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Instabilities of Crystals and their Functional Behaviour

Title: Instabilities of Crystals and their Functional Behaviour

Speaker: Prof. Umesh Waghmare, JNCASR, Bengaluru

Date: 25th January, Wednesday, 20235:30-6:30 pm at CV Raman Hall, Transit Campus of IISER Tirupati

Abstract: Properties of a crystalline material are fundamentally determined by its electronic and atomic structure. Some crystals host instabilities that cause sharp changes in the structure with temperature or external fields while preserving their rigidity. Symmetry breaking at such a structural transition is often responsible for the emergence of the material’s technologically important functional properties. For example, applications of a ferroelectric crystal in sensors, speakers, heartbeat monitors or in memories are possible due to its functional properties of piezoelectricity and electrically switchable dipoles, which emerge from the broken inversion symmetry of the structure at a ferroelectric transition caused by an instability of a polar phonon. Functional properties of advanced materials have their roots in various such incipient instabilities. In this talk, I present First-principles theoretical approach based on fundamental laws of Physics that can be used in identifying such instabilities in crystals and development of simple effective models that capture interactions between the instabilities and external forces, enabling prediction of material specific functional behaviour of advanced materials. This approach relies on computer simulations and guides experimental efforts towards development of novel materials and devices. We illustrate it in the context of crystal instabilities that are relevant to functional properties of ferroelectric, thermoelectric and shape memory alloys, which have numerous technological applications.