Processing and Properties of Eu3+-Doped Barium Bismuth Titanate (BaBi4Ti4O15) Glass-Ceramic Nanocomposites

Precursor glasses for the ferroelectric barium bismuth titanate (BaBi4Ti4O15) (BBiT) have been prepared by the melt-quench technique in the SiO2-K2O-BaO-Bi2O3-TiO2 (SKBBT) glass system with and without Eu2O3 doping. BBiT glass-ceramic (GC) nanocomposites have been derived from these glasses by controlled heat treatment. The structural properties of the GCs have been investigated using X-ray diffraction (XRD), electron microscopy (FE-SEM, TEM), and FT-IR reflectance spectroscopy. FE-SEM images show the formation of randomly oriented hexagonal rod-shaped crystals of 200-400nm and TEM images show 10-20nm crystallites. FT-IR spectra exhibit the characteristic bands of BBiT at 480, 585, and 680cm(-1). The activation energy of crystallization (E-c) varies from 295 to 307kJ/mol. The dielectric constants (epsilon(r)) of glass and GC nanocomposites increase with an increase in frequency up to 3.0MHz and then decrease up to 5.0MHz. Heat-treated GCs show higher epsilon(r) values, in the range 25-55, compared to the precursor glasses (20-37). Dielectric losses (tan ) for all the samples increase from 0.005 to 1.0 with an increase in frequency from 100Hz to 5.0MHz. Excitation spectra were recorded by monitoring emission at 613nm corresponding to the D-5(0) F-7(2) transition. An intense 466nm excitation band corresponding to the F-7(0) D-5(2) transition was observed. Emission spectra were then recorded by exciting the glass samples at 466nm. Longer heat-treatment times led to a 15-fold increase in the intensity of the red emission at 612nm, attributed to the segregation of Eu3+ ions into the low phonon energy BBiT crystallites. The hardness (3.8-5.1GPa) and fracture toughness (1.8-3.5MPam(0.5)) values obtained in the GCs are high and suitable for structural applications.