ELECTRIC-FIELD GRADIENT MEASUREMENTS ON CD-111 IN THE HIGH-T-C SUPERCONDUCTOR BI1.7PB0.3SR2CA2CU3OY

The electric field gradients (EFGs) in the sites of a Cd-111 probe nuc leus have been measured by the perturbed angular correlation (PAC) met hod in the high-T-c superconductor Bi1.7Pb0.3Sr2Ca3Cu3Oy between 77 an d 473 K. The probe atoms sense two defined EFGs with quadrupole coupli ng constants of 90(3) and 67(1) MHz, and asymmetry parameters of 0.51( 3) and 0.30(2) at 300 K which were assigned to Bi-and Ca-sites, respec tively. The frequency distribution broadening of the Bi-site has been observed, and this broadening is due to charge inhomogeneity surroundi ng the Pi-site which is interpreted by Pb-doping and structure modulat ion of the Bi layer. The frequency distribution broadening in the Ca-s ite has been also observed.