Long time relaxation of resistance in La0.8Sr0.2MnO3 ceramics and La0.65Ca0.35MnO3 films on ferroelectric substrates

Galvanomagnetic properties of La0.65Ca0.35MnO3 films with a thickness of 0.2 mum on Pb2.9Ba0.05Sr0.05(Zr0.4Ti0.6)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 La0.8Sr0.2MnO3 and La0.6Sr0.2Mn1.2O3 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+DeltaRexp(-t/tau). The magnitude of LTR is 5-10 time greater then fast variation of resistance under action of stress. The sign of DeltaR is dependent on the kind of stress. The time constant (tau) has the value of 3-9 hours. (C) 2004 WILEYNCH Verlag GmbH & Co. KGaA, Weinheim.