The special AgNO3 induced formation of YBa2Cu4O8 thin films through spray pyrolysis

A new synthesis route for the formation of HTSC films of YBa2Cu4O8 on a viable substrate e.g. MgO by spray pyrolysis has been found through the addition of AgNO3 in appropriate solution mixture. The AgNO3 works as a rate enhancer catalyst which on dissociation during the film processing at ∼ 805 deg. C supplies active oxygen necessary for the synthesis of HTSC YBa2Cu4O8. The transition Tc(R=0) for the present YBa2Cu4O8 film was found to be ∼ 78 K for an Ag concentration of 0.10. The observed Tc is comparable with Tc values of YBa2Cu4O8 film prepared through other routes. In addition AgNO3 through dissociation also provides Ag, which enters the grain boundaries, leading to their passivation. The silver also appears to act as a surfactant, resulting in an enlargement of grain size (e.g. 1.0 to 5.0 μm for Ag concentrations of 0.05 and 0.10 respectively). Both these effects ensuing from Ag lead to an enhancement of critical current density, Jc. The optimum Jc of ∼ 7.8x104 A cm-2 at 16 K has been found for the Ag concentration of 0.10. Thus in the present synthesis of YBa2Cu4O8 films, both the supply of oxygen required for development of YBa2Cu4O8 HTSC phase and enhancement of critical current density based on grain boundary passivation and enlargement of grain sizes (decrease of grain boundary density) have been obtained by the singular process of addition of an appropriate concentration of AgNO3. (author)