Asha M. John

A new combustion process for nanosized YBa2ZrO5.5 powders

Abstract A new single step process for the synthesis of nanoparticles of YBa 2 ZrO 5.5 , a complex perovskite ceramic oxide, is reported for the first time. In the present modified combustion method no calcination step was needed to obtain phase pure powder of YBa 2 ZrO 5.5 . The YBa 2 ZrO 5.5 powder, obtained by self sustained combustion of a precursor complex of the respective metal ions, is characterised by High Resolution Transmission Electron Microscopy, Powder X-ray Diffraction, Differential Thermal Analysis, Thermo-gravimetric Analysis, FT-IR Spectroscopy, BET surface area Analysis and Agglomerate size analysis. The particle size of the as prepared YBa 2 ZrO 5.5 was in the range 5 nm to 50 nm. The lattice image of the nanocrystalline particle showed very little distortion and the intercrystalline boundary was quite sharp without any second phase.

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 .

Synthesis of Nanosized Ba2LaZrO5.5 Ceramic Powders through a Novel Combustion Route

A single-step process for the preparation of nanoparticles of Ba2LaZrO5.5 is reported in this paper. The process is a modification of the combustion method, which resulted in Ba2LaZrO5.5 phase without a calcination step. This complex perovskite ceramic oxide thus obtained is characterized by high-resolution transmission-electron microscopy, X-ray and electron diffraction, thermal analysis, FT-IR spectroscopy, surface area measurements, and particle-size analysis. The particle size of Ba2LaZrO5.5 was in the range 10–70 nm and were of regular shape with well-defined grain boundaries.

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.

Synthesis and characterization of nanoparticles of Ba2EuHfO5.5: a new complex perovskite ceramic oxide

Abstract Ba 2 EuHfO 5.5 , a complex perovskite oxide, has been synthesized as nanoparticles using a modified self-propagating combustion method for the first time. The Ba, Eu and Hf ions required for the formation of Ba 2 EuHfO 5.5 were obtained in solution by dissolving a stoichiometric mixture of BaCO 3 , Eu 2 O 3 and HfO 2 heated at 1200°C for 4 h in boiling nitric acid. By complexing the ions with citric acid and using ammonia as fuel, it was possible to get Ba 2 EuHfO 5.5 as nanoparticles in a single step combustion process. The solid combustion product was characterized using X-ray powder diffraction, thermogravimetric analysis, differential thermal analysis, infrared spectroscopy, surface area analysis and high resolution transmission electron microscopy. The high resolution transmission electron microscopic examination of the product showed an average particle size of about 25 nm with a standard deviation of 13 nm. The nanoparticles of Ba 2 EuHfO 5.5 synthesized by the combustion technique could be sintered to >97% of the theoretical density at a relatively low temperature.

Synthesis and Rapid Densification of Nanoparticles of Barium Praseodymium Hafnium Oxide: A New Complex Perovskite

Nanoparticles (25–100 nm) of barium praseodymium hafnate (Ba2PrHfO5.5), a new substrate material for high temperature superconducting YBa2Cu3O7-δ and Bi-cuprate films has been synthesized through an exothermic chemical reaction for the first time. The Ba, Hf and Pr ions required for the formation of Ba2PrHfO5.5 were obtained in solution by dissolving a stoichiometric mixture of BaCO3, Pr6O11 and HfO2 heated at 1200°C for 4 h in boiling nitric acid. By complexing the ions with citric acid and adjusting the oxidant/fuel ratio, it was possible to obtain Ba2PrHfO5.5 as nanoparticles in a single step chemical process. The nanoparticles thus obtained were characterized by powder X-ray diffraction, thermogravimetric analysis, differential thermal analysis, infrared spectroscopy, and surface area analysis. The Ba2PrHfO5.5 synthesized through the present exothermic chemical process, because of its nanoparticulate nature, could be sintered to a density of 98% in a period of just 9 min at a temperature of 1435°C in air. Scanning electron microscopic studies on the sintered Ba2PrHfO5.5 samples showed that densification has occurred without significant microstructural coarsening up to a sintered density of 98% of its theoretical value in a short duration.

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.

Superconducting Bi(2223) films (TC(0)=110 K) by dip-coating on Ba2LaZrO5.5: a newly developed perovskite ceramic substrate

Abstract Ba 2 LaZrO 5.5 has been developed as a new ceramic substrate suitable for Bi(2223) superconductor films. Ba 2 LaZrO 5.5 has a complex cubic perovskite (A 2 BB′O 6 ) structure with a lattice constant a =8.395 A. The dielectric constant and loss factor of Ba 2 LaZrO 5.5 are in a range suitable for its use as a substrate material for microwave applications. Bi(2223) superconductor does not show any detectable chemical reaction with Ba 2 LaZrO 5.5 even under extreme processing conditions. The thick films of Bi(2223) dip-coated on polycrystalline Ba 2 LaZrO 5.5 substrate gave a T C (0) of 110 K and a current density of ∼4×10 3 A/cm 2 at 77 K and zero magnetic field. The Bi(2223) films exhibited excellent adhesion to Ba 2 LaZrO 5.5 . Dip coating was found to be one of the easiest methods for obtaining superconducting Bi(2223) thick film of thickness as low as ∼4 μm.

A comparative study on in situ grown superconducting YBCO and YBCO-Ag thin films by PLD on polycrystalline SmBa2NbO6 substrate

The development and characterization of SmBa2NbO6, which is a new ceramic substrate material for the YBa2Cu3O7- superconductor, are reported. SmBa2NbO6 has a complex cubic perovskite structure with lattice constant a = 8.524 A. The dielectric properties of SmBa2NbO6 are in a range suitable for its use as a substrate for microwave applications. SmBa2NbO6 was found to have a thermal conductivity of 77 W m-1 K-1 and a thermal expansion coefficient of 7.8 × 10-6 °C-1 at room temperature. Superconducting YBa2 Cu3O7- and YBa2Cu3O7- -Ag thin films have been grown in situ on polycrystalline SmBa2NbO6 by the pulsed laser ablation technique. The films exhibited (00l) orientation of an orthorhombic YBa2 Cu3O7- phase and gave a zero resistivity superconducting transition (TC(0)) at 90 K with a transition width of ~1.5 K. The critical current density of YBCO-Ag thin films grown on polycrystalline SmBa2NbO6 substrate was ~3 × 105 A cm-2 at 77 K. A comparative study of YBCO and YBCO-Ag thin films developed on polycrystalline SmBa2NbO6 substrate by PLD based on the crystallinity, orientation and critical current density of the YBCO film is discussed in detail.