In situ measurements during MeV ion bombardment at room temperature are used to study the superlinear increase of resistivity with fluence which occurs in irradiated ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$. The functional form of the resistivity increase is found to be exactly exponential for O and As ion irradiation, confirming previous results of lower precision. For low ion damage rates we find deviations from the exponential dependence at low doses. We show that these are caused by an unidentified phase transformation, occurring during the irradiation, which lowers the resistivity of the samples. Annealing of resistivity increments caused by brief irradiations occurs at room temperature, indicating that radiation-induced defects are mobile. The rate of annealing is strongly sample dependent, but in all cases the transformation induced by a small dose of irradiation causes a reduction in the resistivity of the sample. We suggest that the reduction in resistivity may be due to ordering on the oxygen sublattice.

• Received 25 January 1989

DOI:https://doi.org/10.1103/PhysRevB.39.9061