Grain to grain heterogenities in PbZrTiO$_3$ thin film as probed by in-situ biasing XRD
Résumé
Piezoelectric thin-films are those which generate mechanical strain in response to applied electric field and they are used for a wide range of technological applications. The case of polycrystalline thin films is particularly complex and delicate to model. A better understanding of the intergranular responses is necessary to evaluate the intergranular constraint and the anisotropic responses of individual grains [1]. However, this problem is sparsely experimentally documented due to the lack of adequate methods. Here, the behavior of a ten of single grains of Lead Zirconate Titanate (Pb(Zr$_x$, Ti1$_{-x}$)O$_3$) has been evaluated thanks to the in-situ biasing X-ray Diffraction (XRD) technique [2] using a synchrotron source and a sub-micronic X-ray beam. A small capacitor has been biased with DC voltage between zero and ± 20V and at each step of bias a set of spotty Debye rings has been recorded. By selecting an appropriate region of interest, the evolution of a single grain peak can be extracted. The fine analysis of (200) pseudo-cubic peak allows to separate the evolution of different parameters of a/c tetragonal and rhombohedral domains during the electrical biasing. Finally, through the calculation of the center of gravity of the peaks, the effective piezoelectric coefficient ($d_{33,eff}$) was deduced which shows a heterogeneity between different grains. This research contributes to a better understanding of the local behaviors in piezo/ferroelectric polycrystalline films and in the improvement of their performance for different applications.