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

초록

To unveil the structural changes associated with T<inf>c</inf> variations induced by oxygen incorporation in Ph-based 1212 system, we have performed neutron diffraction experiments on two samples of (Pb,Ti)(Sr,Ba)<inf>2</inf>(Ca,Y)Cu<inf>2</inf>O<inf>7+δ</inf> with different oxygen contents(δ = 0.06 and 3.17). The T<inf>c</inf> of the oxygenated sample(δ = 0.17) was below 15 K and that of the deoxygenated sample(δ = 0.06) was 21 K. Thermopower measurements reveal that both oxygenated 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 reduced in the deoxygenated sample. The length of the Cu-O bond on the CuO<inf>2</inf> conduction plane decreases from .921 Å to 1.918 Å, 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 the hardening of about 540 cm-1 Raman peak. The bond valence sum for the Cu on the CuO<inf>2</inf> plane increases slightly by the deoxygenation. This observation provides evidence for the idea that the removal of the excess oxygen in the Pb-basal plane increases the hole density on the CuO<inf>2</inf> plane to raise T<inf>c</inf>.