Composition control and electrical properties of PMN-PT thin films around the morphotropic boundary

We have successfully grown (1-x)Pb(Mg_1/3- Nb_1/3)O₃-xPbTiO₃ (PMN-PT) thin films with x=0.3, 0.35 and 0.4 by pulsed laser deposition. X-ray-diffraction studies reveal that the PMN-PT films grown on La_0.5Sr_0.5CoO₃/LaAlO₃ substrates form epitaxial heterostructures. Composition control and remedial measures to compensate for the lead and magnesium losses due to re-evaporation are demonstrated. As a common feature, the as-grown PMN-PT thin films exhibit a self-poling behavior. Their dielectric constants measured at room temperature vary from 1500 to 2500, depending on the PMN to PT ratios. The pyroelectric coefficient of the films varies from 160 to 300 C/m²K. The piezoelectric coefficient d₃₃ is around 27 pm/V in the as-grown 70/30 films. A comparison of these values with the bulk PMN-PT of same compositions implies that the much-reduced piezoelectric properties in the PMN-PT films are primarily due to a substrate-clamping effect. PACS 77.84.-s; 77.65.-j; 77.80.-e