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ELECTROACTIVE CERAMICS FOR ENERGY APPLICATIONS

We are developing new environmentally friendly Pb-free electroactive ceramics for several energy related applications. Our research is driven by two principal objectives: (A) developing ceramics with large pyroelectric coefficient for thermal energy harvesting and electrocaloric cooling, and (B) developing ceramics with large dielectric constants for high density capacitive energy storage applications. Our primary interest is in a family of compositionally disordered polar oxides called relaxors. We are exploring the inter-relationships between materials composition and short-range atomic structure and dynamics, based on which high performance relaxors can be developed for the above applications

CHARACTERIZATION OF LOCAL ATOMIC STRUCTURE AND DYNAMICS

For many electroactive oxides, it is the local deviations from the spatially averaged crystal structures that are important for many of their functional properties. Such local structural deviations cannot be measured from traditional analysis of Bragg diffraction peaks alone. We are using advanced characterization techniques, such as instantaneous and dynamic pair distribution function analysis, measurement of single crystal diffuse scattering, and inelastic scattering, to understand how the atomic structures in disordered oxides, such as relaxors, are correlated in space and time. Such multi scale structural insights are used to guide development of new materials.

DEFECT CHEMISTRY AND TEXTURE IN THIN FILM OXIDES

Controlled synthesis of thin films constitutes an important step towards transitioning of new materials into devices. We are using various physical vapour deposition techniques, such as pulsed laser deposition (PLD) and sputtering, to grow thin films oxides of complex compositions. We are exploring how the different materials aspects such as ionic defects and crystallographic texture can be engineered in thin film oxides to boost their performance in applications such as capacitive energy storage or pyroelectric energy harvesting. For example, we recently demonstrated achieving record combination of energy density, efficiency and thermal stability in Pb-free relaxor thin films by combining certain ionic defect complexes and (110) growth textur

POLYMER FERROELECTRICS

Polymer ferroelectrics have gained much attention due to their higher breakdown strength and greater flexibility as compared to ferroelectric ceramics. A particularly distinct characteristic of polymeric ferroelectrics is their semi-crystalline nature, whereby different configurations of monomers are arranged along long C chain within nanoscale lamellae. The development of precise structure-property relationships which govern the functionalities of polymer ferroelectrics is still in its early stages. We are using advanced x-ray and neutron scattering techniques to understand the structural aspects of phase transition and electric-field-induced response in PVDF-based polymer ferroelectrics. We are also exploring different post-processing modifications of ferroelectric polymer thin films to engineer certain phase microstructure to obtain desired properties.

MICROSCOPIC MODELS FOR NEW LEAD-FREE FERROELECTRICS

Piezoelectric ceramics are used in precision actuators, energy harvesting, biomedical instruments and sensors. Although commercial  piezoceramics are mostly made with Pb-based compositions, concerns about toxicity of Pb has led to extensive research into Pb-free piezoceramics over last 15 years. Subsequent commercial implementation of many of the new Pb-free piezoceramics, in both bulk and thin film forms, will depend on improvement of their reliability and long-term stability, for which detailed microscopic insights are necessary. We are using results from in situ diffraction experiments to develop detailed micromechanical models for field-induced response in new Pb-free piezoceramics.