No abstract

No abstract

No abstract

The effect of confinement on the structural phase of Se clusters in zeolites (LTA and FAU) has been studied in the temperature range of 300 ∼ 550 K by Raman scattering and differential scanning calorimetry. It has been found in Raman spectra that the structural unit and phase stability of Se clusters are greatly affected by the geometrical restriction in the zeolites. No clear phase transformation was observed by DSC measurements for Se clusters in LTA zeolites, while Se clusters in FAU zeolites exhibit a distinct endothermic peak which is ascribed to a glass transition. The glass transition temperature of amorphous Se (320 K) is remarkably elevated when Se rings/chains are incorporated in FAU zeolites; the higher glass transition temperature for the smaller window diameter of zeolites. We have also found that the activation energy for the glass transition is decreased drastically in the zeolites; the smaller activation energy for the smaller window size. The observations imply that the kinetics of the structural relaxation at the glass transition of Se is significantly influenced by the absence of inter-cluster interaction and that the thermokinetic dimension becomes lower owing to the geometrical restriction in the zeolites.

We have studied the electronic and vibrational properties of CdS and Se clusters in zeolites by Raman scattering and photoluminescence measurements. CdS clusters were formed photochemically through the dissociation of S 8 molecules in A and X types of Cd 2+-exchanged zeolites by laser irradiation, while CdSe clusters were not successfully produced in the same manner. The 1LO mode of CdS at 300 cm −1 shifts to lower frequencies in the zeolites in comparison with that of bulk CdS , indicating the effect of phonon confinement. Se clusters incorporated into zeolites with different pore sizes (3A, 4A, 5A, and 13X) exhibit strong dependence of the structural phase stability and the structural unit on the geometrical constraints of zeolites.