Thin Films of High Tc Superconductors, Ag-doped YBCO

1.1 A study of thin films of Ag-doped YBCO
A study of thin films of Ag-doped YBCOwas initiated as silver was found to be an inert (noble) material in YBCO. It was also realized early that all characteristics of Ag-doped films were superior to that of undoped YBCO. The targets were higher densities, deposition was lower, Tc was high and consistent and Jc was higher. Elaborate controlled experiments were then initiated to understand the reason for this improvement. Our findings are highlighted below,

Silver provided nascent oxygen to the growing film and improved oxygenation
Silver acted like a surfactant, thus improving the lateral mobility of the add-atoms (YBCO) and improving the aligning of the grain to the substrate lattice.
Silver is inert and very mobile at growth temperatures and gets squeezed by the growing grains thus allowing the enlargement of the growing grain.

BEST RESULTS are

Highest reported critical current density,

Jc = 0.8 to 1.4 x 10⁷ A/sq cm at 77K for Ag-doped YBCO on SrTiO₃ substrate

Dhananjay Kumar, M. Sharon, R.Pinto, P.R. Apte, S.P. Pai, S.C. Purandare, L.C. Gupta and R. Vijayaraghavan, "Large critical currents and improved epitaxy of laser ablated Ag-doped YBa₂Cu₃O_7-dthin films", Appl. Phys. Lett. 62 (1993) 3522.
[cited 49 times]
[Highest critical current of 1.4 x 10⁷ Amp/sq. cm. for YBCO films]

Lowest reported microwave surface resistance

Rs = 210 micro-ohm at 77K and 10GHz

R. Pinto, Navdeep Goyal, S.P. Pai, P.R. Apte, L.C. Gupta, R. Vijayaraghavan, "Improved microwave performance of Ag-doped YBa₂Cu₃O_7-dthin film microstrip resonators", J. Appl. Phys. 73 (1993) 5105.

[cited 36 times]

[Lowest surface resistance of 210 microohm-cm for YBCO films]

Our papers on Ag-doping are cited often (49 citations for Jc and 36 citations for Rs) and Ag-doping is being used by many laboratories around the world.

Use of Au-doping was first proposed by me as the best possible grain boundary passivation to improve not only the microstructure but also improve the stability of the film. Our work on accelerated aging has indeed shown an improvement by 2 orders of magnitude in stability.

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