MOISTURE-ENHANCED STRENGTH DEGRADATION OF A SUPERCONDUCTING CERAMIC

In this letter the 'dynamic-fatigue' effect is demonstrated and a parameter for use in predicting ceramic failure-lifetime, is measured for the orthorhombic superconducting compound YBa//2Cu//3O//7// minus //x. Values of fracture toughness are also assessed for the hot-pressed and pressureless-sintered ceramics. The data demonstrate a significant dynamic-fatigue phenomenon in homogeneous, high-density, superconducting ceramics based on the YBa//2Cu//3O//7//M//I//N////x phase. It enables a prediction of lifetim under stress in atmospheres containing water vapor but the effect is of a severity which will dictate the hermetic encapsulation of superconductors unless they are permanently retained in dry cryogenic fluids. The relatively low values for fracture toughness are typical of monolithic oxide ceramics. 7 Refs.