Superconducting Hg-Ba-Ca-Cu-O thin films on lanthanum aluminate and sapphire substrates

Epitaxial c-axis-oriented HgBa/sub 2/CaCu/sub 2/O/sub 6+(delta)/ (Hg-1212) thin films have been prepared on lanthanum aluminate as well as on CeO/sub 2/ buffered r-plane sapphire substrates using a Tl-Hg cation-exchange process. Films on LaAlO/sub 3/ exhibited superconducting transition temperatures (T/sub c/) up to 122 K and critical current densities in the range of 2.2-3.1 MA/cm/sup 2/ at 77 K and under self-field. For the microwave surface resistance (R/sub s/) values of ~4 m(Omega) at 17.86 GHz and 77 K have been obtained. In comparison, films on sapphire substrates with T/sub c/ values up to 118 K showed critical current densities in the range of 0.7-1.0 MA/cm/sup 2/ and R/sub s/ values of ~7 m (Omega). With further optimization of processing an improvement of superconducting properties of Hg-1212 films on sapphire substrates is expected.