Enhancement of Piezoelectric\nProperties in a Narrow\nCerium Doping Range of Ba<sub>1–<i>x</i></sub>Ca<sub><i>x</i></sub>Ti<sub>1–<i>y</i></sub>Zr<sub><i>y</i>&

Lead-free materials based on the (Ba,Ca)(Zr,Ti)O<sub>3</sub> (BCZT)\nsystem exhibit excellent electromechanical properties that can be\nstrongly modified by small amounts of dopants. Here, we use a combinatorial\nstrategy to unravel the influence of aliovalent doping with Ce on\ndielectric and piezoelectric properties of BCTZ. We synthesize and\ncharacterize a single BCTZ thin film with a composition gradient from\nundoped to 0.2 mol % cerium doping. The cerium doping increases the\npiezoelectric coefficient from 42.3 ± 2.9 pm V<sup>–1</sup> (undoped) to 63.0 ± 2.4 pm V<sup>–1</sup> for 0.06 Ce-mol\n%, and then decreases to 38.4 ± 1.3 pm V <sup>–1</sup> for the maximum amount of cerium (0.2 mol %). An investigation of\nsubcoercive field nonlinearities reveals that these variations are\nnot only induced by changes in dynamics and densities of domain walls.\nThe results highlight the advantage of combinatorial techniques to\nidentify ideal compositions for applications without synthesizing\na high number of samples with unavoidable sample-to-sample variations.