In-plane versus out-of-plane dielectric response in the thin-film relaxor Pb(Sc1/2Ta1/2)O3

The nature of the strongly reduced dielectric permittivity in relaxor ferroelectric thin films is addressed. This reduced response has often been attributed to passive or surface layers in series with the film capacitance. The present report presents evidence in contradiction to this scenario in relaxor thin films by comparing the properties determined in two different measurement configurations termed "out-of-plane" versus the "in-plane" dielectric response. The analysis of the dielectric properties of Pb(Sc1/2Ta1/2)O-3 films processed in a similar fashion on Pt/Ir/MgO substrates measured out-of-plane, and directly on MgO substrates measured in-plane showed that a passive layer is not the predominant effect for the reduction of permittivity by an order of magnitude for thin films as compared to bulk ceramics. This conclusion is confirmed by the results of the out-of-plane dielectric response as a function of the film thickness. It is concluded that the origin of the reduced dielectric response in relaxor thin films should be sought in the structural and microstructural properties of the film itself rather than in its interfacial properties.