Hydrothermal Synthesis Of LiNbO₃ Nanopowders And Dielectric Properties Of Their Sinters

As the competition of lead-free piezoelectric ceramics in investigation and exploiture increasingly vehement, the excellent properties of LiNbO₃ ceramics are far-ranging cared by scholars in many countries. It is difficult to gain densification, integrality and good capability LiNbO₃ ceramics by traditional solid-state reaction and agglomeration method. In recent years, for making ceramics powder with symmetrical component and small grain size, wet chemistry methods are developing quickly. Especially, the ceramics powder made by hydrothermal synthesis does not need high temperature calcinations, so it avoids grain growth, defect-forming and impurity introduction. For these reasons, the powder has high sintering activity.In the thesis, LiNbO₃ nanoparticles were hydrothermally synthesized at 240℃for 12h using Li2CO₃ and Nb2O5 as starting materials by carefully controlling conditions in the first place. The influences of several factors such as: starting materials, temperature and reaction time on resultant products were investigated in the hydrothermal process by means of X-ray diffraction (XRD), infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The powder under optimal conditions was characterized by thermal analysis (TG-DTA), transmission electron microscopy (TEM) and X-ray fluorescence (XRF).The crystals reported in this condition have perfect crystal morphologies. TEM and X-ray powder diffraction data show consistent with the crystallite size of 50nm. Stoichiometry is obtained by hydrothermal method while the Curie temperature is 1180℃.In the next place, Fe-doped and Ce-doped LiNbO₃ nanoparticles ceramics powders were synthesized by hydrothermal method in the determined conditions respectively. The effect of ion-doped on lattice structure, chemical elements, ultraviolet spectrophotometry and crystal appearance characteristics of the powders was analyzed. The results indicated that: when ion-doped quantity was not more than 0.1%, there was no obviously transformation in the lattice structure; the ratio of Nb and Li which transformed to mol was less than 1:1 in the Fe-doped (0.1%) LiNbO₃; there were no notably change about ultraviolet...