Naslov
Monte-Carlo simulation of paramagnetic probe in KDP-type ferroelectrics

Autori
Merunka, Dalibor ; Rakvin Boris

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Advanced Methods in Electron Paramagnetic Resonance Spectroscopy / - Caorle : European Federation of EPR Groups, 1999, 31-31

Skup
Summer School:Advanced Methods in Electron Paramagnetic Resonance Spectroscopy

Mjesto i datum
Caorle, Italija, 12.09.1999. - 19.09.1999

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
ferroelectrics;isotope effect;EPR

Sažetak
The KH2PO4-types, KDP, of ferroelectrics are characterized with a large isotopic effect on the critical temperature, Tc, when H is replaced with D. A KDP crystal exhibits the ferroelectric phase transition on Tc=122 K, while KD2PO4, DKDP, on Tc=220 K. Until now, the mechanism of the phase transition and the origin of such large isotopic effect have not been satisfactory explained. Paramagnetic centers such as AsO44-, SeO43- and CrO44- were implemented in these crystals as probes for the studies of low-frequency lattice dynamics. The EPR detected frequencies (107-1010 Hz) are much lower than frequencies of lattice modes in original crystal. This local dynamics of crystal around the probe includes hopping between two configurations and can be described with the correlation time, , which exhibits simple Arrhenius behavior =0exp(E/kT). Generally,  shows an isotopic effect such that probes in deuterated crystals exhibit larger activation energy E and smaller preexponential factor 0. Recently, Sugimoto and Ikeda proposed a model for KDP [1] based on strong coupling of the electric dipole moment of the tetrahedron to surrounding protons (deuterons) and qualitatively explained the large isotopic effect in KDP. This model was modified and by employing Monte Carlo simulation a better agreement with experimental value for Tc in DKDP was obtained. A paramagnetic probe is described in this modified model as a dipole having one of parameters different than the original one. This parameter is related to deformation energy when the dipole moment of tetrahedron along c-axis is induced. Monte Carlo simulation of such probe in the paraelectric phase of KDP and DKDP system were performed. It is found that c-component of the dipole of probe has a double-well effective potential. The energy of the barrier is temperature dependent and has larger values for DKDP than for KDP lattice. The thermally activated hopping of the probe across the barrier in these potentials were analyzed and results were compared with the experiment.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

POVEZANOST RADA