Influence of oxygen content on the activation energy for oxygen ordering in Tl2Ba2CuO6+δ

The activation energies EA for both low temperature (LT) (<120 K) and high temperature (HT) (>200 K) oxygen ordering processes in Tl2Ba2CuO6+δ single crystals have been estimated from the time dependence of Tc following the release of high pressure (0.6 GPa) at low temperatures. The crystals studied have Tc values of 29 K (strongly overdoped), 40 K (moderately overdoped), and 70 K (slightly overdoped). For both HT and LT processes EA is clearly largest for the 29 K sample; for the HT process EA appears to be slightly smaller for the 40 K sample than for the 70 K sample, but approximately equal for the LT process. Possible mechanisms are discussed.