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Session Q09 - HTSC: STRUCTURES AND DEFECTS
Mixed session, Friday morning, March 24, 8:00
Ballroom A5, San Jose Convention Center
The dependence of the superconducting transition temperature on pressure T _c (P) has been determined for Tl _2 Ba _2 CuO _6+\delta and TlSr _2 CaCu _2 O _7-\delta at different oxygen concentrations. The pressure derivative dT _c /dP is found to depend strongly on the temperature at which the hydrostatic He-gas pressure is applied. This result is believed to originate from pressure-induced ordering of oxygen defects at ambient temperature, a process which is prevented by sluggish kinetics if the pressure is changed at low temperatures (50 K). A detailed study of both T _c and the Hall number n _H as function of pressure, temperature and time reveals distinct ''fast'' and ''slow'' relaxation processes in the oxygen defect subsystem. Related oxygen ordering effects may be quite common in the high-T _c oxides. Evidence is discussed for the existence of ''fast'' oxygen ordering processes in YBa _2 Cu _3 O _7-y which may be responsible for ''transient photo-induced superconductivity''.
*Research supported by NSF grant DMR-9208531.