Sr-fresnoite surface crystallisation in a 2SrO·TiO2·2.75 SiO2 glass studied by EBSD

Abstract

A glass of the composition 2SrO?TiO 2 ?2.75SiO 2 was melted. Cooled samples were polished and thermally annealed at 970 uC for 10 min to 20 h to achieve surface crystallisation of Sr 2 TiSi 2 O 8 fresnoite. At the surface, the crystals were immediately oriented with their crystallographic c-axes perpendicular to the surface. Crystal growth occurred in the form of similarly oriented structures. Very homogeneous structures were also observed but they fray into areas of higher orientation diversity at some distance from the surface. The crystallised areas were highly permeated by nanoscale inclusions of residual glass. Kinetic selection occurs and leads to a preferred orientation with the crystallographic c-axis tilted by about 43 ¡ 5u from the surface normal after about 300 mm. Crystal growth is not governed by the fastest growing crystallographic direction or the formation of a diffusion barrier, but rather by the ability to circumvent the residual glass.

The influence of TiO 2 and ZrO 2 on microstructure and crystallization behavior of CRT glass

“…The lack of bulk crystallization allowed us to conclude that nucleation occurred solely on the surfaces. This seems to be in contradiction to the crystallization of BTS reported in [19], but comparable with data shown by W. Wisniewski for the surface crystallization of Sr 2 TiSi 2 O 8 fresnoite [39][40][41]. The EDX spectra of samples support the above XRD results.…”

Oriented Nucleation of both Ge-Fresnoite and Benitoite/BaGe4O9 during the Surface Crystallisation of Glass Studied by Electron Backscatter Diffraction

“…also observed in STS containing glass-ceramics3839. Polarization micrographs of cross sections have been published24 and indicate a strong optical anisotropy.…”

“…Samples annealed at only 695 and 700 °C have been proposed to show XRD-patterns similar to the powder pattern16 and it was concluded that the crystalline phase is not oriented at the surface161724. 001 textures have also been indicated by XRD in BTS4041 and STS38 glass-ceramics, but the application of EBSD showed that the topmost layer shows a different orientation in the case of BTS40 which is affected by the annealing temperature40. Actually, the analysis of surface crystallized STS from the composition STS+0.45 SiO 2 provided the first case where the texture detected at the immediate surface also prevailed during growth39 while a texture change is observed more often33404243.…”

“…The application of electron backscatter diffraction (EBSD) to the surface crystallization of glass-ceramics containing BTS4041 and STS383942 has significantly altered the understanding of occurring crystal orientations and textures in these systems. For example, the observation of oriented nucleation in these glass-ceramics3839404142, also observed e.g.…”

Analysis of the cordierite X-phase and phase transformation by electron backscatter diffraction (EBSD)

“…with piezoelectric properties in the case of fresnoite [1,2]. The main mystery of this process is the surface nucleation itself, which has recently been realized to be more complicated than previously thought as oriented nucleation has been shown to occur in a number of surface crystallizing glass systems [1][2][3][4][5][6].…”