Due to the high structural flexibility and controllable thermal expansion, cubic double ReO 3 -type negative thermal expansion (NTE) fluorides provide a solution for solving the prominent phenomenon of thermal expansion mismatch between materials. However, the expensive raw materials and complex synthesis steps limit its practical application. In this work, we have designed a more advantageous method for the synthesis of NTE material CaZrF 6 , and it is expected to be generalized to the synthesis of other double ReO 3 -fluorides. Intriguingly, a new orthorhombic phase CaZrF 6 has been synthesized via this method in a lower temperature. Unlike the strong isotropic NTE of the cubic phase CaZrF 6 , the orthorhombic phase shows the strong anisotropic positive thermal expansion (PTE). The combined analysis of temperature-dependent X-ray diffraction (XRD), Raman spectra, and first-principles calculations shows that the low frequency phonon vibration mode with negative Grüneisen parameter in cubic CaZrF 6 are strongly correlated with the transverse thermal vibration of F atoms and dominates the NTE of the material.
Keqiang Zhang,Kai Wei,Jiaxin Chen,Bo Liang,Daining Fang,Rujie He
Ceramics and their structures with tunable thermal expansion are deemed necessary to develop. In this study, multi-ceramic structures with tunable thermal expansion, including negative thermal expansion (NTE), zero thermal expansion (ZTE), and positive thermal expansion (PTE), were developed for the first time. Firstly, multi-ceramic triangle structures with tunable thermal expansion were designed based on ZrO 2 and Al 2 O 3 ceramics. Then, multi-ceramic triangle structures were fabricated by using the stereolithography additive manufacturing technology. Functionally gradient ceramic (FGC) layers were applied for releasing the thermal mismatch stress among the structure. Finally, the thermal expansion behavior of the multi-ceramic triangle structures were characterized and analyzed by using a homemade thermal expansion testing system. The proposed design, fabrication and characterization methods of multi-ceramic structures with tunable thermal expansion are believed to promote the engineering application.
危险品化学品经营许可证（带存储）