HOLE DOPING IN TL2BA2CUO6+DELTA (TC=0-80 K) INVESTIGATED BY TI-205 NUCLEAR-MAGNETIC-RESONANCE

Single phase samples of Tl2Ba2CuO6+δ with a Tc between 80 K and less than 4 K were investigated by 205Tl NMR experiments indicate that the oxidation state of the thallium ions is predominantly 3+. The resonance line shapes, line positions and spin-lattice relaxation times as well as their temperature dependences are comparable for all samples of Tl2Ba2CuO6+δ, irrespective of their Tc. Redistribution of holes between TlO layers and CuO2 planes can hence be disregarded. The hole concentration in Tl2Ba2CuO6+δ is dominated by the amount of excess oxygen in the TlO layers. The change in Tc with the relative change in oxygen content suggests that the phase diagram of Tl2Ba2CuO6+δ is comparable to that of La2-xSrxCuO4, YBa2Cu3 O6+x, Bi2Sr2CuO6+δ and Bi2Sr2CaCu2O8+δ. This leads to the conclusion that nominal Tl2Ba2CuO6+δ samples may be regarded as being overdoped with holes. © 1990.