Oriented growth of a β-quartz solid solution from a MgO–Al 2 O 3 –SiO 2 glass coated by a sol–gel ZrO 2 layer

Seidel

Patzig

et al. 2017

Sci Rep

Self Cite

The crystallization behavior of a glass with the composition 54.7 SiO2·10.9 Al2O3·15.0 MgO·3.4 ZrO2·16.0 Y2O3 is studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) including electron backscatter diffraction (EBSD) and (scanning) transmission electron microscopy [(S)TEM] including energy-dispersive X-ray spectrometry (EDXS). This glass shows the sole surface crystallization of four different yttrium silicates of the composition Y2Si2O7 (YS). The almost simultaneous but independent nucleation of α-, β-, δ-, and ε-YS at the surface is followed by growth into the bulk, where ε-YS quickly dominates a first crystallized layer. An accumulation of Mg at the growth front probably triggers a secondary nucleation of β-YS, which forms a thin compact layer before fragmenting into a highly oriented layer of fine grained crystals occupying the remaining bulk. The residual glass between the YS growth structures allows the crystallization of indialite, yttrium stabilized ZrO2 (Y-ZrO2) and very probably μ-cordierite during cooling. Hence, this glass basically shows the inverted order of crystallization observed in other magnesium yttrium alumosilicate glasses containing less Y2O3. An epitaxial relationship between Y-ZrO2 and ε-YS is proven and multiple twinning relationships occur in the YS phases.

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Surface Crystallization of a MgO/Y2O3/SiO2/Al2O3/ZrO2 Glass: Growth of an Oriented β-Y2Si2O7 Layer and Epitaxial ZrO2

Seidel

Patzig

et al. 2017

Sci Rep

Self Cite

“…By contrast, the crystallisation of stuffed β-quartz did not lead to piezoelectric samples 33 . It should be noted that both fresnoite and β-quartz are not ferroelectric and hence cannot be poled.…”

Section: Resultsmentioning

confidence: 84%

Growing Oriented Layers of Bi4Ti3O12 in Bi2O3/TiO2/SiO2/Nd2O3/Al2O3 Glass-Ceramics by Melt Quenching

Slavov

Rüssel

et al. 2018

Sci Rep

Self Cite

A glass melt with the composition 24Bi2O3/40TiO2/10SiO2/10Nd2O3/16 Al2O3 was prepared and rapidly quenched between two copper blocks (sample A). A part of this glass was subsequently crystallised at 800 °C for 8 h (sample B). For the preparation of another two samples, the melt was slowly cooled on a cooper plate (sample C) or cast into a graphite mould and subsequently thermally treated at 300 °C for 3 h (sample D). As shown by X-ray diffraction (XRD) and scanning electron microscopy (SEM) including energy dispersive X-ray spectroscopy (EDXS) and electron backscatter diffraction (EBSD) measurements, the rapidly cooled samples contained notable amounts of uncrystallised glassy phase next to the Aurivillius phase Bi4Ti3O12. The latter occurred in higher concentrations in all other samples and formed oriented layers. Minor concentrations of Bi2Al4O9 and Al2O3 were also detected in the microstructure.

“…The coarser crystals at their core but finer crystals at their periphery indicate a decreasing growth velocity during dendrite formation; hence, they probably grew during the primary cooling process similar to the peculiar mullite crystals observed in the bulk of a glass with the molar composition 22.5MgO•22.5Al 2 O 3 •55SiO 2 . 25 Considering that the crystallization of Ba-fresnoite leads to such a release of energy that it may heat its own growth front (e.g., by more than 70 K) when growing in a melt, 16 it is plausible that such a crystallization may locally counter the cooling process during initial glass production until the undercooling rate becomes too high. As in Figure 7, a clear difference between the crystals allowing EBSD analysis and the surrounding, also highly crystallized glass-ceramic is not discernible in the SEM micrographs.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Hindering the Kinetic Selection of Dendritic Ba-Fresnoite by Phase Separation in a Glass of the Near-Eutectic Composition Ba₂TiSi₂O₈–2.625SiO₂

Crystal Growth & Design

Švančárek²,

Parchovianský

et al. 2019

Self Cite

A glass with the near-eutectic molar composition of 2BaO·TiO2·4.625SiO2 (BT2.625S) in the Ba-fresnoite–SiO2 system is produced and crystallized at 850, 880, 910, or 1100 °C. The resulting surface crystallized layer is analyzed using scanning electron microscopy (SEM) including electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). In agreement with related glass compositions, this glass shows oriented nucleation at the surface. However, a phase previously not observed in the Ba-fresnoite–SiO2 system is detected and indicated to be brookite (TiO2) by XRD, as well as EBSD results. Crystal growth into the bulk occurs via the dendritic mechanism, but when crystallizing at 1100 °C, the dendrites are severely disturbed by droplets resulting from phase separation, which also hinders kinetic selection.