Glass-ceramics containing ferroelectric bismuth germanate (Bi2GeO5)

Glasses have been formed from the BiO1.5–GeO2–BO1.5 system and a study made of their devitrification behaviour and the properties of the glass-ceramics obtained. Crystals of the ferroelectric phase, orthorhombic Bi2GeO5, are precipitated in all of the glass compositions studied and this is the dominant phase in the region of 60 mol% BiO1.5:20 mol% GeO2:20 mol% BO1.5. The microstructures of the glass-ceramics have been found to change dramatically on altering the crystallisation temperature, yielding spherulites or surface crystallisation which can be used to produce oriented growth. The dielectric behaviour and ferroelectric hysteresis loop of a selected Bi2GeO5 glass-ceramic show that this material can be ferroelectric at room temperature with Ps=14 μC/cm2.