di!erent types of magnetic ordering have been found depending on rare-earth ions located in R position. The phenomenon of phase separation to magnetic and superconducting phases has probably been observed in a number of compounds.

ABSTRACT This paper describes syntheses and structure and composition refinement for phases of th... more ABSTRACT This paper describes syntheses and structure and composition refinement for phases of the general composition (In,Cu)Sr2YCu2O6 + d (1212) and (In,Cu)(Sr,Ho)2(Ho,Ce)2O8 + d (1222) obtained in air atmosphere and for the same phases treated in oxygen. Oxygen treatment did not change the oxygen content in the phases, but changed the composition of the cationic (especially In) sites. The absence of superconductivity is explained by the nonoptimal values of the formal charge of copper [FC(Cu)] obtained from the electroneutrality condition and taking into account the refined phase compositions. Superconductivity found for the phase of composition (In,Cu)Ba2(Y,Ca)Cu2O6 + d (Tc = 80 K) is lost when the sample is annealed in air and during subsequent thermobaric treatment, leading to changes in the oxygen and indium contents and to a decrease in FC(Cu) from ~2.15 to 2.05 and 2.08, respectively.

ABSTRACT A series of infinite-layer compounds Nd x Sr1–x CuO2 were synthesized by high-pressure t... more ABSTRACT A series of infinite-layer compounds Nd x Sr1–x CuO2 were synthesized by high-pressure technique under different pressure, temperature, and time conditions. Crystal structure, microstructure, and superconducting properties of the samples obtained were systematically investigated as a function of the synthesis conditions. The stability of the IL phase was studied using annealing procedures in Ar- and O2-flow, as well as under oxygen pressure up to 90 bar followed by thermogravimetric, energy-dispersive X-ray analysis, and X-ray diffraction measurements. On the basis of the results obtained we suggest a decomposition mechanism for the infinite-layer phase, which is responsible for the degradation of T c , as well as a routine to produce electron-doped infinite-layer compounds with a sharp diamagnetic signal of bulk superconductivity.