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.

XRD-patterns of Ba2ZnSi2O7 were recorded at different temperatures (left). For each XRD-pattern a Rietveld-refinement was performed, the image in the middle shows the XRD-pattern measured at room temperature (circles), the Rietveld calculation (red line) and the difference between them (blue line). The lattice parameters derived hereof were plottet against the temperature and fitted to a polynomial (right picture). From those polynomials the lattice expansion was calculated.Figure optionsDownload as PowerPoint slideHighlights
► We examined the thermal expansion of Ba2ZnSi2O7, BaZnSiO4 and BaZn2−xMgxSi2O7.
► Thermal expansions were determined by dilatometry and high-temperature X-ray diffraction.
► High-temperature X-ray diffraction enabled to determine anisotropic thermal expansion.
► BaZn2Si2O7 exhibits the highest thermal expansion due to a phase transition.
► Substitution of small amounts of Zn2+ for Mg2+ leads to a decrease in thermal expansion.