Desenvolvimento de métodos assistidos por radiação micro-ondas para a síntese direta e rápida de niobato de lítio (LiNbO3).

Abstract

Lithium niobate (LiNbO3) is an important ferroelectric material applied in sensorics, piezoelectric transducers, catalysis and optical devices. Its properties and applicability are influenced by the particle size and chemical composition and lithium content. At high synthesis or process temperatures (> 600 °C), lithium can evaporate and favor the formation of secondary phases. To reduce or minimize this problem the development of mild synthesis methods must be consider. Among these methods, the hydrothermal and combustion have been featured. Even if offering advantages, a successful hydrothermal synthesis can take up to 4 days for LiNbO3, while the combustion method can need additional heating processing steps. Both methods can be enhanced through the use of microwaves radiation, which result in time and energy savings and the direct synthesis of the desired material in particles or structures of nanometric scale with good uniformity. However, the use of microwaves applied on this methods for LiNbO3 are either not described or understudied. Thus, microwave-assisted hydrothermal and combustion methods were developed. The hydrothermal method developed allowed the direct synthesis of rhomboedric and cubic nanoparticles of LiNbO3 with average size of 41 nm and 52 nm in only 2 h and 3 h at 260 °C. Compared to the previous studied conventional hydrothermal synthesis and the Pechini methods, it offers better morphology and size homogeneity and is relatively easier to prepare. The combustion method developed offers simplicity, requiring less steps for preparation and use of simpler precursor reactants, resulting in the direct synthesis of LiNbO3 within 20- 60 s. In general, both methods allow the direct synthesis of LiNbO3 with no presence of secondary phases and within very short times compared to the respective conventional methods which they derive.