抄録
Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for General Scientific Research (C), Fund Type: -, Overall Grant Amount: - (direct: 2500000, indirect: -)
Using a newly developed method for the studies on the dynamic of phase transitions, the following results were obtained.
(1).A molecular crystal 'Sucrose' was investigated with a pico-second pulsed laser. It was found the lifetime of the fluorescence sharply decreases as the melting point is approached. By comparing with the X-ray study, it was found that the onset of the observed shortening from a temparature about 25K below Tm was an indication of the collapsing process of the regular crystal structure into an amorphous state. This would be the first measurement of a precursor of a melting transition by light.
(2) A single crystal of ice(Ih) doped with 2-naphthol(2-C8H10(0H)) molecules was grown. The fluorescence lifetime measurements recealed that a stepwise decrease of lifetime from 5ns to 2ns occurs between 130K and 200K.The behavior was analyzed by a model which takes into account the relaxation of the proton configurations in the neighborhood of the naphthol molecules. The analysis allowed us to estimate the activation energy for the generation of L-defects in ice.
(3) A structural phase transition of a single crystal biphenyl was investigated by a similar method. The lifetime shows a minimum at the transition temperature Tc=40K, where biphenyl undergoes a second order incommensurate phase transition. In conrast to the significant change in the lifetime of the broadband fluorescence, a sharp zero-phono line at lambda=533nm was found to have a rather long lifetime without any critical temperature depenedence.
All the results confirmed that that the present method can be a sensitive probe of fluctuations associated with the phase transitions and would be able to be applied to variety of phase transitions. The results were reported, e.g.in the 8th International Meeting on Ferroelectricity and will appear in several journal(in press and submitted).