Millimeter wave surface resistance of grain-aligned Y1Ba2Cu3Ox bulk material

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Abstract
We report measurements of the millimeter wave surface resistance of grain‐aligned YBa2Cu3Ox bulk material grown by a liquid phase process. The measurements were performed by replacing the endplate of a TE011 cylindrical copper cavity with the superconducting sample. Surface resistance was measured for samples with surfaces oriented perpendicular and parallel to the c‐axis of the grains. We show that, for the parallel configuration, the surface resistance at 77 K and 80 GHz is typically near 100 mΩ. For a very well‐aligned sample with a very low density of Y2BaCuOy precipitates, measured in the perpendicular configuration, the transition width (10%–90%) is about 2 K and the surface resistance is less than 50 mΩ at 88 K. The effect of microstructure on surface resistance is discussed.