Synthesis And Doping Modification Of Barium Titanate Nanocrystals Derived By Static And Dynamic Hydrothermal Processes

Barium titanate (BTO) nanopowders are widely used in multilayer ceramic capacitors (MLCC) due to the high dielectric constants and low dielectric losses. Though there have been a lot of reports about the synthesis of BTO nanopowders, how to obtain the material with uniform particle sizes and excellent dispersion is still challenges. Hydrothermal synthesis method has become one of the primary means to prepare barium titanate nanocrystals owing to the low synthetic temperatures, the high purity, uniform particle size and good dispersion of the as-obtained products. In this paper, the static and dynamic hydrothermal methods were developed to synthesize highly dispersed Barium Titanate nanocrystals with uniform particle-sizes, using Ti(OC4Hg)4, Ba(NO3)2and NaOH as the main starting materials. The phase composition, morphology and microstructure of the as-obtained samples were characterized by XRD, SEM, TEM, TG and FI-TR. The effects of the Ba/Ti ratios, NaOH concentrations and hydrothermal temperatures on the phase composition and morphology were investigated. The related growth mechanisms of the dynamic and static hydrothermal synthesis of BTO nanocrystals were also discussed.(1) BTO nanocrystals have been synthesized by static hydrothermal process at the temperature of200℃for10h using TiO2sol which was obtained by the hydrolysis of Ti(OC4H9)4as the titanium source, Ba(NO3)2as the barium source, the ratio of Ba/Ti was1.5. In thi system, the concentration of TiO2sol was0.2mol/L and the concentration of NaOH was2.0mol/L. From the analysis of XRD and SEM we can be seen that that the obtained BTO nanocrystals are highly dispersed uniform solid balls (76±13nm) with smooth surface. During the study on the factors of Ba/Ti ratios (0.7-2.0), the NaOH concentrations (0.6-3.0mol/L), the hydrothermal temperatures (100-200℃), and times (10min-100h), it can be found that the tetragonal increases and the surface of crystal becomes more and more smooth with the increasing of Ba/Ti ratios, NaOH concentrations and the hydrothermal temperatures and times. The highly dispersed solid BTO nanocrystals can be gotten at the hydrothermal temperatures of180-200℃when the Ba/Ti ratios was1.2-1.5, the NaOH concentrations was1.0-3.0mol/L. During the static hydrothermal process, the precursor of barium and titanium sources fast nucleation with several nanometers of BTO nanocrystals, followed by directed gathered into uniform particles, and then generated a polyhedral structure of large particles due to_Oswald ripening mechanism.(2) Gappy hollow BTO nanocrystals had been synthesized by hydrothermal process at the temperature of180℃for20h by using TiO2sol which was obtained by the dynamic hydrolysis using Ti(OC4H9)4as the titanium source, Ba(NO3)2as the barium source and the ratio of Ba/Ti was1.2. In this system, the concentration of TiO2sol was0.2mol/L,and the concentration of NaOH was1.0mol/L. The obtained BTO nanocrystals are highly dispersed uniform gappy hollow spheres with the size of93±20nm. The effects of the Ba/Ti ratios (1.0-2.0), NaOH concentrations (1.0-3.0mol/L) and hydrothermal temperatures (100-200℃) and times (30min-50h) on the phase composition and morphology were investigated. The results show that the formation of notched hollow BTO nanocrystals has a strong relation with the Ba/Ti ratios, NaOH concentrations and hydrothermal temperatures and times. The optimal conditions of obtaining gappy hollow BTO nanocrystals are the Ba/Ti ratios higher than1.2and the NaOH concentrations lower than1.5mol/L and the hydrothermal temperatures around180℃. During the dynamic hydrothermal process, nanoparticles directly aggregated to particles in the early stages of crystal growth, and then generated a gappy hollow structure particles due to the reversed crystal growth mechanism.(3) Zr-doped BTO nanocrystals had been synthesized by a static hydrothermal process at the temperature of200℃for10h by using TiO2sols as the titanium source, Ba(NO3)2as barium source, and Zr(NO3)2as zirconium source. In the above systems, the ratio of Ba/Ti was1.5, the concentration of TiO2sol was0.2mol/L, the concentration of NaOH was2.0mol/L, and the molar amount of Zr-doped BTO nanocrystals was0.1-2%. The dielectric constant was tested by a LCR instrument. The results show that the dielectric constants increased firstly and then decreased with the increases in doping amount of Zr, and the sample with a doping amount of1%of Zr has the highest dielectric constant (5432), higher than that of undoped BTO nanocrystals by26%.