Structure stability of confined bismuth sesquioxide phases – low-temperature experimental and computational studies

Several bismuth sesquioxide (Bi \(_{2}\) $_2^{}$ O \(_{3}\) $_3^{}$ ) phases (namely \(\upbeta\) $\mathrm{\beta }$ , \(\upgamma\) $\mathrm{\gamma }$ and \(\updelta\) $\mathrm{\delta }$ -like) were previously stabilized at room temperature by nanocrystallization of bismuthate glasses. Normally, a monoclinic \(\upalpha\) $\mathrm{\alpha }$ phase is the stable one at ambient conditions in polycrystalline materials. In this work, we wanted to observe if any phase transitions would occur below the room temperature for \(\upbeta\) $\mathrm{\beta }$ , \(\upgamma\) $\mathrm{\gamma }$ and \(\updelta\) $\mathrm{\delta }$ -like phases confined in a residual glassy matrix. Observations were made down to 100 K using X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). Both experimental techniques showed no traces of phase transition upon cooling to the temperature limit of our equipment. From XRD studies, the lattice parameter of the δ-like phase was determined. The values were compared to the values calculated by molecular dynamics studies of overcooled \(\updelta\) $\mathrm{\delta }$ -Bi \(_{2}\) $_2^{}$ O \(_{3}\) $_3^{}$ phase.