Detection of ionic mobility in YBa₂Cu₃O₇-δ by means of the phase-sensitive rejection-filtering technique

Abstract To investigate potential ionic migration in YBa2Cu3O7 -δ films (a-b plane) as a function of temperature T, a 1 Hz square-wave current is sent through the a-b plane. The resulting voltage V in phase with the current is rejected by means of a new phase-sensitive filtering technique to isolate a weak, slowly responding component V 1 which is caused by minute ionic diffusion. This residual component is further processed into a final signal S. This S shows a striking sharp increase at the ‘transition temperatures’ T q close to 208, 257, 310, 345 and 380K as T is increased from 77 K. The slope of S increases progressively with increasing T. The T q values depend on the thermal history of the samples. The observed discontinuities of S at the T q seem to correspond to the broad elastic anomalies reported previously near these temperatures.