We have determined the local structure of Tl-2(Ba1-xSrx)(2)CuO6, with
x=0.0, 0.4, 0.5 and T-c=89 K, 57 K, 0 K, respectively, using X-ray abs
orption fine structure at both the Cu K and Tl L(III) edges. As the st
rontium concentration increases from x=0.0 to 0.5, the copper-in-plane
oxygen distance decreases from 1.94 Angstrom to 1.90 Angstrom, the co
pper-copper distance from 3.88 Angstrom to 3.81 Angstrom, and the copp
er-axial oxygen (0(2)) distance from 2.71 Angstrom to 2.65 Angstrom, w
hile the thallium-axial oxygen (0(2)) distance remains at 2.00 Angstro
m, indicating an overall unit-cell contraction. We also find that the
strontium atom is 0.14 Angstrom closer to the CuO2 plane than the bari
um atom. The contraction of the copper-in-plane oxygen bonds reflects
an increase in the hole concentration in the CuO2 plane, leading to th
e observed decrease of T-c due to hole overdoping.