Interfacial coupling and its size dependence in PbTiO₃ and PbMg_1/3Nb_2/3O₃ multilayers

Abstract

Multilayers of Pb(Mg_1/3Nb_2/3)O₃ (PMN)-PbTiO₃ (PT) were deposited through pulsed laser ablation deposition with different periodicities (d=10,20,30,40,50,60, and 70 nm) for a constant total thickness of the film. The presence of superlattice reflections in the x-ray diffraction pattern clearly showed the superlattice behavior of the fabricated structures over a periodicity range of 20-50 nm. Polarization hysteresis and the capacitance-voltage characteristics of these films show clear size dependent ferroelectric and antiferroelectric (AFE) characteristics. Presence of long-range coupling and strain in multilayers with lower periodicity (~10 nm) exhibited a clear ferroelectric behavior similar to a solid solution of PMN and PT. Multilayers with higher periodicities (20-50 nm) exhibited antiferroelectric behavior, which could be understood from the energy arguments. On further increase of periodicity, they again exhibit ferroelectric behavior. The polarization studies were carried out beyond the Curie temperature T_c of PMN to understand the interlayer interaction. The interaction is changed to a ferroelectric-paraelectric interlayer and tends to lose its antiferroelectric behavior. The behavior of remnant polarization P_r and dP_r/dT with temperature clearly proves that the AFE coupling of these superlattices is due to the extrinsic interfacial coupling and not an intrinsic interaction as in a homogeneous conventional AFE material. The evidence of an averaged behavior at a periodicity of ~10 nm, and the behavior of individual materials at larger periodicities were further confirmed through dielectric phase transition studies. The presence of AFE interfacial coupling was insignificant over the dielectric phase transition of the multilayers.