Zero thermal expansion in ZrMg1-xZnxMo3O12

Abstract Ceramics with near-zero thermal expansion are rare, especially when this feature includes near room temperatures. Phases from A2M3O12 and ABM3O12 were identified as candidates for near-zero thermal expansion due to their structural features. It is supported by in situ X-ray Powder Diffraction and Raman Spectroscopy data that the ZrMg1-xZnxMo3O12 system (0≤x ≤ 0.3) presents zero thermal expansion over a wide temperature range, including room temperature. Partial substitution of Mg2+ in octahedral sites by larger Zn2+ is followed by unexpected unit-cell contraction, possibly due to covalency contraction effect of Zn–O bonds. ZrMgMo3O12 presents αl = - 4.28 × 10−7 °C-1, while partial substitution reduced αl to the values as low as - 2.02 × 10−7 °C-1 and - 2.54 × 10−7 °C-1 for x = 0.1 and x = 0.2, respectively. This feature might be ascribed to covalency contraction of Zn–O bonds and increase of rigidity of octahedra. High-temperature Raman spectroscopy revealed blue-shift of some frequency modes, responsible for near-zero thermal expansion in this system. This system is a good candidate for thermal shock resistance application, since presents near-zero thermal expansion and does not show phase transition close to room temperature and is not hygroscopic.