Annealing temperature and O2 partial pressure dependence of T c in HgBa2CuO4+δ

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Abstract
Samples of HgBa2CuO4+δ (Hg‐1201) were annealed under various conditions. After carefully controlling annealing time, annealing temperature (Ta), and O2 partial pressure (P0), we were able to find the reversible annealing conditions for Hg‐1201. Under 1 atm O2 at 260 °C≤Ta≤400 °C, the obtained Tc is nearly the same (∼97 K). However, it decreases quickly with Ta≳300 °C in high vacuum (P0∼10−8 atm), and reaches zero at Ta=400 °C. On the other hand, Tc decreases with the decrease of Ta in high‐pressure O2 (∼500 atm) and reaches ∼20 K at about 240 °C. In the entire annealing region, the oxygen surplus varies significantly from 0.03 to 0.4, and a wide range of Tc variation (0→97 K→20 K) was obtained with anion doping alone.

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