Thin-film growth and compositional effects in YBa2Cu3O7−<i>x</i> layers prepared by metalorganic chemical vapor deposition

Abstract

Thin-film growth and compositional effects of c-axis oriented YBa2Cu3O7−x (YBCO) thin films synthesized by metalorganic chemical vapor deposition have been investigated. The formation of single cation films using tetramethylheptanedionate precursors was shown to be mass controlled, exhibiting a ratio of deposited to evaporated species in the increasing order Ba, Y, and Cu. The physical properties of off-stoichiometric YBCO films deposited on MgO substrates were measured in the compositional range 1.1≤Ba/Y≤2.3 and 1.5≤Cu/Ba≤4.6. While structural properties such as c-axis values and rocking curves appeared unaffected to variations in cation stoichiometry, morphology was observed to be extremely sensitive even to slight changes in composition. Off-stoichiometric layers with Cu/Ba≳1.5 were observed to exhibit Cu-rich precipitates embedded in a 1:2:3 YBCO film matrix. The zero-resistivity temperatures were above 77 K for all cation film compositions measured. However, sharp ac-susceptibility transitions were restricted to a more narrow compositional range (1.9&amp;lt;Cu/Ba&amp;lt;3.6). The best superconducting properties [Tc=85 K, Jc (77 K)≳106 A/cm2] were observed for films with relatively rough surface morphologies (Ba/Y=1.6 and Cu/Ba=3.5). An optimum trade-off between smooth surfaces and superconducting properties was found for Ba/Y=1.5 and Cu/Ba=1.9, yielding Tc=81 K and Jc (77 K)=3×105 A/cm2.