NONLINEAR MICROWAVE-ABSORPTION IN BA1-XKXBIO3

Nonlinear, field-modulated, direct microwave absorption (FMMA) was obs erved in copper-free Ba1-xKxBiO3 powder samples. The high-field, low-t emperature results were compared to previous measurements of YBa CuO a nd BiSrCaCuO. The microwave determined critical field mu0H = 0.7 muT and depinning current density J(c) almost-equal-to 1 X 10(7) A/m2 wer e obtained from the ''Portis'' model of flux pinning and depinning. Th ese values were lower than the values obtained previously for YBaCuO a nd BiSrCaCuO as anticipated for a material with larger coherence lengt h and comparable London penetration depth. A previously unobserved asy mmetry of the FMMA in the field scan direction was also noted.