Crystallization of BaF2 from droplets of phase separated glass – evidence of a core–shell structure by ASAXS. Issue 30 (16th July 2020)

• Record Type: Journal Article
• Authors: Hoell, Armin; Raghuwanshi, Vikram Singh; Bocker, Christian; Herrmann, Andreas; Rüssel, Christian; Höche, Thomas
• Is Part Of: CrystEngComm. Volume 22:Issue 30(2020)
• Page Start: 5031
• Page End: 5039
• Publication Date: 2020-07-16
• Subjects: Crystals -- Periodicals; Crystal growth -- Periodicals; Crystallography -- Periodicals; Cristaux -- Périodiques; Cristaux -- Croissance -- Périodiques; Cristallographie -- Périodiques; 548
• DOI: 10.1039/c9ce02003a
• Languages: English
• ISSNs: 1466-8033

Abstract

Abstract : Glasses with the mol% compositions 1.88 Na2 O·15.04 K2 O·7.52 Al2 O3 ·69.56 SiO2 ·6.00 BaF2 and 1.88 Na2 O·15.03 K2 O·7.52 Al2 O3 ·69.52 SiO2 ·6.00 BaF2 ·0.05 SmF3 were studied using X-ray diffraction, transmission electron microscopy, and anomalous small-angle X-ray scattering. Abstract : Glasses with the mol% compositions 1.88 Na2 O·15.04 K2 O·7.52 Al2 O3 ·69.56 SiO2 ·6.00 BaF2 and 1.88 Na2 O·15.03 K2 O·7.52 Al2 O3 ·69.52 SiO2 ·6.00 BaF2 ·0.05 SmF3 were studied using X-ray diffraction, transmission electron microscopy, and anomalous small-angle X-ray scattering (ASAXS). While the glass doped with samarium showed liquid/liquid phase separation of droplets with sizes of around 100 nm, the glass without samarium did not. The samples were annealed at 580 °C or at 600 °C which led to the crystallization of cubic BaF2 . The X-ray diffraction patterns showed strongly broadened lines. Hence, the BaF2 crystals possess sizes in the nm range. ASAXS gave evidence of a core shell structure. In agreement with earlier studies, it is assumed that the shell acts as a diffusion barrier that hinders crystal growth. Surprisingly, the cores and shells from the crystallization of the homogeneous glass and from the second glass, which is Sm-doped and shows liquid/liquid phase separation, both possess similar dimensions, even though the origin of the barrier is very different. The doped samples show long luminescence lifetimes of nearly 5 ms at a wavelength of 600 nm, which is nearly as long as those in fluoride phosphate glasses.