Papers by Keyword: Barium Strontium Titanate

Abstract: Barium strontium titanate, BST (BaxSr1-xTiO3), nanoparticles were prepared by a sol-gel hydrothermal technique. BST powders of different composition (x=0.1, x=0.3, x= 0.5, x=0.7, x=0.9) prepared by sol-gel technique previously were treated by hydrothermal synthesis method later. XRD results indicated that the as-prepared perovskite BST nanoparticles have the accurate proportioning composition. These results showed that the combination of sol-gel and hydrothermal technique would become a potential and promising process for fabricating BST and other nanopowders.

Abstract: The influence of La2O3-doping on the dielec- tric properties of Ba0.6Sr0.4TiO3-6wt%MgO was studied. With the increase of La2O3-doping content, the space between adjacent parallel crystal planes of BST-MgO composite first became larger, then smaller. Proper quantity of La2O3 could ensure moderate dielectric constant and reduce the dielectric loss of BST-MgO composite at high frequency, but excess quantity of La2O3 would lower dielectric constant. When the La2O3-doping content was 0.2wt%, the dielectric constant and loss of BST-MgO composite were equal to 93.2 and 0.005 (1MHz), respectively. And the dielectric constant tunability could be obtained to 12.1% (21kV/cm).

Abstract: Epitaxially graded barium strontium titanate (BaxSr1-x)TiO3 (x = 0.75, 0.8, 0.9, 1.0, abbreviated as BST75, BST80, BST90 and BTO respectively) thin films were fabricated by pulsed laser deposition method on the (La0.7Sr0.3)MnO3 (LSMO)/LaAlO3 (LAO) single crystal substrate. Scanning probe microscopy with a contact mode was used to characterize the temperature dependence of polarization from room temperature to 140°C. Results indicated that the piezo-response signal of the BST graded films had an obvious change with temperature, and that the graded structures had a flatter temperaturedependence of permittivity. Furthermore, the contrasts of the SPM images were lower for the ferroelectric – paraelectric (F-P) phase transition temperatures of BST 75, BST 80, and BST90, but higher for the F-P transition temperature of BTO.

Abstract: Bilayer Ba0.6Sr0.4TiO3 - Ba0.4Sr0.6TiO3 and Ba0.4Sr0.6TiO3 - Ba0.6Sr0.4TiO3 thin films were deposited on the LaNiO3-buffered Pt/Ti/SiO2/Si substrates using pulse laser deposition method. A (100)preferred orientation was obtained. The structure was characterized using x-ray diffraction (XRD) and Raman spectroscopy. The leakage current, and dielectric permittivity versus temperature were characterized. Results indicated that the (100) preferred bilayer structure had less leakage current and smaller loss tangent, which was in favor of enhancing the quality of thin film used as microwave dielectrics.

Abstract: (Ba,Sr)TiO3 films with thickness between 1 ~ 20 µm are fabricated by electrophoretic deposition using (Ba,Sr)TiO3 nanopowder synthesized by different methods including sol-gel, coprecipitation and conventional solid phase synthesis. Experiments show that conventional solid phase synthesis need higher crystallization temperature (>1000°C) and result in larger size of particle while in sol-gel and coprecipitation process (Ba,Sr)TiO3 crystallizes at lower temperature and results in smaller size of particle . Powders synthesized from various routes have different surface property. Deposition parameter must be adjusted accordingly to obtain dense and smooth (Ba,Sr)TiO3 film.

Abstract: Epitaxially grown (Ba,Sr)TiO3 thin films were prepared on platinum-coated silicon substrate by sol-gel method using a (Ba,Sr)TiO3 sol derived from Ba(CH3COO)2, Sr(CH3COO)2 and Ti(O-i-C3H7)4. The morphology of the films was found to depend on the annealing condition. A columnar structure was obtained for (Ba,Sr)TiO3 thin film by annealing at 800 °C and a columnar grain was found to be single crystal by transmission electron microscope (TEM). The columnar grown film exhibits a preferred (111) orientation that follows the (111) orientation of Pt substrate. Measurement of the C-V in MFM was configured in order to demonstrate good dielectric properties. Obtained films showed high voltage tunability.

Abstract: Diffusion behavior at the interface of (001)-epitaxially grown (Ba,Sr)TiO3(BST)/electrode/buffer layer/Si thin films was examined by use of secondary ion-microprobe mass spectrometer (SIMS) and transmission electron microscope (TEM) attached with energy dispersive X-ray fluorescence spectrometer (EDX). As the (001)-epitaxially grown film, following three kinds of structure was grown; (1)BST/(La,Sr)CoO3(LSCO)/CeO2/yttria-stabilized zirconia(YSZ)/Si, (2)BST/PLD-deposited Pt/SrTiO3(ST)/LSCO/CeO2/YSZ/Si and (3)BST/sputter-deposited Pt/ST/LSCO/CeO2/YSZ/Si. For sample (1), uphill diffusion of Sr and Ti was observed at the interface of YSZ and SiO2. Diffusion of Co into CeO2 layer was also detected. These tendencies of diffusion were also observed for samples (2) and (3). In addition to these tendencies, apparent uphill diffusion of Co at the Pt layer was observed for sample (2). However, this diffusion was not observed for sample (3). It was also observed that oxygen diffusion was prevented for sputter-deposited Pt. On the other hand, oxygen diffusion was observed for PLD-deposited Pt.