17O NMR in high- Tc superconductor Tl 2Ba 2CaCu 2O y

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17O NMR measurements have been performed between 10 and 400 K on an overdoped sample of Tl 2Ba 2CaCu 2O y ( T c = 103 K). The electric field gradient parameters were deduced for all the oxygen sites. The temperature dependence of the magnetic hyperfine shift was measured for all these sites. No thermal variation of the shift was detected down to T c for oxygen in the TlO reservoir plane. As for oxygen in the CuO 2 plane the temperature dependence of the shift is similar to that for 205Tl NMR line from thallium defects in the Ca layer measured in the same powder sample. This similarity is consistent with the single spin fluid model. The spin contribution to 17K iso( T) and magnetic hyperfine constant 17A iso were deduced.