Crystallization and dielectric properties of SrO–BaO–Nb₂O₅–GeO₂ tungsten–bronze glass–ceramics

The crystallization and dielectric properties of SrO–BaO–Nb₂O₅–GeO₂ glass–ceramics were investigated. One- and two-stage heat-treatment methods were used to convert the parent glass to glass–ceramics. Strontium barium niobate (SBN) with a tetragonal tungsten-bronze structure formed as the major crystalline phase. When the crystallizing temperature/time was increased, the secondary crystalline BaGe₂O₅ phase coexisted with SBN. BaGe₂O₅ formed as a surface layer grown from the surface into the interior of the sample. The dendritic morphology of SBN crystals was examined. The glass–ceramics crystallized by two-stage heat treatment have higher dielectric constants than those crystallized by one-stage heat treatment. The highest dielectric constant that was obtained in the present glass–ceramics was 320. The glass–ceramics showed relaxor-type dielectric behavior.