On the issue of textured crystallization of Ba(NO₃)₂ in mesoporous SiO₂: Raman spectroscopy and lattice dynamics analysis

Journal
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy  
Volume
275
Article Number
121157
Citation
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy 275: 121157 (2022-07-05)
Publisher DOI
10.1016/j.saa.2022.121157
Scopus ID
2-s2.0-85126611247
The lattice dynamics of preferentially aligned nanocrystals formed upon drying of aqueous Ba(NO3)2 solutions in a mesoporous silica glass traversed by tubular pores of approximately 12 nm are explored by Raman scattering. To interpret the experiments on the confined nanocrystals polarized Raman spectra of bulk single crystals and X-ray diffraction experiments are also performed. Since a cubic symmetry is inherent to Ba(NO3)2, a special Raman scattering geometry was utilized to separate the phonon modes of Ag and Eg species. Combining group-theory analysis and ab initio lattice dynamics calculations a full interpretation of all Raman lines of the bulk single crystal is achieved. Apart from a small confinement-induced line broadening, the peak positions and normalized peak intensities of the Raman spectra of the nanoconfined and macroscopic crystals are identical. Interestingly, the Raman scattering experiment indicates the existence of comparatively large, ∼10–20 μm, single-crystalline regions of Ba(NO3)2 embedded in the porous host, near three orders of magnitude larger than the average size of single nanopores. This is contrast to the initial assumption of non-interconnected pores. It rather indicates an inter-pore propagation of the crystallization front, presumably via microporosity in the pore walls.
Subjects
Ba(NO ) 3 2
Confinement effect
Density functional theory
Phonon
Porous SiO 2
Raman scattering
X-ray diffraction
DDC Class
530: Physik