[seminar] Seminar na IF-u u četvrtak 11.5.2017. u 15:00h - dr. B. Gorshunov, Stuttgart

[Damir Staresinic]

Institut za fiziku, Bijenička cesta 46, 

predavaonica u zgradi Mladen Paić četvrtak, 11. svibnja 2017., u 15:00 sati 
Single-particle excitations and incipient ferroelectricity of nanoconfined water molecules 
dr. Boris P. Gorshunov 
Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region, 141700 Russia 
A. M. Prokhorov General Physics Institute, RAS, Moscow, 119991 Russia 
1. Physikalisches Institut, Universität Stuttgart, 70569 Stuttgart, Germany 







By using radiofrequency and terahertz spectroscopy (frequencies 1 Hz to 10 14 Hz), at temperatures 0.3 K to 300 K, we have studied excitations of an ensemble of single water molecules that are caged within subnano-sized (0.5 nm) voids formed by ions of the beryl (Be 3 Al 2 Si 6 O 18 ) crystal lattice. Measurements on dehydrated samples allow to extract absorption lines caused exclusively by water molecules, on the background of phonons resonances. In the infrared range, well-known H 2 O intramolelular modes ν 1 (symmetric elongation), ν 2 (bending), and ν 3 (asymmetric elongation) of the H 2 O are observed. Spectra recorded below 1000 cm −1 reveal rich set of highly anisotropic absorption bands of the low-energy response of caged H 2 O molecules. Performing the DFT analysis we can assign the bands to librational and translational vibrations of separate water molecules that are weakly (van der Waals) coupled to the cages’ ldquo;walls”. At terahertz frequencies, we detect clear signs of emerging incipient ferroelectric phase within water molecules that are coupled via long-range dipole-dipole forces, with the shorter-range hydrogen bonds "switched off" due to large (4 to 9 Angstroms) intermolecular spacing. On cooling from room temperature, the static permittivity increases according to the Curie-Weiss law as a collective ferroelectric soft mode develops in the terahertz frequency range. At temperatures below 10 K, quantum fluctuations eventually suppress the ferroelectric phase transition and lead to a saturation of the soft mode parameters and of the static permittivity. We describe our results within the framework of a mean-field microscopic model that considers rotational and librational motions of interacting water molecular dipoles in a six-well potential. 




Voditelji seminara IF-a: [ mailto:natasav at ifs.hr | Nataša Vujičić ] i [ mailto:damirs at ifs.hr | Damir Starešinić ] 

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