Crystal growth and dielectric properties of BaTiO3 obtained in aluminoborosilicate glasses

• Synthesis of invert glasses with high 3d transition metal concentration
• Crystallization of barium titanate for various Na to Al ratios is achieved.
• Dependence of the crystal size on the ratio Na/Al is established.
• High dielectric constants are determined for the prepared glass-ceramics.

The synthesis of invert glasses in the system Na2O/TiO2/BaO/Al2O3/B2O3/SiO2/Fe2O3 is reported for different [Na2O]/[Al2O3]-ratios and glass-former concentration less than 30 mol%. During annealing in the glasses cubic and tetragonal BaTiO3 crystals are simultaneously crystallized as proved by X-ray diffraction. Scanning electron microscopy micrographs show that during isothermal heat-treatment globular crystals with sizes from 100 nm to 1 μm are formed. The dielectric properties of the glass-ceramics are studied at room temperature by impedance spectroscopy using two contact points measurement and gold electrodes. The impedance and the phase angle are measured in the frequency range from 0.1 Hz to 1 MHz. The obtained impedance spectra are simulated using an appropriate equivalent circuit in order to extract information on the bulk resistance and capacitance of the sample. Measurements of the capacitance at fixed frequencies are carried out and the dielectric constants are calculated. High dielectric constants in the order of 1000 at a frequency of f = 13 Hz are estimated, which increase with the increasing annealing times and decrease with increasing frequencies.