Effect of Oxygen incorporation on the Local structure of (Pb,Ti)(Sr,Ba)(2)(Ca,Y)Cu2Oz

To unveil the structural changes associated with Te variations induced by o xygen incorporation in Pb-based 1212 system, we have performed neutron diff raction experiments on two samples of (Pb,Ti)(Sr,Ba)(2)(Ca,Y)Cu2O7+delta wi th different oxygen contents(delta = 0.06 and 0.17). The T-c of the oxygena ted sample(delta = 0.17) was below 15 K and that of the deoxygenated sample (delta = 0.06) was 21 K. Thermopower measurements reveal that both oxygenat ed and deoxygenated samples are in the underdoped state and the removal of the excess oxygen by the deoxygenation-treatment results in an increase in the carrier density. The neutron diffraction data indicates that the excess oxygen in the oxygenated sample partially occupies a 2f(0, 1/2, 0) site on a (Pb,Ti)-O basal layer, whereas occupation of this site found to be reduc ed in the deoxygenated sample. The length of the Cu-O bond on the CuO2 cond uction plane decreases from 1.921 Angstrom to 1.918 Angstrom, while the Cu- O(2) bond length increases upon oxygen removal and thereby the (Pb,Ti)-O(2) bond length decreases which is consistent with tile hardening of about 540 cm(-1) Raman peak. The bond valence sum for the Cu on the CuO2 plane incre ases slightly by the deoxygenation. This observation provides evidence for the idea that the removal of the excess oxygen in tile Pb-basal plane incre ases the hole density on the CuO2 plane to raise T-c.