The state-of-the-art material contains lead (Pb) which is highly toxic and restricted by the EU RoHS directive. Moreover, very recently, a new family of electromechanically active materials has been discovered: oxygen defective ceria. Such material displays a gigantic electromechanical response with an electrostriction strain coefficient (M33) ~10−16-10−18 m2/V2, following a non-classical behavior. The governing mechanism is attributed to the rearrangement of electroactive elastic dipoles (CeCe-Vo) that rearranges the bond length under an electric field.
In my Ph.D. thesis, I fabricated highly-dense polycrystalline bulk ceria compounds (Ce1-xMxO2-δ) varying dopant type/concentration by different thermal treatments, including field-assisted sintering, cold sintering process, and conventional free sintering for room temperature electromechanical applications. Such approaches develop different microstructure with modified defect configurations at the ion-blocking barriers. Electrochemical, mechanical, microstructural, and electromechanical characterization were performed on the samples. It was found that M33 demonstrates strain saturation and non-Debye frequency relaxation depending on the extent of dopant-defect electro-steric interaction. Remarkably, neither grain size nor bulk conductivity dominated effect is observed.
My current research which proceeds since October 2020 within the DFG funded research unit “periodic low-dimensional defect structures in polar oxides” is to investigate the correlation of point defects, domain structure, charge transport, and electromechanical properties of the model system lithium niobite-tantalate (LiNb1-xTaxO3, LNT). The objective of this work is to enhance the electromechanical quality factor of resonant devices, temperature range, long-term stability in harsh operating conditions as well as to develop a device for contactless measurement for acoustic losses.
Figure: Atomistic mechanism of non-classical electrostriction in ceria
Dr. Ahsanul Kabir
Technical University of Clausthal
Institute of Energy Research and Physical Technologies
38640 Goslar, Germany