Synthesis and Neutron Diffraction of Al2TiO5: With and Without Doping

Sammanfattning

Aluminium titanate, Al2TiO5, is an interesting material due to its unique refractory properties. A negative to low thermal expansion coefficient makes the material ideal for high-temperature applications. However, Al2TiO5 decomposes into Al2O3 (corundum) and TiO2 (rutile) between 800 - 1300 °C, which limits its applicability. The decomposition can be prevented by introduction of doping elements, such as Fe2O3. The aim of this master's thesis is to explore synthesis methods of Al2TiO5 to produce samples suitable for neutron diffraction. The following results aim to improve the understanding of how Fe-doping affect the stability of Al2TiO5. Multiple synthesis methods were evaluated using X-ray diffraction (XRD) and simultaneous thermal analysis (STA). These included several solid state methods and a sol-gel approach. Conventional solid state synthesis at 1400 °C with subsequent air-cooling was proven to be one of the most successful methods, yielding a phase purity of 91 wt.%. This method was therefore used to produce undoped, Fe-doped and Zr-doped Al2TiO5, which was studied with neutron diffraction and total scattering at the ISIS Neutron and Muon Source. Preliminary results of the Fe-doped samples show a preference of the M1-site for Ti4+, and a preference of the M2-site for Al3+ and Fe3+. The lowest amount of oxygen vacancies were found on the O2-sites, which play a critical role for the structural stability of Al2TiO5, since these sites connect the metallic chains in the structure. Interestingly, vacancy filling could also be observed on the O2-site as the Fe concentration increased, which suggests a possible stabilizing mechanism for Fe-doped Al2TiO5. Total scattering data were also presented for three of the samples. The results from this master's thesis highlight a link between oxygen vacancies and Fe-doping, which hopefully can aid the future development of Al2TiO5 coatings.