Structural phase stability of Se clusters in zeolites

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.

Geometry, Phase Stability, and Electronic Properties of Isolated Selenium Chains Incorporated in a Nanoporous Matrix

“…The crystallized cluster has been proved to be of trigonal form, which is stable at ambient. The crystallization temperature for bulk a -Se is about 380 K . We observed a similar crystallization process for the a -Se in the mesopores: the Raman intensity of t -Se increased and the intensity of a -Se decreased.…”

Hybrid Inorganic-Organic Perovskite Glasses

“…1b, Table 2) compared to other materials such as conventional quartz-silica (~ 911 kJ mol -1 ) 47 . This, alongside low activation energies Ea for the glass transition of ~ 20 kJ mol -1 compared to inorganics (~ 100 kJ mol -1 ) 48 , point to the greater accessibility, and processability of the liquid state, even when compared to existing MOF-glasses 46 . As competing metal reduction and ligand cyclisation processes, and (iii) the presence of tertiary amine cations, which underpins moderate electrical conductivities (10 -2 -10 -4 S m -1 ) found in the glasses.…”

“…) 47 . This, alongside low activation energies Ea for the glass transition of ~ 20 kJ mol -1 compared to inorganics (~ 100 kJ mol -1 ) 48 , point to the greater accessibility, and processability of the liquid state, even when compared to existing MOF-glasses 46 . As with examples from the zeolitic imidazolate framework family, the rare event of metallinker bond breakage leads to under-coordination of M 2+ ions in a diffusive liquid state.…”