Sol–gel powder synthesis and preparation of ceramics with high- and low-temperature polymorphs of BaxSr1-xZn2Si2O7 (x = 1 and 0.5): A novel approach to obtain zero thermal expansion

Samples with the stoichiometry BaZn2Si2O7 as well as Ba0.5Sr0.5Zn2Si2O7 were prepared using a sol–gel procedure. Hot pressing led to dense and crack free specimens. The BaZn2Si2O7 samples showed a steep increase in volume in the temperature range from 130 to 400 °C attributed to the transition of the low temperature to the high temperature phase. The coefficient of thermal expansion of the Ba0.5Sr0.5Zn2Si2O7 sample was close to zero at temperatures up to 130 °C and then approaches a value of 4 × 10−6 K−1 up to a temperature of 900 °C. Ba0.5Sr0.5Zn2Si2O7 powders prepared by conventional solid state reactions could not be fully densified by the supplied hot pressing procedure. Their thermal expansion was strongly negative and showed a strong hysteresis. This is the first report on dense sintered ceramics based on the SrO/BaO/ZnO/SiO2 system with thermal expansion close to zero.

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