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

The oxygen non-stoichiometry of Bi2Sr2CaCu2O8+Delta was explored by thermogravimetry between 300 and 700 degrees C under various oxygen pressures (Po-2) ranging between 10(-4) and 1 atm under conditions of thermodynamic equilibrium. The departure from stoichiometry a splits into two domains delta(r) + delta*. The former delta(r) is a residual oxygen content. The latter delta* depends on temperature and oxygen pressure. delta* is related to the formation of oxygen interstitials, the concentration of which depending on p(O2)(+1/6). 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.