Thermal expansion of Ba2ZnSi2O7, BaZnSiO4 and the solid solution series BaZn2−xMgxSi2O7 (0≤x≤2) studied by high-temperature X-ray diffraction and dilatometry

The thermal expansion behavior of Ba2ZnSi2O7, BaZnSiO4 and BaZn2Si2O7 is characterized by both high-temperature X-ray diffraction (HT-XRD) and dilatometry. Ba2ZnSi2O7 and BaZnSiO4 show a thermal expansion (100–800 °C) in the range from 8.9 to 10.4 × 10−6 K−1. By contrast, BaZn2Si2O7 has a much higher thermal expansion in the low-temperature modification and shows a phase transition at 280 °C which runs parallel with a steep increase in cell volume. This phase transition is also observed in the solid solution series BaZn2−xMgxSi2O7, but it is shifted to higher temperatures and to a smaller volume change with increasing Mg2+ concentration. This solid solution series is characterized by dilatometry, X-ray diffraction and differential scanning calorimetry. An adjustment of the MgO/ZnO-ratio enables the preparation of materials with a large variety of thermal expansions.