Dielectric and electromechanical properties of Pb(Mg1/3,Nb2/3)O3–PbTiO3 thin films grown by pulsed laser deposition

Pulsed laser deposition was used to grow thin films of several compositions from the ${\mathrm{Pb(Mg}}_{\text{1/3}},{\mathrm{Nb}}_{\text{2/3}}){\mathrm{O}}_3–{\mathrm{PbTiO}}_3\mathrm{ (}\mathrm{PMN–PT})$ solid solution as dielectric layers in thin film capacitor structures. They were found to display functional behavior characteristic of relaxors, with the only significant difference between thin film and bulk being a severely reduced dielectric permittivity. Room temperature polarization loops showed a general increase in both the remanent polarization and absolute magnitude of the polarization for a given field with PT content. The electric field-induced strain was primarily examined by in situ x-ray diffraction and although fields greater than 20 MV m⁻¹ were applied to the films, the maximum observed strain was only ∼0.3%, considerably less than the 1.4% seen in single crystal samples. Piezo-response atomic force microscopy studies were consistent in that the macroscopic effective piezoelectric coefficient $d_{33},$ was found to differ from single crystal measurements by an order of magnitude. However, electrostrictive coefficients ${\mathrm{(Q}}_{33}\mathrm{),}$ were found to be comparable to published values for both PMN–PT single crystals and ceramics, ranging between 1 and ${\text{9×10}}^{\text{−2}} {\mathrm{C}}^{\text{−4}} {\mathrm{cm}}^2.$ Consequently, it seems that the relatively poor strain response in these thin films is intimately linked to the reduced permittivity and not to a fundamental difference in the electrostrictive coefficients between bulk and thin film.