An enhancement in structural and superconducting properties of Bi2212 epitaxial thin films grown by the Pechini sol–gel method

Abstract

Bi2Sr2CaCu2O8+δ (Bi2212) superconducting thin films were prepared by the Pechini sol–gel method using nitrates as reactants. The precursor sol was deposited on SrTiO3(001) single‐crystal substrates via the spin‐coating method, and the results revealed the lowering of the Bi2212 phase‐transition temperature; meanwhile the sintering time was significantly reduced. According to this investigation, the phase purity and crystallinity of Bi2212 thin films were obviously improved owing to the stable gel mechanism; the Tc,onset transition temperature value of the pure c‐axis Bi2212 thin films rose to about 95 K.

Crystalline characteristics and superconducting properties of Bi2212 thin films prepared by the Pechini sol–gel method: the effect of different substrates on the film growth

“…values of group L range from 22 to 28 nm. The surface particle sizes of samples M1, M2 and M4 are obviously larger than those of group L. The calculated surface roughness values of group M range from 56 to 79 nm, and thus obviously they are larger than those of group L and those of a similar set of samples (denoted group F in previous work; Lu et al, 2013) Tables 1 and 2, respectively. According to the Stranski-Krastanov mode, the transition from layer-by-layer to island-based growth occurs at a critical layer thickness, at which the strain energy induced by the lattice mismatch between film and substrate is relaxed (Eaglesham et al, 1991).…”

“…Analytical reagents Bi(NO 3 ) 3 Á5H 2 O, Sr(NO 3 ) 2 , Ca(NO 3 ) 2 Á 4H 2 O and Cu(NO 3 ) 2 Á3H 2 O were used as reactants in the molar ratio of Bi:Sr:Ca:Cu = 2:2:1:2, while ethylenediaminetetraacetic acid (EDTA, the molar ratio of EDTA to metal ions was 1:1) and ethylene glycol were, respectively, used as chelating and polymerizing agent to prepare the blue precursor solution. The experimental process has been described in detail elsewhere (Lu et al, 2013).…”

“…In the first step, the precursor gels were decomposed by heating from room temperature to 873 K (T p ) at 2 K min À1 and maintained for 60 min (t p ) in air. Details of the analysis of precursor films have been reported in our previous work (Lu et al, 2013). Secondly, the precursor films were heated from 873 K to 1090-1100 K (T s ) at a rate of 3.5 K min À1 , held at this temperature for 15-105 min (t s ) and then cooled inside the furnace to room temperature.…”

“…6 shows the growth conditions that result in the pure Bi2212 phase and perfect c-axis orientation of Bi2212 films grown on MgO and LAO substrates. The phase formation temperature region (1094-1100 K) of Bi2212 grown on STO substrates following the literature (Lu et al, 2013) is also plotted in Fig. 6.…”

“…molecular beam epitaxy and pulsed laser deposition methods). In our previous work, Bi2212 superconducting thin films were prepared by the Pechini sol-gel method (Pechini, 1967) using nitrates as reactants (Lu et al, 2013). The results showed that the purity and physical properties of Bi2212 films grown on SrTiO 3 (100) substrates were remarkably enhanced as a result of the preparation of a uniform and stable precursor gel , providing a potential process to improve the purity and crystallinity of Bi2212 thin films.…”