Millimeter wave absorption of Y-Ba-Cu based high T/sub c/ superconductors

Microwave absorption of yttrium-barium-copper oxides has been measured by using an open resonator technique in the temperature range of 20 K to the samples´ critical temperatures and beyond. The samples with the start stoichiometries characterized as Y/sub 4/Ba/sub 7/Cu/sub 11/O/sub x/, Y/sub 5/Ba/sub 6/Cu/sub 11/O/sub x/, YBa/sub 2/Cu/sub 3/O/sub x/, and Y/sub 2/Ba/sub 4/Cu/sub 8/O/sub x/ have indicated a sharp drop in their temperature-dependent surface resistance or the normal to superconducting phase transition in the range of 84 to 92 K. The results indicated that the 123 superconducting phase was most favorable to high T/sub c/ and low absorption. Significant absorption in the materials was observed at a temperature well below the T/sub c/, which may be associated with the intrinsic behavior of the materials. It is suggested that the anisotropy both in structure and electromagnetic behavior of these materials might be one of the dominant factors.<>