Low-temperature sintering and microwave dielectric properties of zinc metatitanate-rutile mixtures using boron

Mixtures of zinc metatitanate and rutile (ZnTiO₃+xTiO₂, where x = 0-0.5) have been prepared via the conventional mixed-oxide method. Centrifugal planetary milling with zirconia beads 1 mm in diameter produced very fine powders (mean particle size of 0.2 μm), which allowed the synthesis of ZnTiO₃ and sintering at temperatures <945 °C, which is the decomposition temperature of ZnTiO₃. Sintering of the mixtures was enhanced further by the addition of B₂O₃. Densities of >94% of the theoretical density have been attained for the specimens that were sintered at 875 °C for 4 h with B₂O₃ additions of <1 wt%. Microwave dielectric properties of the aforementioned compositions were as follows: dielectric constant of 29-31, normalized quality factor of 56000-69000 GHz, and a temperature coefficient of resonance frequency between -10 and +10 ppm/°C. Sintering was enhanced by the formation of a ZnO-B₂O₃ liquid phase, which affected the microwave properties, because of variation in the phase composition.