Results of recent investigations are analyzed pertaining to the real and im
aginary parts of the surface impedance Z(s) = R-s + iX(s) of high-quality,
high-T-c single crystals of YBa2Cu3O6.95, Ba0.6K0.4BiO3, Tl2Ba2CaCu2O8-delt
a, Tl2Ba2CuO6+delta, and Bi2Sr2CaCu2O8. Characteristic features of the temp
erature dependence of the surface impedance are pointed out. Published mode
ls are mentioned which investigate the typical features of these materials.
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