Síntese e estabilidade térmica do óxido, Al2(MoO4)3, obtido pelo método de coprecipitação

Abstract

The family of inorganic compounds A2(MO4)3 exhibits a diverse range of applications in the fields of microelectronics, optics, photoelectrochemistry, and photocatalysis. Due to the significant interest in these materials, studies have been directed towards understanding the properties that give rise to their applicability. Much of the performance of these materials is due to their structural configurations, controlled through synthesis. In this work, Al2(MoO4)3 was successfully synthesized via aqueous co-precipitation followed by thermal treatment. An investigation of the structural evolution and thermal stability was carried out using thermogravimetry, differential scanning calorimetry, and X-ray diffraction techniques. Based on the thermal analyses, the thermal treatment temperatures were defined to study the crystalline evolution of the amorphous precipitate. At 570 °C/1h, Al2(MoO4)3 with a monoclinic crystal system and P121/a1 space group was obtained. For a more detailed structural study, Rietveld refinement was performed. Through refinement, the crystal system was precisely defined, and lattice parameters and unit cell volume were determined, highlighting a slight contraction in the lattice with increasing thermal treatment temperature. The unit cell of Al2(MoO4)3 was modeled based on atomic coordinates, distances, and atomic angles, also obtained through Rietveld calculation. Different levels of distortions were observed in the AlO6 octahedral and/or MoO4 tetrahedral polyhedra. The average crystal size was observed to increase from 63 to 73 nm with increasing temperature from 700 to 770 °C, as determined using the Scherrer method. Finally, the thermal stability of Al2(MoO4)3 was studied, revealing the existence of incongruent sublimation at 1000 °C, giving rise to different intermediate phases of Al2O3. No molybdenum phase was observed, leading to the hypothesis that molybdenum oxide sublimation had occurred. This reaction is not predicted by the Al2O3-MoO3 phase diagram and has not yet been reported in the literature.