Defence Brenda Carreño Jiménez: "KNN-based piezoelectric materials: Characterization and engineering approaches"

Promotors: 1^st promotor: Prof. Monica Acuautla Meneses, 2^nd promotor: Prof. Jacquelien Scherpen, co-promotor: Dr. Rigoberto López Juárez

Abstract: Piezoelectric materials are known for their ability to convert mechanical energy into electrical energy, and vice versa. This makes them crucial components in a variety of applications, including ultrasonic devices, micro- and nanopositioning systems, and micro generators. One of the most widely studied materials are lead-free ceramics based on (K,Na)NbO3, despite the ongoing challenges in enhancing their performance. This thesis therefore focuses on (K,Na,Li)(Nb,Sb)O3 ceramics doped with BaZrO3 and (Ba,Ca)ZrO3 as an alternative of improving the piezoelectric and ferroelectric properties of undoped (K,Na)NbO3 ceramics. This thesis undertook an extensive structural, microstructural and electrical characterisation of these ceramics, which have been used to evaluate their performance as sensors or energy harvesters under different electromechanical simulations by finite element analysis. In addition, three engineering applications have been investigated experimentally: 1) As sensors, subjected to various mechanical loads to evaluate output voltage and repeatability. 2) As actuators, to determine ferroelectric properties and deformation under an applied electric field (including a study of fatigue resistance). 3) As energy harvesters, using cantilevers under vibration to collect generated energy. On the other hand, (K,Na,Li)(Nb,Sb)O3-(Ba,Ca)ZrO3 thin films have been fabricated and characterised. This approach is driven by the growing need to miniaturise electronic components. Initial results demonstrate promising piezoelectric and ferroelectric behaviour at the microscale, highlighting the potential of (K,Na,Li)(Nb,Sb)O3-based thin films, fabricated optimally and evaluated for reliability. This research provides insights into the use of dopants, fabrication design and engineering strategies for (K,Na,Li)(Nb,Sb)O3-based piezoelectric ceramics, with the goal of guiding their future applications.

Dissertation