Dependence of oxygen stoichiometry and critical temperature of Bi2Sr2CaCu2O8+Δ on oxygen partial pressure between 300 and 700 deg. C

The oxygen non-stoichiometry of Bi2Sr2CaCu2O8+δ was explored by thermogravimetry between 300 and 700 deg. C under various oxygen pressures (PO2) ranging between 10-4 and 1 atm under conditions of thermodynamic equilibrium. The departure from stoichiometry Δ splits into two domains δr + δ*. The former δr is a residual oxygen content. The latter δ* depends on temperature and oxygen pressure. δ* is related to the formation of oxygen interstitials, the concentration of which depending on P+1/6O2. Several samples corresponding to various departures from stoichiometry have been prepared to measure the critical temperature, by SQUID magnetometry, displaying the underdoped and overdoped ranges. (author)