Background, Motivation and Objective Lead containing high performance PZT piezoelectric ceramics used in ultrasound transducers will soon be banned according to the European RoHS directive. Alternative lead-free material should have the highest possible coupling factors (kij, kt, kp) and Curie temperature (TC). ABO3-type perovskite oxides exhibit a wide range of physical properties defined by the fine balance of competing interactions and are stable against a large number of substitutions. BT-type titanates are already commercially exploited as good alternatives to PZT. The compound 0.5BaZr0.15Ti0.85-0.5Ba0.7Ca0.3TiO3 (50BCTZ with TC = 90°C, d33 ~ 490 pC/N comparable to soft PZT) was thus used to produce the first lead-free ultrasound probe. Substitution on A or B site at low concentrations influences significantly the piezoelectric properties and the TC. Statement of Contribution/Methods The extreme sensitivity of the properties to cationic content requires multi-doping fine screening that we achieve via high throughput synthesis and characterisations. A systematic and statistical exploration of (Ce,Y) co-doped 50BCTZ phase diagrams is done in thin films libraries. A range of structural, chemical and physical local characterisations (-XRD, WDS, STEM, DBLI, P(E) and IS vs T with Rayleigh analysis) to relate composition, microstructure and physical properties. Results/Discussion Co-doped (Ce,Y)-50BCTZ libraries are currently investigated and will be discussed. Focusing on Ce, we showed that going from 0% to 0.2% in doping modifies the lattice parameter, reduces the remnant polarisation, and shifts the maximum permittivity temperature (Tmax) value. For compositions with Tmax close to room temperature, we measured a 25% enhancement of room-temperature d33 piezoelectric coefficient. We then use dielectric spectroscopy coupled with the Rayleigh analysis to identify the contribution of domain wall motion to the ferroelectric response of the films, as a function of temperature. We observed residual ferroelectricity above Tmax, similar to what has been observed for (Ba,Sr)TiO3. In addition, measurement of the third harmonic dielectric response revealed the evolution from a conventional ferroelectric character to a relaxor one with increasing temperature. A peculiar phase angle of the third harmonic, which consists of −180◦ → −225◦ → +45◦ → 0◦, instead of the −180◦ → −90◦ → 0◦ found for relaxors, was also observed in several samples and tentatively attributed to changes in the correlations between polar nanoregions.