Synthesis, processing behavior, and characterization of bismuth superconductors using freeze dried nitrate precursors

Abstract

The synthesis of Bi2−xPbxSr2Ca2Cu3O10 (Bi2223) powders from a freeze dried nitrate precursor is reported here. We examine the composition and morphology of the precursor material, describe the chemistry and kinetics of product formation, and evaluate the phase composition and superconducting properties of the products. A nitrate solution containing the appropriate ratio of cations was rapidly frozen and then freeze dried at low temperatures to form an atomic mixture of the component salts. The thermal processing of the freeze dried material consisted of three steps: (i) dehydration, (ii) denitration, and (iii) solid state reaction to form the Bi2223 superconducting product. Calcium-substituted bismuthates and strontium-substituted calcium cuprate, not Bi2201, are the intermediates between the nitrates and the superconducting products. These highly disordered phases rapidly transform into Bi2212 or Bi2223 at higher temperatures (≍790 °C). The kinetics of product formation was studied using XRD analysis and magnetic susceptibility. The kinetics were shown to follow the nucleation and growth mechanism. Bi2223 formed after only 30 min at a few degrees below the melting point, and after 37 h Bi2223 products exhibited excellent phase composition and magnetic susceptibility characteristics.

BiVO4 as a Visible-Light Photocatalyst Prepared by Ultrasonic Spray Pyrolysis

“…We believe the formation of BiVO 4 particles occurs by a similar mechanism (Scheme ). The thermal decomposition of Bi(NO 3 ) 3 and NH 4 VO 3 results in the evolution of NO x , NH 3 , and H 2 O gas , which, if formed inside a shell of BiVO 4 , could form the blow-outs, pores, and broken shells seen in the final product. In addition, the ball-in-ball type structure is likely the result of remnant precursor decomposition inside the already formed outer shell.…”

One step synthesis of Bi(Pb)-2223 phase in Bi(Pb)-Sr(Ba)-Ca-Cu nitrate freeze dried powder

“…It is important to remove the CO 3 from the powder during the solid-state synthesis because, as shown in [6], the residual C is located preferentially at the grain boundaries and is favourable to the formation of secondary phases and to the decrease of the material's current density j c . To overcome the presence of the carbonaceous anions, for the synthesis of 2223 ceramic, spray freezing of a nitrate aqueous solution followed by freeze drying has been applied by different authors [7][8][9][10][11][12]. In all these papers as well as in our research [12,13], after the nitrate precursor powder was obtained, processing routes were multistep ones.…”

Reactive-field-assisted-sintering of freeze-dried powders in the BSCCO system

“…Previous efforts have been focused on the synthesis of Bi(Pb)-2223-phase using nano-nitrate precursor powder obtained by the spray frozen, freeze-dried technique [2][3][4][5][6][7][8][9][10]. We have recently proposed a new route for the superconducting 2223-phase synthesis of dried powder in non-isothermal 3 Author to whom correspondence should be addressed.…”