Electronic and Vibrational Structure of Ferroelectric Materials * CANCELLED *
|Start date||08-06-2015 10:00|
|Finish date||08-06-2015 11:00|
|Location||Room 500 - 501, Central Building|
|Speaker's name||Ali AL-ZEIN|
|Speaker's institute||ESRF, Grenoble, France|
|Contact name||Claudine Roméro|
|Host name||Pieter Glatzel|
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Ferroelectric materials exhibit a net spontaneous polarization that can be reversed by applying an external electric field. Ferroelectrics belonging to the family of complex perovskites are promising materials for piezoelectric and electro-optic devices, condensers, etc. . Normal ferroelectrics such as barium titanate BaTiO3 and lead titanate PbTiO3 are characterized by a Curie temperature TC which corresponds to the maximum of the dielectric constant and to a well-defined phase transition from ferroelectric to paraelectric state. In the contrary, relaxors are characterized by diffuse phase transitions and dielectric dispersion, which distinguishes them from normal ferroelectrics with sharp peak in the dielectric response. Although the true origin of the relaxor behavior remains controversial it is generally admitted that their reported outstanding properties are governed by a peculiar microstructure, which consists of nanoscale polar regions, a reason for which relaxor ferroelectrics are often called ‘‘dirty ferroelectrics’’ .
In my talk, I will give a brief introduction about normal ferroelectrics in comparison with relaxors and I will show some recent examples about the electronic and vibrational structure of prototypical ferroelectric materials such as BaTiO3, strontium titanate SrTiO3  and lead magnesium niobate PbMg1/3Nb2/3O3 (PMN) using resonant inelastic X-ray (RIXS) scattering and hyper-Raman scattering (HRS). In particular, I will present RIXS data concerning the charge transfer excitations of BTO in function of temperature and HRS data to probe the soft mode of PMN relaxor [4,5].
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 A. Al-Zein, J. Hlinka, J. Rouquette, and B. Hehlen, Phys. Rev. Lett. 105, 017601(2010).
 B. Hehlen, A. Amouri, A. Al-Zein, and H. Khemakhem, JPCM 26, 015401 (2014).
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