Keywords: Lead free piezoelectric, Thin films, Sputtering, Ceramics, SPS sintering
Piezoelectric materials, which allow direct conversion of mechanical energy into electrical energy, are integrated in numerous technologies including transductors (for sonars, medical diagnostics, energy harvesting…), sensors and actuators. The performances of miniaturized devices are directly related to the properties of the piezoelectric materials deposited in form of thin films. European directives on hazardous substances (REACH and RoHS) currently impose finding alternative solutions to the most often used piezoelectric material in industry, PbZrx Ti1-x O3 (PZT), containing 60% lead mass.
The solid solution K1-x Nax NbO3 (KNN) represents a potential candidate (attractive electromechanical performances compared to PZT along with higher operating temperatures) with structural/physical properties that can be fine tuned by controlling composition.
This PhD thesis aims at exploring the NaNbO3 -KNbO3 phase diagram in thin films, through the development of mutli-target magnetron co-sputtering process followed by systematic characterizations of the chemical, structural and physical properties of thin films. A comparative study with bulk ceramics on compositions of interest is also planned.
- Environment and methods :
This thesis will be carried out at the GREMAN laboratory at Tours University (http://greman.univ-tours.fr/ ) in the pole “Synthesis of Materials” Blois, France. The PhD student will use the recent installation of a multi-target RF magnetron sputtering reactor. Various processes will be explored in order to tailor the stoichiometry and structure in thin films. Structural (XRD, Raman/IR Spectroscopies, FEG-SEM, AFM), chemical (EDX) and physical ((di/piézo/ferro)-electric measurements) characterizations will be made at GREMAN and CERTeM (http://certem.univ-tours.fr/ ) to correlate deposition conditions and thin film properties. Ceramic sintering will be carried out by Spark Plasma Sintering (SPS). Additional characterizations will be done in collaboration with THALES company.