Crystal Growth And Properties Characterization Of Rare-earth-doped Relaxor-based Ferroelectric Materials

The relaxor-based ferroelectric single crystal PMNT(Pb(Mg1/3Nb2/3)O3-Pb Ti O3) shows excellent ferroelectric, piezoelectric and dielectric properties, and a higher phase transition temperature, receiving extensive concern for these outstanding performances. In recent years, the growth problem of large size and high quality PMNT single crystals has been successfully solved,as a result of which, a large number of applications arise. Lead-free piezoelectric ferroelectrics represented by NBT(Na1/2Bi1/2Ti O3) single crystal also have superior ferroelectric and piezoelectric properties, which have incomparable advantages in the aspect of environmental protection, compared to lead materials. Based on the current research progress of rare-earth-doped ferroelectrics with up-conversion emission, rare earth ions were introduced respectively into two kinds of typical ferroelectric single crystal, PMNT and NBT, the changes of electrical and optical properties of which were investigated, in this thesis.Er3+A-site and B-site doped PMNT polycrystalline material with perovskite structure were synthesized separately by two-step solid-state reaction at elevated temperature, and whether Er3+ions occupy the A-site or the B-site was controlled through the stoichiometric ratio. Er3+different site doped PMNT single crystals were grown from the polycrystalline material melts through the solution Bridgman technique by using PMNT seed crystals. The obtained crystals were characterized to have the only perovskite phase by XRD, and Er3+ ions were doped smoothly according to phase structure characteristics and the absorption or transmission spectrum. The crystals were characterized for their ferroelectric and dielectric properties. The curie temperatures of Er3+A-site and B-site doped PMNT single crystals are 111~115℃ and 125~127℃, lower than undoped PMNT. The change of ferroelectric and dielectric properties at room temperature is related to the site Er3+ions occupy: The A-site improves, and by contrast the B-site deteriorates.PLE, PL and UC spectrum show excellent fluorescence properties of the Er3+-doped crystals, and upon the excitation of 980 nm, they both exhibit strong green emissions clearly visible with the naked eye.Good quality undoped NBT single crystal was grown by vertical Bridgman method for the first time we tried, using which as the seed, fine Er3+-doped and Pr3+-doped NBT single crystals were also obtained separately. The compositions were modulated to be(Na1/2Bi1/2)0.985Er0.01TiO3and(Na1/2Bi1/2)0.985Pr0.01TiO3. The perovskite phases of the polycrystalline materials and the obtained crystals were characterized by XRD, and Er3+ and Pr3+ did not destroy the perovskite structure of NBT. Compared to the undoped NBT crystal, Curie temperatures of the rare-earthdoped NBT crystals reduce, and, dielectric constant and loss of the Er3+-doped decrease slightly but the ones of the Pr3+-doped increase. Transmission and PLE, PL spectrum of Er3+-doped and Pr3+-doped NBT single crystals prove same to other Er3+-doped and Pr3+-doped solid mediums. Er3+-doped NBT single crystal emits bright green light because of high UC luminescence intensity upon the excitation of 980 nm.