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

The effect of chemical doping and hydrostatic pressure on Tc of Y1−yCayBa2Cu3Ox single crystals

“…An influence of pressure on oxygen ordering was found for the Tl221 compound at temperatures even below 40 K [75][76][77][78][79]. Similar processes were seen for Y123 [69,[80][81][82][83][84][85] but in contrast to Tl221 it was shown by T c (p) determinations that the oxygen ordering effect was absent at temperatures below 240 K [80]. As those authors had to go above T c to determine the appropriate T c values of their samples they mentioned possible low temperature relaxation processes that might have caused unknown structural changes.…”

“…As those authors had to go above T c to determine the appropriate T c values of their samples they mentioned possible low temperature relaxation processes that might have caused unknown structural changes. Klehe et al [78] argued that low temperature oxygen ordering may exist and that it could be responsible for the peak in dT c /dp at an oxygen content of x=6.7 [82]. However, pressure induced oxygen ordering was absent for an Y123 sample with an extremely low oxygen content x=6.41, as shown by Sadewasser et al [79].…”

“…T c was determined by ac susceptibility measurements using the peak in χ" as T c criterion. In order to avoid pressure induced oxygen ordering effects [79][80][81][82][83] pressure was applied at low temperature (T ≤ 110 K) and the sample was kept at temperatures below 110 K during the whole experiment. At the beginning and the end of the experiment T c was measured at ambient pressure.…”

“…However, pressure induced oxygen ordering was absent for an Y123 sample with an extremely low oxygen content x=6.41, as shown by Sadewasser et al [79]. Due to the low T c of that sample it was proofed that no oxygen ordering effects occur between temperatures of 14 K and 250 K. Although relaxation processes at temperatures below 14 K can not be ruled out, it is clear that experiments on oxygen deficient Y123 with pressure application above or below 240 K will result in different dT c /dp values due to the resulting enhanced T c values from oxygen ordering [81,82]. This is one reason for the large scatter in the comparison of early experiments.…”

Effect of high pressure on the fluctuation conductivity and the charge transfer of YBa2Cu3O7− single crystals

“…The absence of a microscopical theory of high-temperature superconductivity (HTSC) constitutes the significance of experimental methods that enable the study of parameters affecting the physical characteristics in the normal and in the superconducting conditions. In this respect, the application of experimental techniques employing high pressures [4][5][6][7][8][9] is significant.…”