Dielectric and transverse piezoelectric characterization of sol-gel derived Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (70/30) films with (100) and (111) textures

Highly (100) and (111) oriented Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (70/30) films were deposited on Pt(111)-passivated silicon substrates using a modified sol-gel process. In both cases, the degree of preferred orientation did not change with film thickness from 0.56 μm to 1.5 μm. The room temperature dielectric constants for the (100)-oriented films were 2100-2650, while those for the (111) oriented films were 1900-2350. In both cases tan δ was less than 0.03. It was found that the piezoelectric coefficient (d₃₁) of the PMN-PT films increased with increasing film thickness. The d₃₁ coefficient of highly (100) oriented PMN-PT films poled for 5 minutes at 85 kV/cm were found to range from -45 to -86 pC/N assuming a Young's modulus of 35 GPa. Highly (100) oriented PMN-PT films showed larger piezoelectric coefficients than (111) oriented films. Results on aging of the piezoelectric coefficients for the differently oriented films are also presented.