EFFECT OF SAMPLE DENSITY ON MAGNETIC PENETRATION DEPTH IN YBACUO CERAMIC SUPERCONDUCTORS

We have measured magnetic penetration depth lambda(0) of high-T-c YBCO samples of different density by the cavity resonant frequency shift m ethod at 10, 16.65, and 22.3 GHz microwave frequencies. The value of l ambda(0) at 10 GHz is found to decrease from 5850 Angstrom to 2550 Ang strom as the density of the sample increases from 4.4 to 5.3 g/cm(3). The results of the frequency response of the penetration depth show a fairly constant value of lambda(0) for all the three samples in the fr equency range 10-22.3 GHz. The wide variation observed in the value of lambda(0) for different density samples has been explained in terms o f varying Josephson coupling strength in these ceramics.