Hydrothermal Synthesis Of LiTaO₃ Nanopowders And Dielectric Properties Of Their Sinters

LiTaO3 is an important piezoelectric and ferroelectric material. As the competition of lead-free piezoelectric ceramics in investigation and exploiture increasingly vehement, the excellent properties of LiTaO3 ceramics are far-ranging cared by scholars. The ceramic powders made by hydrothermal synthesis are symmetrical component, small grain size, high purity, no agglomerated or less agglomerated and its shape and size can be controlled. Especially, it does not need high temperature to calcine, so it avoids grain growth, defect-forming and impurity introduction. For these reasons, the powder has high sintering activity.In the thesis, LiTaO3 nanoparticles were synthesized by hydrothermal method. The influences of several factors, such as starting materials, temperature and reaction time on microstructure of 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 optimal conditions of synthesis are obtained as following: reactants are Li2CO3 and Ta2O5, reaction temperature is 240℃and reaction time is 12h. The powder under optimal conditions was characterized by thermal analysis (TG-DTA). The average particle size and morphology were studied by transmission electron microscopy (TEM). TEM and X-ray powder diffraction data show that the average size of particles was about 30nm. The Curie temperature is between 630℃and 720℃.Under the definite reaction condition, Fe-doped,Ce-doped and Cu-doped LiTaO3 nanoparticle ceramic powders were studied. The results indicated that, the lattice parameters and crystal volume turned small when doped iron or cuprum. The lattice parameters and crystal volume became large when cerium-doped.The ceramic powders synthesized by hydrothermal method were sintered as starting materials. Structure and morphology of LiTaO₃ sinters in different ion-doped and sintered at different temperature were investigated by means of SEM. And then dielectric properties of the samples were measured by wide-band LCD digital electric bridge. The result indicated that LiTaO3 sinters with high density and quality can be obtained at 1000℃. The sintering temperatures had obvious effect on both the room-temperature relative dielectric constant and dielectric loss. Dielectric property of the sinter obtained at 1000℃was better than other temperatures. The room-temperature relative dielectric constant of LiTaO3 sinters were increased due to cerium-doped as well as dielectric loss were decreased to some extent, while the room-temperature relative dielectric constant and dielectr- ic loss of LiTaO3 sinters were decreased due to iron-doped.