Piezoelectric materials convert mechanical stress into electrical voltage and vice versa. As such, they form a very important class of functional materials which are pivotal to “smart” technologies including biomedical devices, ultrasensitive sensing, sonars and equipment for scientific research such as the atomic force microscope (AFM).

For decades, the most widely used piezoelectric has been a solid solution between PbTiO3 and PbZrO3 perovskites, commonly called PZT. However, due to the toxicity of lead, the use of PZT-based materials is more and more restricted in many countries. Despite intense investigations carried out to find lead-free alternatives [1][2], the piezoelectric performances of PZT remain unbeaten.

Recently, it has been shown that Ba(Ti0.8Zr0.2)O3-(Ba0.7Ca0.3)TiO3 solid solution (in short BCTZ) is a very promising contestant as it exhibits a very large piezoelectric response [3]. It has been soon recognized that the phase diagram and instabilities of BCTZ and thus the origin of the exceptional response in BCTZ appears to be fundamentally different to that of PZT. However, the theoretical framework for explaining the unconventional piezoelectric response of these systems is still in its infancy. Gaining the understanding of this original mechanism is crucial not only to assess further the potential of BCTZ but, more importantly, to achieve control of the piezoelectric response towards the design of other new lead-free and high-response piezoelectrics.

This PhD project will focus on computer modeling techniques for investigations of structural and piezoelectrical properties of BCTZ. In Liège, first principles DFT calculations of compositional and pressure effects will be performed. The results of these calculations will be used in Bordeaux for the development of phenomenological models, focusing on competition between different phases and emergence of multidomain states. Another important component are calculation of the piezoelectric response, polarization dynamics, and fluctuation effects, with specific attention on interaction between polar and antiferro-distortive instabilities. A secondment at industry partner FEI will be devoted to advanced 3D visualization and analysis of BCTZ properties. The project will interact with experimental project 2015-06.
[1] Properties of epitaxial films made of relaxor ferroelectrics. S. Prosandeev, D. Wang and L. Bellaiche, Phys. Rev. Lett. 111, 247602 (2013).
[2] Thermotropic phase boundaries in classic ferroelectrics. T.T.A. Lummen et al., Nature Comm. 5, 3172 (2014).
[3] Large Piezoelectric Effect in Pb-Free Ceramics. W. Liu and X. Ren, Phys. Rev. Lett. 103, 257602 (2009)

Project Partners

Institute for Condensed Matter Chemistry Bordeaux, France: phenomenological modeling

Department of Materials Physics, University Liège, Belgium: DFT calculations

Industry Partner: FEI, France: 3D visualisation

Host Country (employment): France

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