DIELECTRIC PROPERTIES OF STRONTIUM TITANATE GLASS-CERAMICS (DIELECTRIC LOSS, CONSTANT, LOW TEMPERATURE PROPERTIES, CRYSTALLIZATION)

The crystallization and dielectric properties of strontium titanate aluminosilicate glass-ceramics, containing perovskite SrTiO(,3) as the primary crystalline phase, have been investigated.;The majority of this research was concentrated on glass-ceramics consisting of 65 wt% of SrTiO(,3) and 35 wt% of silica and alumina with a silica/alumina weight ratio of 2/1 (SAR-2). In these glass-ceramics, the primary crystalline phase was perovskite SrTiO(,3); other crystalline phases included SrAl(,2)Si(,2)O(,8) (hexacelsian and anorthite) and TiO(,2) (anatase and rutile). The relative amounts of SrTiO(,3) and secondary phases, and the microstructure, were dependent on the crystallization conditions.;The dielectric properties of SAR-2 glass-ceramics were extremely sensitive to the amount of SrTiO(,3) in the glass-ceramic, and thus to the crystallization conditions. The dielectric constant increased as the crystallization temperature or time was increased, and peaks developed in the dielectric constant at low temperatures. These dielectric constant peaks were not due to dielectric mixing, and it was proposed that the peaks resulted from ferroic domains effects in the SrTiO(,3) phase of the glass-ceramic.;Several dielectric loss mechanisms were identified in these glass-ceramics. A temperature-independent (athermal) increase of dielectric loss with frequency (10 kHz to 1 MHz) was observed in all glass and glass-ceramic samples, apparently the result of the low frequency tail of a vibrational loss mechanism. High temperature, low frequency losses were observed in some samples, attributed to Maxwell-Wagner-Sillars effects, caused by the incorporation of Ti('3+) into the crystalline SrTiO(,3) phase, and also to the presence of crystalline titania. Two sets of relaxation-type loss peaks were observed at temperatures near 50 and 100K in certain glass-ceramics; these loss peaks were related to the same mechanism responsible for the low temperature dielectric constant peaks.