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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 41 (1999), S. 355-361 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied the growth characteristics, structure, and parameters of the epitaxial heterostructures (001)NdBa2Cu3O7−δ /(100)SrTiO3/(001)NdBa2Cu3O7−δ grown by laser ablation on a (100)LaAlO3 substrate with a thin (∼2 nm) YBa2Cu3O7−δ intermediate layer. The use of an YBa2Cu3O7−δ intermediate layer promotes layered growth of the (200 nm) NdBa2Cu3O7−δ layer, whose free-surface roughness is 4–5 nm. The resistance of the NdBa2Cu3O7−δ layers began to fall off abruptly at T=92 K, and at T≈87 K it vanished completely. The critical current density in the NdBa2Cu3O7−δ layers at T=76 K exceeded 106 cm2 A/cm2. The dielectric constant of the (400 nm) SrTiO3 layer sandwiched between the NdBa2Cu3O7−δ epitaxial layers grew by roughly threefold as the temperature was lowered in the interval 300–4.2 K. When a bias voltage of ±2.5V was applied to the NdBa2Cu3O7−δ electrodes, the relative dielectric constant of the (400 nm) SrTiO3 intermediate layer fell from 1150 to 400 (T=32 K, f=100 kHz). The conductivity of the SrTiO3 intermediate layer in the direction perpendicular to the substrate plane increased with temperature and the electric field strength.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Epitaxial SrBi2Nb2O9 films were grown by laser ablation on (001)YBa2Cu3O7−δ /(100)SrTiO3 and (001)NdGaO3, with c axis normal to the substrate plane. The SrBi2Nb2O9 films were grown in a layer-by-layer regime on NdGaO3 substrates in 25-Å steps at a condensation temperature of 700 °C. Microinclusions of secondary phases and a-oriented grains were observed to exist on the surface of (001)SrBi2Nb2O9 films grown on (001)YBa2Cu3O7−δ /(100)SrTiO3. The dielectric permittivity of the SrBi2Nb2O9 films measured along the c axis is 123 (T=300 K, f=100 kHz), and tan δ≈0.04.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 39 (1997), S. 195-199 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The formation of epitaxial heterostructures including YBa2Cu3O7−δ and SrTiO3 thin films on R-plane sapphire substrates has been studied. The thin CeO2 layer and the CeO2/SrBi2Nb2O9 epitaxial bilayer served as buffers. The temperature dependence of the dielectric permittivity ɛ of the SrTiO3 film behaved in essentially different ways when incorporated in the YBa2Cu3O7−δ /SrTiO3/YBa2Cu3O7−δ and in Ag/SrTiO3/YBa2Cu3O7−δ capacitor structures. An external bias U b=±2.5 V applied to a plane-parallel YBa2Cu3O7−δ /SrTiO3/YBa2Cu3O7−δ capacitor structure (T〈100 K) reduced the ɛ of the SrTiO3 film to one half its original value.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 42 (2000), S. 2103-2108 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Precisely (100)-oriented, 200-nm thick La0.67Ca0.33MnO3 films have been grown by laser ablation on a sapphire (R-plane) substrate covered by a (100)SrTiO3/(001)Bi2SrNb2O9/(001)CeO2 trilayer buffer. The azimuthal misorientation of crystal grains (50–300 nm) in the La0.67Ca0.33MnO3 films decreased by about 40% as the condensation temperature was increased ered from 760 to 810° C. The lattice parameter of the grown manganate films was reduced to 3.81–3.82 Å by enriching them with oxygen. The maximum in the temperature dependence of the electrical resistivity of the La0.67Ca0.33MnO3 films grown was shifted toward lower temperatures by 20–50 K relative to its position for bulk ceramic samples of a stoichiometric composition. The largest magnetoresistance (MR=42% at H=0.4 T) was found in La0.67Ca0.33MnO3 films with a Mn4+ concentration on the order of 50% (T=166 K).
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 39 (1997), S. 1542-1547 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A bi-epitaxial (001)YBa2Cu3O7−δ /(110)BaZrO3/(001)CeO2 three-layer heterostructure has been grown on (100)SrTiO3 by laser ablation. The epitaxial relations between the layers making up the heterostructure were derived from x-ray diffraction data. The I cRn product for the bi-epitaxial Josephson junctions thus obtained was within 1–1.5 mV for 4.2 K, and 30–60 µV for 77 K. The normal resistance R n=(2–5 Ω) was practically independent of temperature. The magnetic field dependences of I c had typically a clearly pronounced main maximum, followed by distorted subsequent peaks. Interaction of the Josephson ac current with self-induced electromagnetic waves at the 45° grain boundary and with external microwave radiation (f=11 GHz) produced current steps in the I-V characteristics of the bi-epitaxial junctions at the corresponding voltages.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 40 (1998), S. 183-186 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract (001)YBa2Cu3O7−δ epitaxial films were prepared by laser ablation on $$(1\bar 102)Al_2 O_3 $$ surface. A thin (001)CeO2 or (111)CeO2 buffer layer was deposited between the substrate and the superconductor film to reduce their chemical interaction. In the initial stages of CeO2 buffer formation, its orientation depended strongly on the intensity of cerium ion interaction with oxygen. Epitaxial growth of (001)YBa2Cu3O7−δ films was achieved both on $$(001)CeO_2 //(1\bar 102)Al_2 O_3 $$ and $$(111)CeO_2 //(1\bar 102)Al_2 O_3 $$ . The T c temperature of epitaxial (001)YBa2Cu3O7−δ films was within 88–90 K, and the current J c at 77 K was in excess of 106 A/cm−2.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4591-4595 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial trilayer heterostructures of YBa2Cu3O7−δ/BaxSr1−xTiO3/YBa2Cu3O7−δ were grown on silicon-on-sapphire buffered by a double layer of CeO2/Y–ZrO2. Such structures may be considered for tunable microwave filters. The top and bottom YBa2Cu3O7−δ films were well c-axis oriented, free from microcracks and had superconducting transitions Tc's in the range 86–90 K. A thin antidiffusion layer of SrTiO3 (d≈70 A(ring)) between YBa2Cu3O7−δ and BaxSr1−xTiO3 (x=0.25–0.9) promoted better crystallinity and higher Tc of the top superconducting film. An Ag/BaxSr1−xTiO3/YBa2Cu3O7−δ capacitor structure was used to determine the dielectric permittivity and the high frequency loss tan δ of the BaxSr1−xTiO3 layer. Maximum values of the permittivity of the BaxSr1−xTiO3 layers were observed around the Curie temperatures of corresponding bulk monocrystals. The dielectric permittivity of the BaxSr1−xTiO3 (x=0.25–0.75) layers depended strongly (≈20%) on an applied voltage (±2.5 V) at temperatures around 77 K. The tan δ was much higher in films than in bulk crystals. © 1995 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 1654-1657 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-current-density Josephson junctions have been produced in high-temperature superconducting YBa2Cu3O7−δ films deposited on silicon on sapphire and using biepitaxial grain boundaries. The technique is estimated to be useful in integrating superconducting and semiconducting components. A multilayer system of epitaxially grown films was used to form the junctions. A double buffer layer CeO2/ZrO2(9.5% Y2O3) prevented interactions between YBa2Cu3O7−δ and Si during the high-temperature deposition and promoted formation microcrack-free films with a critical current density of 2×106 A/cm2 at 77 K. A MgO seed layer, with (001)MgO(parallel)(001)CeO2 orientation, was used to induce a 45° crystallographic grain boundary in YBa2Cu3O7−δ at its edge. An additional epitaxial buffer double layer of YBa2Cu3O7−δ and SrTiO3 on top of the seed layer promoted the formation of a grain boundary of better crystallinity and stoichiometry. It improved the critical current of the junction about tenfold and resulted in characteristic IcRn products of 150 μV at 77 K in microbridges crossing the grain boundary. Microwave-induced steps were detected at 77 K up to voltages corresponding to the characteristic IcRn value. Peak-to-peak responses to superconducting quantum interference devices reached values of 7 μV at 77 K. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 3232-3236 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The combination of a low loss, high-Tc superconductor and a polarizable dielectric looks interesting from the point of tunable, high Q filters for cellular communication. Epitaxial heterostructures of YBa2Cu3O7−∂/SrTiO3/YBa2Cu3O7−∂/CeO2 and SrTiO3/YBa2Cu3O7−∂/CeO2 were grown on sapphire substrates in this study. Superconducting transition temperatures of 88–90 K and a critical current density of about 2×106 A/cm2 at 77 K were determined for YBa2Cu3O7−∂ films on CeO2 buffered sapphire. An effective permittivity of 340 at 300 K was measured capacitively for the SrTiO3 layer between YBa2Cu3O7−∂ electrodes; it increased three times at 50 K. The dielectric constant of SrTiO3 was observed to decrease a factor of 2 as a dc bias voltage of ±2.5 V was applied between the electrodes. Much smaller nonlinearities and temperature dependences of the dielectric constant were noted if the top YBa2Cu3O7−∂ electrode was replaced by an Ag one. © 1997 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 5053-5059 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial films of ferroelectric barium titanate are desirable in a number of applications but their properties are inferior to those of bulk material. Relations between microstructure and dielectric properties may give better understanding of limitations. Trilayer heterostructures SrRuO3/BaTiO3/SrRuO3 were grown by laser ablation on (100)LaAlO3 and (100)MgO substrates. The BaTiO3 layer was granular in structure. When grown on (100)SrRuO3/(100)LaAlO3, it was preferentially a-axis oriented due to tensile mechanical stress. Using (100)MgO as a substrate, on the other hand, produced a mixture of about equal value of a-axis and c-axis oriented grains of BaTiO3. The dielectric permittivity, cursive-epsilon, of the BaTiO3 layer was almost twice as large, at T〉200 K and f=100 kHz, for the LaAlO3 substrate as compared to the MgO one. Its maximum value (cursive-epsilon/cursive-epsilon0(approximate)6200) depended on temperature of growth, grain size, and electric field and compares well with optimal values commonly used for ceramic material. The maximum in the cursive-epsilon(T) shifted from about 370 to 320 K when the grain size in the BaTiO3 film decreased from 100 to 40 nm. At T〈300 K, hysteresis loops in polarization versus electric field were roughly symmetric. The BaTiO3 films grown on (100)SrRuO3/(100)MgO exhibit the largest remnant polarizations and coercive fields in the temperature range 100–380 K. © 2001 American Institute of Physics.
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