Oxygen-Ordering Effects in High-T_c Superconductors
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In the superconducting oxides the value of T<SUB>c</SUB> may be a sensitive function of both the concentration and the distribution of oxygen defects, the latter quantity itself being a function of both temperature and pressure. Recent high-pressure experiments on Tl<SUB>2</SUB>Ba<SUB>2</SUB>CuO<SUB>6+y</SUB> have revealed distinct low- and high-temperature relaxation processes above 15 K, presumably originating in the oxygen sublattice. In TlSr<SUB>2</SUB>CaCu<SUB>2</SUB>O<SUB>7-y</SUB> and YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>6, 41</SUB> only relaxation above 250 K is observed. The relaxation time τ in YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>6, 41</SUB> is found to increase rapidly with pressure from approximately 10 hours at 1 bar to 550 hours at 2. 3 GPa. In systems where such relaxation effects occur, T<SUB>c</SUB> is thus not a unique function of pressure, but rather depends in a complicated way on the pressure-thermal-time prehistory of the sample.
- The Review of High Pressure Science and Technology
The Review of High Pressure Science and Technology 7, 425-430, 1998
The Japan Society of High Pressure Science and Technology