J. Kurian

Electrical transport and superconductivity in YBa2Cu3O7−δ ‐YBa2HfO5.5 percolation system

Percolation behavior of the normal state resistivity and superconductivity of YBa2Cu3O7−δ‐YBa2HfO5.5 composites has been studied by x‐ray diffraction and temperature‐ resistivity measurements. No detectable chemical reactivity was observed between YBa2Cu3O7−δ and a ceramic insulator YBa2HfO5.5 even when the two materials were mixed thoroughly and sintered at 1020 °C. Normal state and superconducting percolation threshold values are ≊23 vol % of YBa2Cu3O7−δ in the composite. The values obtained for the critical exponents describing the normal state transport behavior of the system matched with theoretically expected values for an ideal conductor‐insulator percolation system. The implications are discussed.

Novel ceramic substrates for high Tc superconductors

A group of complex perovskite oxides REBa2NbO6 (RE=La and Dy) have been synthesized and developed for their use as substrates for both YBa2Cu3O7-δ and Bi(2223) superconductors. These materials have a complex cubic perovskite (A2BB′O6) structure with lattice constants,a=8·48−8·60 Å. REBa2NbO6 did not show any phase transition in the temperature range 30–1300°C. The thermal expansion coefficient, thermal diffusivity and thermal conductivity values of REBa2NbO6 are favourable for their use as substrates for highTc superconductors. The dielectric constant and loss factor of REBa2NbO6 are in a range suitable for their use as substrates for microwave applications. Both YBa2Cu3O7-δ and Bi(2223) superconductors did not show any detectable chemical reaction with REBa2NbO6 even under extreme processing conditions. Dip coated YBa2Cu3O7-δ thick films on polycrystalline REBa2NbO6 substrate gave aTc(0) of 92 K and a current density of ∼1·1×104 A/cm2 and Bi(2223) thick film on polycrystalline REBa2NbO6 substrate gave aTc(0) of 110 K and a current density of ∼ 4×103 A/cm2 at 77 K and zero magnetic field. A laser ablated YBa2Cu3O7-δ thin film deposited on polycrystalline REBa2NbO6 substrate gave aTc(0) of 90 K and a current density of ∼5×105 A/cm2.

REBa 2 ZrO 5.5 (RE = La, Ce, Eu, and Yb): Synthesis, characterization, and their potential use as substrates for YBa 2 Cu 3 O 7–δ superconductors

A new class of complex perovskites REBa 2 ZrO 5.5 (where RE = La, Ce, Eu, and Yb) have been synthesized and sintered as single phase materials by the solid state reaction method. The structure of these materials was studied by x-ray diffraction, and all of them were found to be isostructural, having a cubic perovskite structure. X-ray diffraction and resistivity measurements have shown that there is no detectable chemical reaction between YBa 2 Cu 3 O 7–delta; and REBa 2 ZrO 5.5 even under severe heat treatment at 950 °C, and that the addition of REBa 2 ZrO 5.5 up to 20 vol.% in YBa 2 Cu 3 O 7–δ shows no detrimental effect on the superconducting properties of YBa 2 Cu 3 O 7-δ . Dielectric constants and loss factors are in the range suitable for their use as substrates for microwave applications. Thick films of YBa 2 Cu 3 O 7–δ fabricated on polycrystalline REBa 2 Zr O5.5 substrates gave a zero resistance transition temperature T c (0) ∼ 92 K, indicating the suitability of these materials as substrates for YBa 2 Cu 3 O 7–δ .

YBa2HfO5.5: a new perovskite potentially suitable as a substrate for YBCO films

Abstract Addition of HfO 2 to YBa 2 Cu 3 O 7−δ resulted in the formation of a second phase during high-temperature annealing at 950°C. This second phase was identified as YBa 2 HfO 5.5 , a new compound having a perovskite cubic structure with lattice constant a = 8.372 A . YBa 2 HfO 5.5 was synthesized for the first time as a single-phase material by solid-state reaction. It has been found that superconducting YBa 2 Cu 3 O 7−δ does not react with YBa 2 HfO 5.5 even after heating a 1:1 molar mixture at 950°C for 15 h. Dielectric constant and loss factor of this material, studied in the frequency range 30 Hz to 13 MHz, were found to be in the range suitable for possible use as a substrate for YBa 2 Cu 3 O 7−δ films for microwave applications.

Barium rare-earth zirconates : synthesis, characterisation and their possible application as substrates for YBa2Cu3O7−δ superconductors

A new class of complex perovskite oxides Ba{sub 2}REZrO{sub 6{minus}x} (RE = Pr, Nd, Sm and Gd) have been synthesized and sintered as single phase materials with high sintered density and stability by solid state reaction method. The structure of Ba{sub 2}REZrO{sub 6{minus}x} was studied by X-ray diffraction technique and all of them were found to be isostructural and have a cubic perovskite structure. No chemical reaction was observed between Ba{sub 2}REZrO{sub 6{minus}x} and YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} even after annealing a 1:1 volume mixture at 950 C for 20 h. The dielectric constant and loss factor of these materials are in a range suitable for their use as substrates for YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} superconductors. Ba{sub 2}REZrO{sub 6{minus}x} melts congruently and could be grown as single crystals from melt.

Growth of YBa2Cu3O7−δ–Ag thin films (Tc(0)=89 K) by pulsed laser ablation on polycrystalline Ba2LaNbO6: A new perovskite ceramic substrate

Synthesis and characterization of Ba{sub 2}LaNbO{sub 6} which is a new substrate material for YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} superconductor are reported. Ba{sub 2}LaNbO{sub 6} has a complex cubic perovskite structure (A{sub 2}BB{prime}O{sub 6}) with a lattice constant {ital a}=8.60 A. No detectable chemical reaction between YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} and Ba{sub 2}LaNbO{sub 6} was observed even under severe heat treatment. The dielectric constant and loss factor of Ba{sub 2}LaNbO{sub 6} are in a range suitable for its use as a substrate for microwave applications. Superconducting YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}{endash}Ag thin films are grown {ital in} {ital situ} on polycrystalline Ba{sub 2}LaNbO{sub 6} by pulsed laser ablation method. The film exhibited (00{ital l}) orientation of an orthorhombic YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} phase. The films gave a {ital T}{sub {ital c}} onset of 91 K and {ital T}{sub {ital c}(0)} of 89 K. {copyright} {ital 1996 American Institute of Physics.}Synthesis and characterization of Ba2LaNbO6 which is a new substrate material for YBa2Cu3O7−δ superconductor are reported. Ba2LaNbO6 has a complex cubic perovskite structure (A2BB′O6) with a lattice constant a=8.60 A. No detectable chemical reaction between YBa2Cu3O7−δ and Ba2LaNbO6 was observed even under severe heat treatment. The dielectric constant and loss factor of Ba2LaNbO6 are in a range suitable for its use as a substrate for microwave applications. Superconducting YBa2Cu3O7−δ–Ag thin films are grown in situ on polycrystalline Ba2LaNbO6 by pulsed laser ablation method. The film exhibited (00l) orientation of an orthorhombic YBa2Cu3O7−δ phase. The films gave a Tc onset of 91 K and Tc(0) of 89 K.

YBa2SnO5·5, a novel ceramic substrate for YBCO and BiSCCO superconductors

YBa2SnO5·5 has been synthesized and sintered as single phase material for its use as substrate for both YBCO and BiSCCO superconductors. YBa2SnO5·5 has a complex cubic perovskite (A2BB’O6) structure with the lattice constanta = 8·430 Å. The dielectric constant and loss factor of YBa2SnO5·5 are in a range suitable for its use as substrate for microwave applications. YBa2SnO5·5 is found to be chemically compatible with both YBCO and BiSCCO superconductors. The thick film of YBCO screen printed on polycrystalline YBa2SnO5·5 substrate gave aTc(0) of 92 K and a critical current density (Jc) of 4 × 104 A/cm2 at 77 K. A screen printed BiSCCO thick film on YBa2SnO5·5 substrate gaveTc(0) = 110 K and current density 3 × 103 A/cm2 at 77 K.

Superconducting YBa2Cu3O7−δ thick film (Tc(0) = 92 K) on SmBa2NbO6: a newly developed perovskite ceramic substrate☆

A complex perovskite oxide, YbBa2NbO6, as a non-reacting substrate for YBa2Cu3O7-° super-conducting film has been developed. The dielectric constant and loss factor values of the material are in the range suitable for its use as substrate for microwave applications. A YBa2Cu3O7−δ superconducting thick film dip coated on YbBa2NbO6 substrate gave a Tc (0) of 92 K and current density of ∼ 1.3 × 104 A cm−2.

Development and characterization of GdBa2NbO6, a new ceramic substrate for YBCO thick films

Abstract The development and characterization of a new substrate material GdBa 2 NbO 6 , having moderately low dielectric constant and loss factor at MHz frequencies are reported. It has been found that superconducting YBa 2 Cu 3 O 7−δ does not react with Gd-Ba 2 NbO 6 even after a 1:1 volume mixture was heated at 950°C for 15 h. The suitability of GdBa 2 NbO 6 as a substrate for YBa 2 Cu 3 O 7−δ thick films was confirmed by fabricating a thick film of YBa 2 Cu 3 O 7−δ on this substrate by screen printing which gave a zero-resistivity superconducting transition at T c (0) = 92 K with a transition width of 2 K.

The structural and superconducting properties of the YBa2Cu3O7−δ‐HfO2 system

Superconductivity in YBa2Cu3O7−δ with HfO2 addition has been studied by x‐ray diffraction, temperature‐resistivity measurements, and scanning electron microscopy. The studies revealed that HfO2 addition up to 5 wt % does not have any detrimental effect on the superconducting properties of YBa2Cu3O7−δ. It is also found that the widely accepted procedure of slow cooling or prolonged heating at 600 °C for oxygenation of the samples is not essential to obtain superconductivity in an HfO2‐added YBa2Cu3O7−δ system. A superconducting transition (92 K) was obtained by directly quenching the HfO2‐added samples in air from a sintering temperature of 950 °C. A tetragonal to orthorhombic transformation has taken place within seconds, indicating that the rate of oxygen absorption has increased tremendously by HfO2 addition. The implications are discussed.