Variations in the Far-Infrared Reflectivity of Ba sub 2 YCu sub 3 O sub x.

We present an empirical summary of the far-infrared reflectivity of 18 samples Ba sub 2 YCu sub 3 O sub x, with emphasis on 10 oriented, microtwinned crystals with x nominally near 7. The results vary among samples indicating that further work will be necessary to identify the intrinsic behavior to our satisfaction. At this stage, the general behavior allows us to rule out a constant relaxation rate for charge carriers and to make only general remarks concerning the superconducting energy gap.