Ferroelectric glass-ceramics from the PbO–GeO2–Nb2O5 system

Glass-ceramics with compositions Pb5Ge3O11–xPbNb2O6 (PG–xPN) where x equals 0.0, 0.5, 1, 2 and 3, and other selected compositions from the PbO–GeO2–Nb2O5 system, have been prepared using the conventional melt-quench method. Most of the quenched melts devitrified on cooling and gave fragile samples. The x=0.5 (PGN2) sample formed a robust solid which contained the ferroelectric phase Pb5Ge3O11 and the pyrochlore phase Pb2Nb2O7. Glass formation was improved by replacing some Nb2O5 by GeO2. Scanning electron micrographs of cross-sections of the x=0.5 sample showed surface crystallisation of the PG phase with a-axis orientation. The PN phase was distributed randomly in the sample. Heating the sample at 667 °C for 48 h enhanced the surface orientation of this PG phase. After poling the heat treated sample, using an electric field of up to 25 kV/cm, a ferroelectric hysteresis loop could be obtained at room temperature with Ps=1 μC/cm2. The Curie point of this PGN2 sample was found to be ∼166 °C.