Influence of oxygen content on dielectric and electromechanical properties of Pb(Mg1/3Nb2/3)O3 thin films

Pulsed laser deposition was used to grow Pb(Mg1/3Nb2/3)O3 (PMN) thin film planar capacitor structures. X-ray diffraction and plan-view transmission electron microscopy were used to verify PMN crystallography. The dc leakage current and ac capacitance and dielectric loss were measured as a function of temperature and frequency. Finally, crystallographic strain as a function of applied dc field was monitored in situ by x-ray diffraction. The electromechanical strain response was found to depend on the deposition conditions for each capacitor. Tensile strains of ∼0.2% and compressive strains of ∼0.35%, both parallel to the applied field, were measured for capacitors of different oxygen contents and thicknesses. Tensile strains achieved are higher than previously reported for PMN thin films or polycrystalline ceramics. We propose that the compressive strains are not an intrinsic property of the PMN. Instead they are induced by the combined effect of joule heating of the capacitor structure, caused by leakage currents, and thermal expansion mismatch between the substrate and films.