Hysteretic effect of sound velocity in sintered Bi2Sr2CaCu2O8 + δ with excess oxygen

Abstract To explore the relationships between a thermal hysteretic effect of sound velocity and excess oxygens, the temperature dependence of the sound velocity in sintered Bi 2 Sr 2 CaCu 2 O 8 +δ has been measured. To vary the oxygen content, samples have been annealed in different atmospheres (nitrogen, air, oxygen) and then furnace-cooled to room temperature or quenched in liquid nitrogen. The thermal hysteresis has been observed only in the quenched samples but not in furnace-cooled samples. It is shown that this hysteresis is related to both the excess oxygen content and the quenching process.