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PGI-1 Talk: Dr. Sagar Sarkar

Doping a dipole into an incipient ferroelectric: route to relaxor ferroelectrics

18 Sep 2019 11:30
Seminar room N-142

Indian Institute of Technology Kharagpur


In a ferroelectric material, microscopic dipole moments are formed due to cation displacements from their ideal positions in the paraelectric structure. The ordering of such microscopic dipoles in a material may or may not take place leading to ferroelectric properties. On the other hand, there are materials which are on the brinkof a ferroelectric transition, where the dipolar order is being suppressed by quantum fluctuations. Usual examples of ferroelectrics are d0 materials i.e. those which have an empty d shell. This has been an empirical principle being used to roughly identify materials which would be ferroelectric.

While not all d0 materials are ferroelectric, it has been seen that several of them could be identified as incipient ferroelectrics, where there is no ferroelectric order down to low temperatures. TiO2 is one such example. In such materials, a small perturbation could drive the system ferroelectric. In this work using ab-initio density functional theory calculations, we explore doping a Nb-Cr pair in TiO2 as a route to drive it ferroelectric. Nb and Cr go into the 5+ and 3+ valence states and therefore behave like a dipole.

Analogous to dilute magnetic semiconductors, where doping small concentrations of magnetic atoms in otherwise non-magnetic materials drives the system magnetic, here, the introduction of the dipole is shown to polarize regions in the vicinity of the dopant. Ferroelectricity is therefore found to be stabilized. While this mechanism is indeed found to work at low concentration Nb-Cr doping, at higher doping concentrations a clustering of the dopant atoms is found to destroy long-range ferroelectric order.


Dr. Manuel dos Santos Dias
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