MBi2Ge2O8 molten glasses: A new host environment for the growth of garnets,spinels, and related phases

The molar volumes of MO/Bi₂O₃/2 GeO₂ glasses ($\text{M= Zn, Cd, Ca, Sr, Pb, \& Ba}$) vary directly with cation volume and inversely with cation field strength. Small needles of ZnBi₂Ge₂O₈ (up to 0.75 mm) & SrBi₂Ge₂O₈ (up to 0.20 mm) can form during slow cooling of the parent melts. Al₂O₃ (or Ga₂O₃) additions expand these glasses by introducing AlO₄ Tetrahedra. Precipitation of spinel-like arrays from such molten polyhedral jumbles requires more Al₂O₃ (or Ga₂O₃) with larger cations for solubility reasons. This is confirmed by the nuclei concentrations.