Barium Titanate And Barium Strontium Titanate Nanoparticles Preparation, Crystal Structure And Microwave Absorption Performance Of The Research

Known as "the pillar of electronic ceramics", ferroelectric barium titanate (BaTiO3) is widely used in the electronic ceramics industry as its unique properties, such as high dielectric constant, low dielectric loss, excellent ferroelectric and piezoelectric properties, and good insulating properties. Barium strontium titanate (BaxSr (1-x) TiO3, BST) is also an important electronic ceramic material which is used in the manufacture of tunable microwave devices, high-density capacitors, phase-shifting device, phased array antennas and other devices. The size of electronic devices has been sharply shrinking, so the application of nanoscale BST powders becomes very extensive. The ferroelectric property of BST powder changes with the phase transition. Therefore, the phase transition research of nanometer-sized BST powder becomes very significant.In recent years, the rapid development of the microwave absorbing materials in military and mobile communications industry result in a new study trend:the research of dielectric materials. BaTiO3and BaxSr(1-x)TiO3could be good microwave absorbing candidates as there are dielectric loss exist in these ferroelectric. They can reduce and absorb microwave through electronic polarization, ion polarization and interfacial polarization. Our research is mainly focusing on the synthesis, characterization, and microwave absorption analysis of BaTiO3and BaxSr(1-x) TiO3. This paper includes two parts:1. Uniform BaTiO3nano-torus with either concave or epicenter holes are synthesized by a hydrothermal method. Experiment indicates that the BaTiO3nano-torus with an average diameter ranging from50to100nm is of tetragonal phases at room temperature. The morphology of the BaTiO3nano-torus depends on the shape of the original titanium dioxide precursor and reaction time. The microwave absorption properties of both the BaTiO3nano-torus and the BaTiO3solid nanoparticles are examined between2-18GHz microwave frequency bands. The maximum reflection loss of the BaTiO3nano-torus reaches-28.38dB at11.36GHz, compare to that of-12.87dB at16.32GHz of the BaTiO3solid nanoparticles. The nearly120%enhancement of the reflection loss in the range of8-12GHz is probably attributed to the hollow volume inside the BaTiO3nano-torus which might contribute more dissipation and scattering effects of the microwave. Growth mechanisms of the BaTiO3nano-torus are also investigated by changing both the reaction time from0.5h to48h and the reactants concentration ratio between Ba(OH)2·8H2O and titanium dioxide. Both an "in-situ transformation" mechanism and a "dissolution-precipitation" growth mode are proposed.2. Barium strontium titanate (BaxSr (1-x) TiO3BST x=1,0.91,0.65,0.5,0) nanoparticles with a size range of30-50nm are synthesized by hydrothermal method. The Raman spectroscopy indicates that the Curie temperature Tc of BST nanocrystals decline with the increasing of Sr content in BST nanocrystals. The Tc of Ba0.91Sr0.01TiO3is around room temperature while the Tc of Ba0.65Sr0.35TiO3and Ba0.5Sr0.5TiO3are below room temperature. This decrease of Tc with Sr content increase in BST nanoparticles are faster than it is in the bulk or thin film materials. At the same time, we found that the Raman spectra of BST nanoparticles appear [E (TO+LO), B1] mode at300cm-1when the measure temperature increased to a certain value which are higher than Tc. This phenomenon indicates that a reverse paraelectric to ferroelectric phase transition happened in BST nanocrystals. From now on, this unusual phase transition hasn’t been reported. It strongly suggests that when the size of BST particle shrinks to nanoscale, the symmetry is easy to be destroyed in high temperature. The microwave absorption property study of BST nanoparticles shows that BST is also a good microwave absorption candidate. With the increase of Sr content, the microwave absorption properties of BST nanoparticles enhanced. SrTiO3exhibits the largest reflection loss at12.72GHz with a value of-8.89dB. It is probably to enhance the microwave absorption property of BST nanoparticles by changing the doped content of Sr.