Markus Peurla | University of Turku (original) (raw)

Papers by Markus Peurla

Research paper thumbnail of Heterogeneous catalysis for transformation of biomass derived compounds beyond fuels: Synthesis of monoterpenoid dioxinols with analgesic activity

Journal of Molecular Catalysis A: Chemical, 2015

Catalytic synthesis of a dioxinol compound, (2S,4aR,8R,8aR)-4,4,7-trimethyl-2-phenyl-4a,5,8,8atet... more Catalytic synthesis of a dioxinol compound, (2S,4aR,8R,8aR)-4,4,7-trimethyl-2-phenyl-4a,5,8,8atetrahydro-4H-benzo[d][1,3]dioxin-8-ol, exhibiting analgesic activity was demonstrated over Femodified beta zeolite. During interactions between cis-verbenol oxide and benzaldehyde, two main reactions occurred. In the first reaction, namely isomerization of verbenol oxide both cyclopentenic hydroxyketone, oxetane as well as a cyclohexyl compound, (1R,2R,6S)-3-methyl-6-(prop-1-en-2yl)cyclohex-3-ene-1,2-diol were formed. In the second parallel reaction the target compound was generated. The highest yield of the target compound was achieved in the reaction between verbenol oxide and benzaldehyde at their molar ratio of 1:133 with the bifunctional iron modified Fe-H-Beta-150 catalyst at 70 • C giving a much higher yield than reported earlier in the literature, being 46 mol-% at complete conversion of verbenol oxide.

Research paper thumbnail of Preparation of selective ZnCl2/alumina catalysts for methyl chloride synthesis: Influence of pH, precursor and zinc loading

Applied Catalysis A: General, 2015

ABSTRACT Zinc-modified alumina catalysts for methyl chloride synthesis were prepared with varying... more ABSTRACT Zinc-modified alumina catalysts for methyl chloride synthesis were prepared with varying zinc loadings: from 2.4 to 21.1 wt%. The influence of the zinc loading, zinc precursor and the pH of the impregnation on the physico-chemical properties of the catalyst, and on the catalyst activity and selectivity for methyl chloride (MeCl) synthesis was investigated. The prepared catalysts were thoroughly characterized by FTIR, TEM, physisorption and EDX. On the alumina surface, both molecular and bulk zinc species are created upon zinc loading. The surface area of the catalyst decreases steadily with zinc loading. Bulk zinc species dominate on the catalyst starting at a zinc loading of 9.4 wt% and the amount of Lewis acid sites (LAS) decreases. A shift in the acid site type takes place upon zinc modification. Sites assigned to stronger LAS are eliminated while zinc-based weaker acid sites started to predominate. The shift in acidity increases the selectivity and activity of methyl chloride synthesis, which was demonstrated in a series of experiments in a laboratory-scale fixed bed reactor.

Research paper thumbnail of Benefits of Using a Nanostructured Target in Laser Ablation of Thin YBCO Films

Ceramic Transactions Series, 2006

Research paper thumbnail of Magnetic relaxation and flux pinning in YBCO films prepared by PLD from a nanocrystalline target

Superconductor Science and Technology, 2005

The magnetic flux pinning properties of YBCO films prepared by pulsed laser deposition from nano-... more The magnetic flux pinning properties of YBCO films prepared by pulsed laser deposition from nano- (n) and microcrystalline (mu) targets are studied and compared by magnetic relaxation and hysteresis measurements. The most striking difference between the films is the higher critical current density of the n-films (Jc(0 T,77 K) = 1 × 107 A cm-2) compared to the mu-films (Jc(0

Research paper thumbnail of Optimization of the BaZrO 3 concentration in YBCO films prepared by pulsed laser deposition

Superconductor Science and Technology, 2006

YBCO films were prepared by pulsed laser deposition from nanocrystalline targets doped with diffe... more YBCO films were prepared by pulsed laser deposition from nanocrystalline targets doped with different concentrations of BaZrO3 ranging from c = 0.9 to 9.0 wt%. The critical temperature of the films decreases almost linearly with increasing BaZrO3 content whereas the critical current density shows a maximum near 3.9 wt%. In comparison with undoped YBCO films the accommodation field B* is

Research paper thumbnail of Crystalline orientation and twin formation in YBCO thin films laser ablated from a nanocrystalline target

Superconductor Science and Technology, 2004

Two sets of superconducting thin films were deposited on SrTiO3 by laser ablation, the first usin... more Two sets of superconducting thin films were deposited on SrTiO3 by laser ablation, the first using a nanocrystalline target (n-films) and the second using a commercial microcrystalline target (mgr-films). The effect of film thickness on the structure of the films was investigated using detailed x-ray diffraction analysis. It was found that for both types of film growth is a three-phase process, where at the beginning some grains with their a-axis perpendicular to the substrate surface are formed. In the second phase a purely c-axis oriented film is formed and in the last phase some a-axis oriented grains are again observed. The last phase was observed only for the mgr-films. Both types of film were found to have equal numbers of c-axis oriented grains oriented with their a-axis to the phgr = 0° and to the 90° direction. It was also found that the twin structure observed in both types of film develops much faster in the n-films, which might be the reason for the observed high critical current densities in n-films.

Research paper thumbnail of Experimental study of the magnetosuperconductor RuSr2Eu1.5Ce0.5Cu2O10−δ: Effect of Mo doping on magnetic behavior and Tc variation

Physical Review B, 2006

Mo doped ruthenocuprates Ru 1-x Mo x Sr 2 Eu 1.5 Ce 0.5 Cu 2 O 10-δ are synthesized for x = 0.0, ... more Mo doped ruthenocuprates Ru 1-x Mo x Sr 2 Eu 1.5 Ce 0.5 Cu 2 O 10-δ are synthesized for x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0, and their magnetic and superconducting properties are studied. It has been found that the magnetic transition temperature T ZFC peak , which corresponds to the appearance of weak ferromagnetic effect, decreases from its value of 75 K for x = 0.0 to 22 K, 25 K and 18 K, respectively for the x = 0.2, 0.4 and 0.6 samples. Another finding is that the magnetic susceptibility reduces at T ZFC peak by a factor of about 6, 85 and 413 for x = 0.2, 0.4, and 0.6 respectively. The samples of x = 0.8 and 1.0 are found to have no magnetic or superconducting effects. The values of the superconducting transition temperature are obtained from the resistivity versus temperature data. An important result is that T c increases by 4.5 K and 7.0 K for x = 0.2 and 0.4 respectively, and then decreases by 17 K for x = 0.6. The observed variation of T c with x has been explained in terms of a theory which combines the effects of weakening magnetic behavior and reducing carrier concentration in a phenomenological manner. The resulting theory is found to provide a good agreement with the observed value of T c .

Research paper thumbnail of Magnetic field dependence of the critical current and the flux pinning mechanism in YBa2Cu3O6+x films doped with BaZrO3

Research paper thumbnail of Effects of nanocrystalline target and columnar defects on flux pinning in pure and BaZrO3-doped YBa2Cu3O6+x films in fields up to 30T

Research paper thumbnail of Dependence of critical current density on crystalline direction in thin YBCO films

Physica C: Superconductivity, 2005

ABSTRACT The dependence of critical current density (Jc) on the angle between the current directi... more ABSTRACT The dependence of critical current density (Jc) on the angle between the current direction and the (1 0 0) direction in the ab-plane of thin YBCO films deposited on (0 0 1)-SrTiO3 from nanocrystalline and microcrystalline targets is studied using magneto-optical microscopy. In the films made from the nanocrystalline target it is found that Jc does not depend on the angle whereas Jc decreases with increasing angle in the films made from the microcrystalline target. The films were characterized by detailed X-ray diffraction measurements. The findings are explained in terms of a network of planar defects indicating that in addition to linear defects also the twin boundaries are very important flux pinning sites.

Research paper thumbnail of High pinning potential in YBCO thin films deposited from a target prepared from YBCO nanopowder

Physica C: Superconductivity, 2004

ABSTRACT Thin YBa2Cu3O6+x (YBCO) films were prepared on SrTiO3 substrates by pulsed laser deposit... more ABSTRACT Thin YBa2Cu3O6+x (YBCO) films were prepared on SrTiO3 substrates by pulsed laser deposition using a target made from nanosized powder. These films show high critical current densities Jc≈1×107 A/cm2 at 77 K in zero field as obtained by SQUID magnetization measurements. The pinning potentials, U(T), were calculated from the magnetic relaxation curves measured at several temperatures after cooling the sample in 1 T. From these data the U(0 K) was extrapolated to be 900 K, which is higher than previously reported for as-prepared films.

Research paper thumbnail of Anisotropic pinning defects in BaZrO3-doped YBa2Cu3O6+x films in high magnetic fields

Physica C: Superconductivity, 2008

Angular dependence of the resistivity, the irreversibility field and the critical current of undo... more Angular dependence of the resistivity, the irreversibility field and the critical current of undoped and BaZrO3-(BZO)-doped YBa2Cu3O6+x (YBCO) thin films are investigated using pulsed magnetic fields up to 30T. Doping with BZO forms a dense network of anisotropic c-axis oriented columnar defects, which lead, in comparison with undoped material, to clearly improved values of the pinning potential, the critical current

Research paper thumbnail of Improvement of superconducting properties of old Y–Ba–Cu–O specimens by high-energy heavy ion irradiation

Physica C: Superconductivity, 2006

ABSTRACT Superconducting parameters of different, almost 20 years old Y–Ba–Cu–O samples, prepared... more ABSTRACT Superconducting parameters of different, almost 20 years old Y–Ba–Cu–O samples, prepared in 1987–1988 are investigated. The aim of this research is to find out how a heavy ion beam can enhance the superconducting features of very old and originally not always perfect Y-based specimens. As is observed, their electrical and magnetic characteristics are very sensitive to high-energy Bi-ion irradiation, which results in significant increase of the superconducting parameters. The most important one of them is the global critical current density which is calculated with the help of a new method on the basis of experiments. It can be increased by 18–39%, depending on the original, starting conditions of the samples before the irradiation. At the same time, the average values of intragrain critical current density grows by 37–51%. A slight increase in the critical temperature of 1–2 K was also observed. The experiments on AC susceptibility demonstrate that this irradiation causes to develop faster the total diamagnetic state and decreases the loss. The reason of these effects can be found in the better orientation of crystals, enlargement of microcrystalline aggregates, higher homogenization of the material, thus, in the increase of the superconducting component of samples due to the irradiation.

Research paper thumbnail of Anomalous lattice expansion of RuSr2Eu1.5Ce0.5Cu2O10−δ (Ru-1222) magneto superconductor: A low temperature X-ray diffraction study

Physica C: Superconductivity, 2006

Detailed X-ray diffraction studies on RuSr 2 Eu 1.5 Ce 0.5 Cu 2 O 10-δ (Eu-Ru-1222) magneto super... more Detailed X-ray diffraction studies on RuSr 2 Eu 1.5 Ce 0.5 Cu 2 O 10-δ (Eu-Ru-1222) magneto superconductor down to 13 K at close temperature intervals revealed that with decreasing temperature, the c-parameter decreases linearly down to 100 K, following the relation c = 28.412(1) + 2.5(1)x10 -4 T and then becomes almost temperature independent on further lowering of temperature. Interestingly, the linear decrease in the a-parameter is seen only up to 180 K. Below 180 K, the observed values of the a-parameters are more than the value expected from the linear variation. This departure can be considered as development of strain in the 2 system. Interestingly enough, these temperatures coincide with the complex magnetic ordering (T mag ) of Ru in Ru-1222 system. This is the first report of the observation of the onset of excess volume and also of the strain along the a-axis near the magnetic ordering temperature in Ru-1222 superconductor, and indicates a coupling between the lattice and the magnetism in this system. Magnetization, magneto transport and thermoelectric power measurements being carried out on the same sample are also reported. The results of low temperature excess volume and the strain along a -axis of Ru-1222 compound are reportedly not seen in Ru-1212 (RuSr 2 GdCu 2 O 8 ).

Research paper thumbnail of Magnetism, upper critical field and thermoelectric power of the magnetosuperconductor RuSr 2 Eu 1.5 Ce 0.5 Cu 2 O 10−δ

Journal of Physics: Condensed Matter, 2006

Magnetic susceptibility, M-H plot, magnetoresistance and thermoelectric power of the RuSr 2 Eu 1.... more Magnetic susceptibility, M-H plot, magnetoresistance and thermoelectric power of the RuSr 2 Eu 1.5 Ce 0.5 Cu 2 O 10-δ superconductor are measured. Values of the magnetic transition temperature T mag , superconductivity transition temperature T c , upper critical field H c2 , chemical potential µ, and energy width for electric conduction W σ are obtained from these measurements. It has been found that T mag = 140 K, T c = 25 K (33 K) from susceptibility (magnetoresistance) measurements, H c2 (0) > 32 T, µ = 8 meV, and W σ = 58.5 meV. These values are compared with other ruthenate superconductors, and resulting physical information is discussed.

Research paper thumbnail of Superconducting Properties of Films Deposited From Micro-, Nanocrystalline and Optimally BZO-Doped YBCO Targets

IEEE Transactions on Applied Superconductivity, 2000

Thin YBa2Cu3O6+x (YBCO) films are prepared by pulsed laser deposition (PLD) from pure micro- (mu)... more Thin YBa2Cu3O6+x (YBCO) films are prepared by pulsed laser deposition (PLD) from pure micro- (mu) and nanocrystalline (n) targets and a n-target optimally doped with 3.9 wt% BaZrO3 (BZO). Effects of target grain size and doping on superconducting (SC) properties of the films are investigated using a SQUID magnetometer up to 5 T and transport measurements in pulsed magnetic fiefds

Research paper thumbnail of YBCO Films Prepared by PLD Using Nanocrystalline Targets Doped With<tex>$hboxBaZrO_3$</tex>or Y211

IEEE Transactions on Appiled Superconductivity, 2005

YBCO thin films were prepared by pulsed laser deposition from a pure nanocrystalline YBCO target ... more YBCO thin films were prepared by pulsed laser deposition from a pure nanocrystalline YBCO target and similar targets doped with BaZrO3 or Y2BaCuO5 (Y211 phase) in order to investigate the effect of these impurities on magnetic flux pinning. The doped targets were pressed from nanopowders prepared by a sol-gel method from starting solutions whose nominal molar ratios corresponded to compositions

Research paper thumbnail of Structural Properties of YBCO Thin Films Deposited From Different Kinds of Targets

IEEE Transactions on Applied Superconductivity, 2000

The accommodation field of YBa2Cu3O6+infin (YBCO) a thin films depends on the microstructure of t... more The accommodation field of YBa2Cu3O6+infin (YBCO) a thin films depends on the microstructure of the films and specifically the amount of pinning sites, which can be controlled by the type of the target used in the laser deposition. Typical values for the accommodation field at 5 K are 40-100 mT, 160 mT and 500 mT for films deposited from a

Research paper thumbnail of Curcumin Associated Poly (Allylamine Hydrochloride)-Phosphate Self-Assembled Hierarchically Ordered Nanocapsules: Size Dependent Investigation on Release and DPPH Scavenging Activity of Curcumin

RSC Adv., 2015

Combination of a cationic polyamine with a multivalent anionic salt results in the spontaneous ge... more Combination of a cationic polyamine with a multivalent anionic salt results in the spontaneous generation of ionically crosslinked capsules. Here we report curcumin associated poly(allylamine hydrochloride) crosslinks with dipotassium phosphate and subsequently congregates with silica nanoparticles to form hierarchically ordered nanocapsule structures. The capsule sizes vary depending on the concentration of dipotassium phosphate. SEM data ascertain the spherical shape of the nanocapsules and TEM analysis demonstrates that the outer layer made up of silica has a thickness of $50-250 nm. The fluorescence images confirm that curcumin are present all over the capsules. Strong interaction between nanocapsules and curcumin is evident from spectroscopic analysis and TGA data. Release of curcumin from the nanocapsules is found to be triggered by pH where basic environment trigger the maximum release compared to acidic and neutral conditions. The drug release profile of curcumin from the nanocapsules follows the Higuchi model and depends on the size of the nanocapsules. 2,2-Diphenyl-1picrylhydrazyl (DPPH) scavenging activity of the encapsulated curcumin decreases exponentially with a decrease in size of the nanocapsules, suggesting not only weight percentage of curcumin in the nanocapsules plays a role but also availability of b-diketone group of curcumin for H-donation is vital.

Research paper thumbnail of Heterogeneous catalysis for transformation of biomass derived compounds beyond fuels: Synthesis of monoterpenoid dioxinols with analgesic activity

Journal of Molecular Catalysis A: Chemical, 2015

Catalytic synthesis of a dioxinol compound, (2S,4aR,8R,8aR)-4,4,7-trimethyl-2-phenyl-4a,5,8,8atet... more Catalytic synthesis of a dioxinol compound, (2S,4aR,8R,8aR)-4,4,7-trimethyl-2-phenyl-4a,5,8,8atetrahydro-4H-benzo[d][1,3]dioxin-8-ol, exhibiting analgesic activity was demonstrated over Femodified beta zeolite. During interactions between cis-verbenol oxide and benzaldehyde, two main reactions occurred. In the first reaction, namely isomerization of verbenol oxide both cyclopentenic hydroxyketone, oxetane as well as a cyclohexyl compound, (1R,2R,6S)-3-methyl-6-(prop-1-en-2yl)cyclohex-3-ene-1,2-diol were formed. In the second parallel reaction the target compound was generated. The highest yield of the target compound was achieved in the reaction between verbenol oxide and benzaldehyde at their molar ratio of 1:133 with the bifunctional iron modified Fe-H-Beta-150 catalyst at 70 • C giving a much higher yield than reported earlier in the literature, being 46 mol-% at complete conversion of verbenol oxide.

Research paper thumbnail of Preparation of selective ZnCl2/alumina catalysts for methyl chloride synthesis: Influence of pH, precursor and zinc loading

Applied Catalysis A: General, 2015

ABSTRACT Zinc-modified alumina catalysts for methyl chloride synthesis were prepared with varying... more ABSTRACT Zinc-modified alumina catalysts for methyl chloride synthesis were prepared with varying zinc loadings: from 2.4 to 21.1 wt%. The influence of the zinc loading, zinc precursor and the pH of the impregnation on the physico-chemical properties of the catalyst, and on the catalyst activity and selectivity for methyl chloride (MeCl) synthesis was investigated. The prepared catalysts were thoroughly characterized by FTIR, TEM, physisorption and EDX. On the alumina surface, both molecular and bulk zinc species are created upon zinc loading. The surface area of the catalyst decreases steadily with zinc loading. Bulk zinc species dominate on the catalyst starting at a zinc loading of 9.4 wt% and the amount of Lewis acid sites (LAS) decreases. A shift in the acid site type takes place upon zinc modification. Sites assigned to stronger LAS are eliminated while zinc-based weaker acid sites started to predominate. The shift in acidity increases the selectivity and activity of methyl chloride synthesis, which was demonstrated in a series of experiments in a laboratory-scale fixed bed reactor.

Research paper thumbnail of Benefits of Using a Nanostructured Target in Laser Ablation of Thin YBCO Films

Ceramic Transactions Series, 2006

Research paper thumbnail of Magnetic relaxation and flux pinning in YBCO films prepared by PLD from a nanocrystalline target

Superconductor Science and Technology, 2005

The magnetic flux pinning properties of YBCO films prepared by pulsed laser deposition from nano-... more The magnetic flux pinning properties of YBCO films prepared by pulsed laser deposition from nano- (n) and microcrystalline (mu) targets are studied and compared by magnetic relaxation and hysteresis measurements. The most striking difference between the films is the higher critical current density of the n-films (Jc(0 T,77 K) = 1 × 107 A cm-2) compared to the mu-films (Jc(0

Research paper thumbnail of Optimization of the BaZrO 3 concentration in YBCO films prepared by pulsed laser deposition

Superconductor Science and Technology, 2006

YBCO films were prepared by pulsed laser deposition from nanocrystalline targets doped with diffe... more YBCO films were prepared by pulsed laser deposition from nanocrystalline targets doped with different concentrations of BaZrO3 ranging from c = 0.9 to 9.0 wt%. The critical temperature of the films decreases almost linearly with increasing BaZrO3 content whereas the critical current density shows a maximum near 3.9 wt%. In comparison with undoped YBCO films the accommodation field B* is

Research paper thumbnail of Crystalline orientation and twin formation in YBCO thin films laser ablated from a nanocrystalline target

Superconductor Science and Technology, 2004

Two sets of superconducting thin films were deposited on SrTiO3 by laser ablation, the first usin... more Two sets of superconducting thin films were deposited on SrTiO3 by laser ablation, the first using a nanocrystalline target (n-films) and the second using a commercial microcrystalline target (mgr-films). The effect of film thickness on the structure of the films was investigated using detailed x-ray diffraction analysis. It was found that for both types of film growth is a three-phase process, where at the beginning some grains with their a-axis perpendicular to the substrate surface are formed. In the second phase a purely c-axis oriented film is formed and in the last phase some a-axis oriented grains are again observed. The last phase was observed only for the mgr-films. Both types of film were found to have equal numbers of c-axis oriented grains oriented with their a-axis to the phgr = 0° and to the 90° direction. It was also found that the twin structure observed in both types of film develops much faster in the n-films, which might be the reason for the observed high critical current densities in n-films.

Research paper thumbnail of Experimental study of the magnetosuperconductor RuSr2Eu1.5Ce0.5Cu2O10−δ: Effect of Mo doping on magnetic behavior and Tc variation

Physical Review B, 2006

Mo doped ruthenocuprates Ru 1-x Mo x Sr 2 Eu 1.5 Ce 0.5 Cu 2 O 10-δ are synthesized for x = 0.0, ... more Mo doped ruthenocuprates Ru 1-x Mo x Sr 2 Eu 1.5 Ce 0.5 Cu 2 O 10-δ are synthesized for x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0, and their magnetic and superconducting properties are studied. It has been found that the magnetic transition temperature T ZFC peak , which corresponds to the appearance of weak ferromagnetic effect, decreases from its value of 75 K for x = 0.0 to 22 K, 25 K and 18 K, respectively for the x = 0.2, 0.4 and 0.6 samples. Another finding is that the magnetic susceptibility reduces at T ZFC peak by a factor of about 6, 85 and 413 for x = 0.2, 0.4, and 0.6 respectively. The samples of x = 0.8 and 1.0 are found to have no magnetic or superconducting effects. The values of the superconducting transition temperature are obtained from the resistivity versus temperature data. An important result is that T c increases by 4.5 K and 7.0 K for x = 0.2 and 0.4 respectively, and then decreases by 17 K for x = 0.6. The observed variation of T c with x has been explained in terms of a theory which combines the effects of weakening magnetic behavior and reducing carrier concentration in a phenomenological manner. The resulting theory is found to provide a good agreement with the observed value of T c .

Research paper thumbnail of Magnetic field dependence of the critical current and the flux pinning mechanism in YBa2Cu3O6+x films doped with BaZrO3

Research paper thumbnail of Effects of nanocrystalline target and columnar defects on flux pinning in pure and BaZrO3-doped YBa2Cu3O6+x films in fields up to 30T

Research paper thumbnail of Dependence of critical current density on crystalline direction in thin YBCO films

Physica C: Superconductivity, 2005

ABSTRACT The dependence of critical current density (Jc) on the angle between the current directi... more ABSTRACT The dependence of critical current density (Jc) on the angle between the current direction and the (1 0 0) direction in the ab-plane of thin YBCO films deposited on (0 0 1)-SrTiO3 from nanocrystalline and microcrystalline targets is studied using magneto-optical microscopy. In the films made from the nanocrystalline target it is found that Jc does not depend on the angle whereas Jc decreases with increasing angle in the films made from the microcrystalline target. The films were characterized by detailed X-ray diffraction measurements. The findings are explained in terms of a network of planar defects indicating that in addition to linear defects also the twin boundaries are very important flux pinning sites.

Research paper thumbnail of High pinning potential in YBCO thin films deposited from a target prepared from YBCO nanopowder

Physica C: Superconductivity, 2004

ABSTRACT Thin YBa2Cu3O6+x (YBCO) films were prepared on SrTiO3 substrates by pulsed laser deposit... more ABSTRACT Thin YBa2Cu3O6+x (YBCO) films were prepared on SrTiO3 substrates by pulsed laser deposition using a target made from nanosized powder. These films show high critical current densities Jc≈1×107 A/cm2 at 77 K in zero field as obtained by SQUID magnetization measurements. The pinning potentials, U(T), were calculated from the magnetic relaxation curves measured at several temperatures after cooling the sample in 1 T. From these data the U(0 K) was extrapolated to be 900 K, which is higher than previously reported for as-prepared films.

Research paper thumbnail of Anisotropic pinning defects in BaZrO3-doped YBa2Cu3O6+x films in high magnetic fields

Physica C: Superconductivity, 2008

Angular dependence of the resistivity, the irreversibility field and the critical current of undo... more Angular dependence of the resistivity, the irreversibility field and the critical current of undoped and BaZrO3-(BZO)-doped YBa2Cu3O6+x (YBCO) thin films are investigated using pulsed magnetic fields up to 30T. Doping with BZO forms a dense network of anisotropic c-axis oriented columnar defects, which lead, in comparison with undoped material, to clearly improved values of the pinning potential, the critical current

Research paper thumbnail of Improvement of superconducting properties of old Y–Ba–Cu–O specimens by high-energy heavy ion irradiation

Physica C: Superconductivity, 2006

ABSTRACT Superconducting parameters of different, almost 20 years old Y–Ba–Cu–O samples, prepared... more ABSTRACT Superconducting parameters of different, almost 20 years old Y–Ba–Cu–O samples, prepared in 1987–1988 are investigated. The aim of this research is to find out how a heavy ion beam can enhance the superconducting features of very old and originally not always perfect Y-based specimens. As is observed, their electrical and magnetic characteristics are very sensitive to high-energy Bi-ion irradiation, which results in significant increase of the superconducting parameters. The most important one of them is the global critical current density which is calculated with the help of a new method on the basis of experiments. It can be increased by 18–39%, depending on the original, starting conditions of the samples before the irradiation. At the same time, the average values of intragrain critical current density grows by 37–51%. A slight increase in the critical temperature of 1–2 K was also observed. The experiments on AC susceptibility demonstrate that this irradiation causes to develop faster the total diamagnetic state and decreases the loss. The reason of these effects can be found in the better orientation of crystals, enlargement of microcrystalline aggregates, higher homogenization of the material, thus, in the increase of the superconducting component of samples due to the irradiation.

Research paper thumbnail of Anomalous lattice expansion of RuSr2Eu1.5Ce0.5Cu2O10−δ (Ru-1222) magneto superconductor: A low temperature X-ray diffraction study

Physica C: Superconductivity, 2006

Detailed X-ray diffraction studies on RuSr 2 Eu 1.5 Ce 0.5 Cu 2 O 10-δ (Eu-Ru-1222) magneto super... more Detailed X-ray diffraction studies on RuSr 2 Eu 1.5 Ce 0.5 Cu 2 O 10-δ (Eu-Ru-1222) magneto superconductor down to 13 K at close temperature intervals revealed that with decreasing temperature, the c-parameter decreases linearly down to 100 K, following the relation c = 28.412(1) + 2.5(1)x10 -4 T and then becomes almost temperature independent on further lowering of temperature. Interestingly, the linear decrease in the a-parameter is seen only up to 180 K. Below 180 K, the observed values of the a-parameters are more than the value expected from the linear variation. This departure can be considered as development of strain in the 2 system. Interestingly enough, these temperatures coincide with the complex magnetic ordering (T mag ) of Ru in Ru-1222 system. This is the first report of the observation of the onset of excess volume and also of the strain along the a-axis near the magnetic ordering temperature in Ru-1222 superconductor, and indicates a coupling between the lattice and the magnetism in this system. Magnetization, magneto transport and thermoelectric power measurements being carried out on the same sample are also reported. The results of low temperature excess volume and the strain along a -axis of Ru-1222 compound are reportedly not seen in Ru-1212 (RuSr 2 GdCu 2 O 8 ).

Research paper thumbnail of Magnetism, upper critical field and thermoelectric power of the magnetosuperconductor RuSr 2 Eu 1.5 Ce 0.5 Cu 2 O 10−δ

Journal of Physics: Condensed Matter, 2006

Magnetic susceptibility, M-H plot, magnetoresistance and thermoelectric power of the RuSr 2 Eu 1.... more Magnetic susceptibility, M-H plot, magnetoresistance and thermoelectric power of the RuSr 2 Eu 1.5 Ce 0.5 Cu 2 O 10-δ superconductor are measured. Values of the magnetic transition temperature T mag , superconductivity transition temperature T c , upper critical field H c2 , chemical potential µ, and energy width for electric conduction W σ are obtained from these measurements. It has been found that T mag = 140 K, T c = 25 K (33 K) from susceptibility (magnetoresistance) measurements, H c2 (0) > 32 T, µ = 8 meV, and W σ = 58.5 meV. These values are compared with other ruthenate superconductors, and resulting physical information is discussed.

Research paper thumbnail of Superconducting Properties of Films Deposited From Micro-, Nanocrystalline and Optimally BZO-Doped YBCO Targets

IEEE Transactions on Applied Superconductivity, 2000

Thin YBa2Cu3O6+x (YBCO) films are prepared by pulsed laser deposition (PLD) from pure micro- (mu)... more Thin YBa2Cu3O6+x (YBCO) films are prepared by pulsed laser deposition (PLD) from pure micro- (mu) and nanocrystalline (n) targets and a n-target optimally doped with 3.9 wt% BaZrO3 (BZO). Effects of target grain size and doping on superconducting (SC) properties of the films are investigated using a SQUID magnetometer up to 5 T and transport measurements in pulsed magnetic fiefds

Research paper thumbnail of YBCO Films Prepared by PLD Using Nanocrystalline Targets Doped With<tex>$hboxBaZrO_3$</tex>or Y211

IEEE Transactions on Appiled Superconductivity, 2005

YBCO thin films were prepared by pulsed laser deposition from a pure nanocrystalline YBCO target ... more YBCO thin films were prepared by pulsed laser deposition from a pure nanocrystalline YBCO target and similar targets doped with BaZrO3 or Y2BaCuO5 (Y211 phase) in order to investigate the effect of these impurities on magnetic flux pinning. The doped targets were pressed from nanopowders prepared by a sol-gel method from starting solutions whose nominal molar ratios corresponded to compositions

Research paper thumbnail of Structural Properties of YBCO Thin Films Deposited From Different Kinds of Targets

IEEE Transactions on Applied Superconductivity, 2000

The accommodation field of YBa2Cu3O6+infin (YBCO) a thin films depends on the microstructure of t... more The accommodation field of YBa2Cu3O6+infin (YBCO) a thin films depends on the microstructure of the films and specifically the amount of pinning sites, which can be controlled by the type of the target used in the laser deposition. Typical values for the accommodation field at 5 K are 40-100 mT, 160 mT and 500 mT for films deposited from a

Research paper thumbnail of Curcumin Associated Poly (Allylamine Hydrochloride)-Phosphate Self-Assembled Hierarchically Ordered Nanocapsules: Size Dependent Investigation on Release and DPPH Scavenging Activity of Curcumin

RSC Adv., 2015

Combination of a cationic polyamine with a multivalent anionic salt results in the spontaneous ge... more Combination of a cationic polyamine with a multivalent anionic salt results in the spontaneous generation of ionically crosslinked capsules. Here we report curcumin associated poly(allylamine hydrochloride) crosslinks with dipotassium phosphate and subsequently congregates with silica nanoparticles to form hierarchically ordered nanocapsule structures. The capsule sizes vary depending on the concentration of dipotassium phosphate. SEM data ascertain the spherical shape of the nanocapsules and TEM analysis demonstrates that the outer layer made up of silica has a thickness of $50-250 nm. The fluorescence images confirm that curcumin are present all over the capsules. Strong interaction between nanocapsules and curcumin is evident from spectroscopic analysis and TGA data. Release of curcumin from the nanocapsules is found to be triggered by pH where basic environment trigger the maximum release compared to acidic and neutral conditions. The drug release profile of curcumin from the nanocapsules follows the Higuchi model and depends on the size of the nanocapsules. 2,2-Diphenyl-1picrylhydrazyl (DPPH) scavenging activity of the encapsulated curcumin decreases exponentially with a decrease in size of the nanocapsules, suggesting not only weight percentage of curcumin in the nanocapsules plays a role but also availability of b-diketone group of curcumin for H-donation is vital.