Direct measurement of mechanical properties of (Pb,La)TiO3 ferroelectric thin films using nanoindentation techniques

A procedure using nanoindentation with spherical tipped indenters is presen ted that allows separation of elastic, anelastic, and plastic contributions to the deformation of thin films. The procedure was demonstrated on a rang e of lanthanum-modified lead titanate (Pb,La)TiO3 (PTL) ferroelectric thin films. Indentation stiffness coefficients ranging from 110 to 147 GPa have been obtained depending on the microstructure and orientation of the PTL fi lms. This coefficient was equivalent to land so, can be directly compared w ith) Young's modulus of a nontextured, unpoled ceramic when films do not pr esent preferred orientation. The trends of the anelastic contribution with the thickness, structure, microstructure, and stress level at the film/subs trate interface of the films were consistent with it being produced by ferr oelastic domain wall movement. Pore compaction was a major mechanism of pla stic deformation for the PTL films. Grain size also affected plastic deform ation, probably as a consequence of its correlation with intergranular poro sity. The technique has a high spatial resolution (contact area < 10 <mu>m( 2) for the results presented here), which allowed the mechanical homogeneit y of the films to be studied and inhomogeneities to be identified from thei r mechanical response (elastic, anelastic, and plastic).