Long time relaxation of resistance in La _0.8 Sr _0.2 MnO ₃ ceramics and La _0.65 Ca _0.35 MnO ₃ films on ferroelectric substrates

Abstract

(Zr 0.4 Ti 0.6 )O 3 ferroelectric ceramics substrates have been investigated. We have dicovered the monotonic irreversible increase of the film resistance by 3-5 time of value during several hours after multiple inversion of substrate polarization. The long-time relaxation (LTR) of film resistance is explained by dielecrtrization of film intercrystallite boundaries as a result of oxygen redistribution under action of inhomogeneous mechanical stress. In addition, the LTR of resistance of La 0.8 Sr 0.2 MnO 3 and La 0.6 Sr 0.2 Mn 1.2 O 3 ceramic samples has been investigated under action of different kind of mechanical stress: stretch, compression and hydrostatic press. Time dependence of resistance is described by R 0 +∆Rexp(-t/τ). The magnitude of LTR is 5-10 time greater then fast variation of resistance under action of stress. The sign of ∆R is dependent on the kind of stress. The time constant (τ) has the value of 3-9 hours.