Evidence in the elastic properties for a stress-related phase transition in the high-${\mathit{T}}_{\mathit{c}}$ material: ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{\mathit{x}}$

We have measured the stress-strain properties of whiskerlike samples of the high-${\mathit{T}}_{\mathit{c}}$ material ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{\mathit{x}}$. We observe an anomalous temperature dependence of Young’s modulus (Y) around 300 K. The magnitude of Y falls by a factor of 3–4 between 270 and 330 K. We also observe hysteresis in the stress-strains curves in this same temperature range. The stress and strain relax toward the middle of the hysteresis loop with a characteristic time of approximately 20 sec. All these phenomena are reproducible as either the stress or temperature is cycled.