Electrical and mechanical properties of alkali barium titanium alumino borosilicate glass-ceramics containing strontium or magnesium

The AC electrical data, measured in the frequency range 0.1 Hz-5 MHz, were used to study the electrical response of lithium barium titanium alumino borosilicate glass-ceramics containing strontium or magnesium. Complex plane plot from these electrical data for various glass ceramic samples reveal contributions from simultaneously operating polarization mechanisms to overall dielectric behaviour. The SrO/BaO or MgO/Al2O3 replacements resulted in the increase of the conductivity and dielectric constant of the corresponding glass-ceramic materials. The relationships between the crystalline phases formed and dielectric values of studied glass-ceramics are complicated. The complex impedance of the crystalline materials generally decreases with the addition of SrO instead of BaO and with increase of MgO at the expense of Al2O3. The obtained data were correlated to the internal microstructure, crystalline phases formed, glassy matrix and glass to crystal interface region. beta-Spodumene together with varieties of Ba-containing phases [e. g. orthorhombic celsian-BaAl2Si2O8, fresnoite-Ba-2(TiO)Si2O7], barium silicate Ba2Si3O8, lithium borate-Li6B4O9, lithium metasilicate-Li2SiO3 strontium titanate-SrTiO3, and magnesium borate-MgB4O7 phases were mostly developed in the crystallized glasses. The microhardness characteristics of the crystalline glasses have been investigated by Knoop microhardness. The SrO/BaO or MgO/Al2O3 replacements resulted into decreasing the microhardness values. The obtained data of the glass-ceramic specimens were explained in relation to the crystalline phases, microstructure formed and the glassy matrix.