P.K. Sajith

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 .

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.

Development and characterisation of dysprosium barium niobate: a new substrate for YBa2Cu3O7−δ and (Bi,Pb)2Sr2Ca2Cu3Ox superconductor films

Abstract Dysprosium barium niobate has been developed as a new substrate suitable for both YBa 2 Cu 3 O 7− δ (YBCO) and (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O x [Bi(2223)] superconductor films. DyBa 2 NbO 6 (DBNO) has a cubic perovskite (A 2 BB′O 6 ) structure with a lattice constant a =8.456 A. DBNO was found to have a thermal expansion coefficient of 7.806×10 −6 °C −1 and a thermal conductivity of 67.9 W m −1 K −1 . The dielectric constant and loss factor values of DBNO are also in a range suitable for its use as substrate for microwave applications. Both YBCO and Bi(2223) superconductors did not show any detectable chemical reaction with DBNO even under extreme processing conditions. Dip-coated YBCO thick film on polycrystalline DBNO substrate gave a T c (0) of 92 K and J c of ∼1.1×10 4 A cm −2 . Bi(2223) thick film dip-coated on DBNO gave T c (0) of 110 K and J c of ∼4×10 3 A cm −2 .

Epitaxial YBa2Cu3O7−δ—Ag thin films (Jc = 6 × 106 A/cm2) on epitaxial films of Ba2LaNbO6, a new perovskite substrate, by pulsed laser ablation

Abstract Ba2LaNbO6, a new perovskite ceramic substrate material for YBa2Cu3O7−δ has been grown epitaxially on (100) LaAlO3 from a sintered Ba2LaNbO6 pellet by pulsed laser ablation. The optimum substrate temperature for the epitaxial growth of Ba2LaNbO6 on LaAlO3 was found to be 780°C for a laser energy density of 2.6 J/cm2. The epitaxial nature of the Ba2LaNbO6 film was confirmed by X-ray diffraction and AFM studies. A superconducting YBa2Cu3O7−δ—Ag film grown in situ on epitaxial Ba2LaNbO6 film gave Tc(0) = 90 K with a sharp transition of ΔT = 0.4 K. The YBa2Cu3O7−δ—Ag films exhibited excellent (00l) orientation of an orthorhombic YBa2Cu3O7−δ phase and showed almost perfect metallic behaviour in the normal state with resistance ratio ( R 300 K R 100 K ) = 2.95 . Critical current density of 6 × 106 A/cm2 at 77 K was consistently obtained for the YBa2Cu3O7−δ—Ag films deposited on epitaxial Ba2LaNbO6 films. The implications are discussed.

Growth of YBCO–Ag thin films (Tc(0)=90 K) by pulsed laser ablation on polycrystalline Ba2EuNbO6; A new perovskite ceramic substrate for YBCO films

Abstract The development and characterization of a new substrate material Ba2EuNbO6 for YBCO films are reported. Ba2EuNbO6 has a complex cubic perovskite structure [A2(BB′)O6] with a lattice constant a=8.455 A. The dielectric constant and loss factor of this material are in a range suitable for its use as a substrate material for microwave applications. Superconducting YBCO–Ag thin films have been grown in situ on polycrystalline Ba2EuNbO6 by pulsed laser ablation technique and the optimum growth conditions have been established. The films exhibited (00l) orientation of a YBCO orthorhombic phase and gave a zero resistivity superconducting transition at Tc(0)=90 K with a transition width of 1.5 K.

Percolation Behavior of the Normal-State Resistivity and Superconductivity of the YBa2Cu3O7−δ-Ba2GdNbO6 Composite System

The percolation behavior of the normal-state resistivity and superconductivity of the YBa2Cu3O7−δBa2GdNbO6 composite system were studied by X-ray diffraction and temperature-resistivity measurements. No detectable chemical reaction was observed between the YBa2Cu3O7−δ superconductor and the ceramic insulator Ba2GdNbO6, even after severe heat treatment above 950°C. The normal-state and superconducting percolation threshold values were found to be 17 vol.% and 30 vol.% of YBa2Cu3O7−δ respectively in the YBa2Cu3O7−δ-Ba2GdNbO6 composite system. The values obtained for the critical exponents describing the normal-state pecolation behavior of the system matched fairly well with the theoretically expected values for an ideal metal-insulator composite system.

Superconducting YBa 2Cu 3O 7-δ -Ag Thin Films (TC( 0) = 90 K) by Pulsed Laser Deposition on Polycrystalline Ba 2NdNbO 6; A Novel Substrate for YBa 2Cu 3O 7-δ Films

The development and characterisation of \ba, a novel ceramic substrate material for \yb superconductor, are reported. \ba has a complex cubic perovskite structure [\bb] with lattice constant a = 8.573A. The dielectric properties of \ba are in a range suitable for its use as a substrate for microwave applications. \ba was found to have a thermal expansion coefficient of 8.6×10-6 °C-1 and a thermal conductivity of 87 Wm-1K-1. Superconducting \yb-Ag thin films have been grown in situ on polycrystalline \ba by pulsed laser ablation technique and the optimum conditions have been established. The films exhibited (00l) orientation of an orthorhombic \yb phase and gave a zero resistivity superconducting transition [TC(0)] at 90 K with a transition width of ~1.5 K and JC ~3 ×105 A/cm2 at 77 K.

a new perovskite ceramic substrate for YBCO and Bi(2223) superconductor films

A new ceramic material has been synthesized and sintered as single-phase material for use as a substrate for both and superconductors. has a complex cubic perovskite structure , with a lattice constant a = 8.462 A. The dielectric constant and loss factor are in a range suitable for its use as a substrate for microwave applications. YBCO and Bi(2223) superconductors did not show any detectable chemical reactivity (within the precision of the x-ray diffraction technique) with , even under severe heat treatment. The dip-coated thick films of YBCO on polycrystalline substrate gave a of 92 K and a critical current density of at 77 K. A dip-coated Bi(2223) thick film on substrate gave a of 110 K and a current density at 77 K.

Superconducting YBCO-Ag (Tc(0) = 92 K) and Bi(2223)-Ag (Tc(0) = 110 K) composite thick films by dip coating on DyBa2SnO5.5, a new perovskite ceramic substrate

Abstract Superconducting YBCO-Ag and Bi(2223)-Ag composite thick films have been fabricated on polycrystalline DyBa 2 SnO 5.5 , a new cubic perovskite substrate, by dip coating. The thick films of YBCO-Ag dip coated on polycrystalline DyBa 2 SnO 5.5 substrate gave to a T c(0) = 92 K and a critical current density ( J c ) ≃ 7 × 10 4 A/cm 2 at 77 K for 6 vol.% of Ag in the composite. A dip-coated Bi(2223)-Ag composite thick film on DyBa 2 SnO 5.5 gave a T c(0) = 110 K and critical current density ∼1 × 10 4 A/cm 2 at 77 K for an addition of 6 vol.% of Ag in the composite. The effect of Ag volume fraction on the critical current density and orientation in YBCO-Ag and Bi(2223)-Ag composite thick films have also been discussed.