Critical temperature studies of multiphase oxocuprates

Abstract

An exploratory study of critical temperatures (T_c) in multiphase oxocuprates examines the relation between T_c values and crystal field effects induced by chemical compositional variation. Onset T_c of some yttrium barium and bismuth barium oxocuprates are measured by the electron paramagnetic resonance (EPR) technique at zero/remnant magnetic fields. A sealed-tube preparation of 123-YBCO (yttrium barium oxocuprate) in 2-8 bar oxygen suppresses the onset T_c to below 77 K. An unidentified phase formed at 1 000 K in 2223-BB000 (bismuth barium calcium oxocuprate) with an onset T_c of 85 K. A resonant virtual phonon exchange mechanism is proposed to account for the vulnerability of superconducting phase material to compositional change.