Very high or close to zero thermal expansion by the variation of the Sr/Ba ratio in Ba1−xSrxZn2Si2O7 – solid solutions

Abstract

The compound BaZn₂Si₂O₇ shows a highly positive coefficient of thermal expansion. At a temperature of 280 °C, it transforms to a high temperature phase, which exhibits a coefficient of thermal expansion near zero. The partial replacement of Ba²⁺ against Sr²⁺ leads to a decrease of the phase transition temperature. If more than 10% of Ba²⁺ are replaced by Sr²⁺, the high-temperature phase is completely stable at room temperature and consequently, the thermal expansion is near zero or negative. The effect of the Sr²⁺/Ba²⁺-ratio on the phase transition temperature and the thermal expansion behavior is measured using high-temperature X-ray diffraction up to 1000 °C. The Sr²⁺/Ba²⁺-ratio strongly affects the overall thermal expansion as well as the anisotropy. The latter increases with decreasing Sr-concentration. The strong differences in the thermal expansion behavior between phases with the structure of the low-temperature phase and the high-temperature phase of BaZn₂Si₂O₇ can be explained by a comparison of the ZnO₄-chains inside these two crystal structures.