High Temperature Superconductivity at 30K in (Ba, K)BiO sub 3 .

Several basic physical properties of the 30K superconductor Ba sub (0.6) K sub (0.4) BiO sub 3 have been measured. From the upper and lower critical field slopes near T sub c , the density of states of E sub f was estimated and found to be 2.2 +- 0.4 times higher than in BaPb sub (0.75) Bi sub (0.25) O sub 3 , similar to results of band structure calculations. The normal state susceptibility is essentially temperature independent and consists of a dominant diamagnetic core contribution and a smaller paramagnetic contribution, which is proportional to the superconducting volume.