Yogendra P. Yadava

Rare-Earth Barium Niobates:* A New Class of Potential Substrates for YBa2Cu3O7-δ Superconductor

A class of complex perovskites REBa2NbO6 (where RE=Pr, Nd, Sm and Eu) have been sintered as single phase materials having a high sintered density and stability, for their use as substrates for YBa2Cu3O7-δ superconductors. The structure of these materials was studied by X-ray diffraction technique and all of them were found to be isostructural having a cubic perovskite structure. These newly developed materials do not react with YBa2Cu3O7-δ superconductors even after annealing 1:1 volume mixture at 950° C for 15 h. The presence of REBa2NbO6 upto 20 vol% in the YBa2Cu3O7-δ–REBa2NbO6 composite did not show any deterimental effect on the superconducting transition temperature of YBa2Cu3O7-δ. Dielectric constant and loss factor of REBa2NbO6 were found to be in the range suitable for their use as substrates for microwave applications. Superconducting YBa2Cu3O7-δ thick films screen-printed on these new substrates gave a zero transition temperature T c0≈92 K and current density≈2×105 A/cm2 at 77 K.

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.

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.

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.

Superconducting Bi‐cuprate thick film Tc(0)=110 K on DyBa2SnO5.5: A newly developed perovskite substrate

A new ceramic perovskite DyBa2SnO5.5 has been synthesized and developed for its use as a substrate for Bi(Pb)–Sr–Ca–CuO superconductors. The dielectric constant and loss factor of this material are in a range suitable for its use as a substrate for microwave applications. DyBa2SnO5.5 is found to be chemically compatible with Bi(Pb)–Sr–Ca–CuO superconductors. Bi(2223) superconducting thick film fabricated on DyBa2SnO5.5 substrate gave a Tc(0)=110 K with a transition width of 2 K.

Growth of YBCO thin films (Tc(O) = 90 K) by pulsed laser ablation on polycrystalline GdBa2NbO6 , a new perovskite ceramic substrate

Abstract Superconducting YBCO thin films are grown in situ on polycrystalline GdBa2NbO6, a new cubic perovskite substrate by the pulsed laser ablation method and the optimum growth conditions have been established. The films exhibited (001) orientation of a YBCO orthorhombic phase. The films gave a Tc (onset) of 92 K and Tc(O) of 90 K.