Projects / Programmes
DESIGNING FUNCTIONALITY OF LEAD-FREE FERROELECTRICS THROUGH DOMAIN WALL ENGINEERING
| Code |
Science |
Field |
Subfield |
| 2.04.01 |
Engineering sciences and technologies |
Materials science and technology |
Inorganic nonmetallic materials |
| Code |
Science |
Field |
| 2.05 |
Engineering and Technology |
Materials engineering |
lead-free ferroelectrics, domain wall, structure, microscopy
Researchers (12)
Organisations (2)
Abstract
Ferroelectrics, as a subgroup of piezoelectric materials, are very important to the electronics, automobile, and other industries, making them worth billions of dollars annually. The dominant ferroelectric materials are based on lead zirconate titanate – PZT. These materials contain lead, which, due to its special electronic configuration, is responsible for the materials’ good ferroelectric properties. However, the toxicity of lead during mining, manufacturing and disposal presents a significant ecological problem. The goal to replace PZT has only been partially achieved; therefore, the use of lead in ferroelectric devices has been exempted from EU restrictions of the use of hazardous substances legislation until 2021. These exemptions are reviewed periodically and once satisfactory alternatives to PZT are found, the exemptions will be lifted (MRS Bull. 43, 2018). Until now, the best lead-free material candidates are based on (K,Na)NbO3, BaTiO3, (Na,Bi)TiO3 and BiFeO3, the properties of which were mainly designed by bulk chemical modifications. These empirical approaches to finding new lead-free materials have not been totally successful. In the project we propose to design the functionality of lead-free ferroelectrics by fine tuning the nm-sized local features known as domain walls (DWs), which crucially influence the macroscopic properties. DWs are the interfaces that separate two regions of uniform polarization in ferroelectric materials, they form along various crystallographic directions at different length-scales, can accumulate different ionic or electronic point defects, with all of these influencing the DW nucleation and mobility. Typically, the ferroelectric DW thickness ranges from 1 nm to 10 nm, meaning that the detailed structure of the DWs can be experimentally studied only by atomically resolved analytical methods. Moreover, only recent technological improvements achieved by in-situ electron microscopy techniques allow the real-time observation of the dynamic responses of DWs under external stimuli down to the atomic scale. Consequently, the DWs’ structural details at the nano and atomic levels, especially in correlation to the DWs mobility under an applied electric field, are unclear, hindering our fundamental understanding of the influence of DWs on the macroscopic ferroelectric properties and thus the engineering of lead-free ferroelectric materials. In the proposed project, we will close this gap. In the project we propose to design the functionality of (K,Na)NbO3 KNN-based materials, relevant for medical applications and BiFeO3 BFO-based materials, relevant for high-temperature applications, through domain-wall engineering with the support of first-principles calculations and advanced and innovative characterization methods down to the atomic level. The objectives of the project are (i) designing DWs in KNN- and BFO-based materials by controlling of type and concentration of defects through different material processing conditions (temperature, atmosphere, cooling rates, and dopants), (ii) identifying the pinning defects that are affecting the DW mobility by changing the temperature and/or electric field and (iii) finding a lead-free material with enhanced extrinsic contributions by correlating the structural features and local dynamics of DWs with the macroscopic material response. The project is based on our recent study published in the Nature Materials (Nat. Mat. 16, 2017), where we established that the segregating electronic defects at DWs effect the DWs’ local conductivity and consequently the macroscopic response of BFO. The project is divided into three inter-related work packages: Material engineering through DWs; DW characterisation, supported by ab-initio structure calculations and, the DW dynamics. The equipment for the realization of the project is available at the Jozef Stefan Institute and at the National Institute of Chemistry, which is a partner institute.
