Oxygen ordering effects and the superconducting transition temperature Tc of YBa2Cu3Ox under pressure

https://doi.org/10.1016/0921-4534(94)92114-8Get rights and content

Abstract

The superconducting transition temperature Tc of YBa2Cu3Ox depends strongly on the oxygen content x and the degree of oxygen ordering in the CuO-chains. This oxygen ordering can be influenced drastically by storing an oxygen deficient sample at temperatures Ts above 240K. At lower temperatures the degree of oxygen ordering is preserved, even when pressure is applied. Therefore applying pressure at low temperatures close to Tc results in a Tc increase that is not affected by oxygen ordering. This intrinsic pressure effect (dTc/dp)i deponds strongly on the oxygen content x and shows a distinct maximum of 7.4K/GPa at x=6.72. For samples close to the maximum oxygen content x=7.0 the intrinsic pressure effect is almost zero. For some single crystals negative (dTc/dp)i values have been observed at this oxygen content.

If a sample is stored at temperatures Ts above 240K pressure induced oxygen rearrangement is possible. This causes a Tc relaxation under pressure. The Tc increase due to a completed oxygen reordering under pressure (dTc/dp)o has a maximum at x=6.72, too. At x close to 7.0 this additive pressure effect vanishes according to the lack of oxygen ordering possibilities.

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