Papers by Keyword: SrTiO3

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Ferroelectricity of SrTiO3 Thin Films Prepared by Dynamic-Aurora Pulsed Laser Deposition
Authors: Kiyotaka Yamashita, Yoshihiro Sakamaki, Naonori Sakamoto, Kazuo Shinozaki, Hisao Suzuki, Naoki Wakiya
Abstract: The effect of in-situ magnetic field during deposition (dynamic aurora PLD) was examined for SrTiO3 thin film deposited on (La0.5Sr0.5)CoO3/CeO2 buffered YSZ(001) substrates. It was found that both in-plane and out-of-plane lattice parameters were changed by the in-situ magnetic field. Reciprocal space map measurement revealed that the in-plane and out-of-plane lattice parameters are 0.3817 and 0.3953 nm without magnetic field, meanwhile those are 0.3906 and 0.3974 nm with magnetic fields of 2 kG. This indicates that biaxial strain induced by the magnetic field. The effect of magnetic fields on the ferroelectric properties was examined.
11
Synthesis of SrTiO3 Nanoparticles by a pH-Varying Sol-Gel Process
Authors: N. Yongvanich, P. Visuttipitukkul
Abstract: SrTiO3 is one of the most technologically important dielectric ceramics. In this paper, SrTiO3 nanoparticles were synthesized by a simple sol-gel route using NaOH to adjust the pH of the system. Three different strontium-containing starting precursors (Sr(NO3, SrCl2.6H2O and Sr(CH3COO)2.0.5H2O) were employed. Thermogravimetric analysis (TGA) showed complete decomposition of organics at approximately 800°C; this temperature was chosen as a calcination temperature. At 800°C, 6 hours, only the nitrate route with pH = 10 gives single-phase SrTiO3. Other conditions yield various impurities, most likely due to the incompletion of the reaction although they still contain very broad XRD peaks corresponding to SrTiO3, signifying the probable phase formation capability at these conditions. The obtained SrTiO3 powders are in the nanoscale range of 10 to 40 nm with isotropic morphology.
471
The Effect of Reoxidation on Thermal Shock Resistance of SrTiO3-Based Varistors
Authors: Atsushi Hitomi, Naoki Chida, Minoru Ogasawara, Dai Matsuoka
Abstract: The fabrication processes of SrTiO3-based varistors were investigated to obtain highly thermal-shock-resistant devices. It has been found that the reoxidation conditions are strongly related to the thermal cracking ratio (%) of the varistors. A large compressive stress was generated on the varistor surface by reoxidation, consequent upon the lattice parameter difference between its surface portion and its internal portion. This residual stress on the surface is thought to be the key factor of the achieved thermal-shock-resistance.
529
Synthesis of Na0.5Bi0.5TiO3 Submicron Particles in Molten Salt
Authors: Paisan Setasuwon, S. Kijamnajsuk
Abstract: Powder size is a major factor determining the characteristics of processing variables and end-products of ceramic materials. Na0.5Bi0.5TiO3 is one of the potential candidates for non-lead piezoelectric materials, synthesis of Na0.5Bi0.5TiO3 particles in molten salt was studied. Two salt systems, NaCl-KCl and Na2SO4-3K2SO4 were investigated. Only at 850°C and above, BNT was completely formed without any secondary phases in both eutectic chloride and sulfate salt. By substituting chloride with sulfate, the particle size of BNT could be greatly reduced to a few hundreds nanometer at 850°C. Submicron particles of SrTiO3 could also be synthesized in eutectic sulfate salt at 850°C, It is evident that molten salt synthesis could be employed to produce submicron particles of Na0.5Bi0.5TiO3 and SrTiO3. Molten salt synthesis is low-cost and capable to produce fine powders of various complex-oxides.
161
Study of Inelastic Light Scattering in LaxSr(1-1.5x)TiO3
Authors: A. Almeida, Tatiana M. Correia, M.R. Chaves, Paula M. Vilarinho, Andréi L. Kholkin
Abstract: In an attempt to gain a better understanding of the lattice dynamics in lanthanum doped SrTiO3 (STO) ceramics, with general formulae LaxSr(1-1.5x)TiO3, we have carried out a detailed Raman study of the x=0.0133 ceramic in the temperatures ranging from 10K to room temperature. Our results show that lanthanum substitution gives rise to new features in the Raman spectra. The Rayleigh band and the extra Raman-forbidden infrared active modes observed provide evidence for the existence of disorder in the system, apparently associated with grain structure, and lattice defects. Moreover, the absence of a TO1 polar soft mode supports the non-existence of a ferroelectric phase at low temperatures. The shift of the para-antiferrodistorsive transition temperature towards higher temperatures clearly evidences that the replacement of Strontium by Lanthanum occurs at the lattice A-site.
148
(1-x)(K0.44Na0.52Li0.04)(Nb0.84Ta0.10Sb0.06)O3-xSrTiO3 Lead Free Piezoelectric Ceramics
Authors: Ming He Cao, Wan Qiang Wang, Zhi Yong Yu, Hua Hao, Han Xing Liu
Abstract: (1-x)(K0.44Na0.52Li0.04)(Nb0.84Ta0.10Sb0.06)O3-xSrTiO3 (KNNT-ST) lead free piezoelectric ceramics have been synthesized by a solid state reaction method. The effect of SrTiO3 content on the piezoelectric properties, sintering behavior and microstructure of (1-x) KNNT-x ST ceramics was investigated. The experimental results showed that the addition of SrTiO3 can restrain the volatilization of Na ions and K ions and improve relative density of the samples. A morphotropic phase boundary between orthorhombic and tetragonal phases is found in the composition range of 0.03
1896
Electromagnetic Property of MnZn Ferrite/SrTiO3/PTFE Composites
Authors: Hai Bo Yang, Ying Lin, Fen Wang
Abstract: MnZn ferrite powder was modified by SrTiO3 sol and then filled into PTFE matrix to form MnZn ferrite/SrTiO3/PTFE composite. The effect of modification and heat-treatment on the electromagnetic property of the composite was investigated. The results revealed that the as-prepared composite possessed high permeability, high permittivity and low loss. The modification and heat-treatment could improve the electromagnetic property of the composites. The frequency dependence of the dielectric property of the composite is accorded with Debye relaxation theory.
629
Disruption of Dislocation Cores at Grain Boundary in Nb-Doped SrTiO3 Bicrystals
Authors: S.Y. Choi, J.P. Buban, Naoya Shibata, Takahisa Yamamoto, Yuichi Ikuhara
Abstract: Bicrystals of Nb-doped SrTiO3, having tilt angles of 4o~18 o with respect to [001], were prepared by joining two single crystals at 1873 K and then investigated to identify the effect of tilt angle on the grain boundary structure. The boundaries consisted of a regular array of dislocations but the positioning of cores along the boundary was found to be changed from a line to a zigzag as a tilt angle was increased up to 10o. The 14° - tilted boundary exhibited two kinds of boundary region exist at the same grain boundary; (1) the discrete cores region as observed in 4° ~ 10° - tilted boundaries and (2) the randomly oriented region as found in the 18° boundary. Thus it was observed that the structure of low-angle tilt boundary changed from the discrete dislocation structure to the randomly oriented structure as a tilt angle increases. These structural changes at the grain boundaries are considered to be related to a minimization of strain due to the high density of dislocations.
869
Grain Boundary Atomic Structures in SrTiO3 and BaTiO3
Authors: Takahisa Yamamoto, Teruyasu Mizoguchi, S.Y. Choi, Yukio Sato, Naoya Shibata, Yuichi Ikuhara
Abstract: SrTiO3 bicrystals with various types of grain boundaries were prepared by joining two single crystals at high temperature. By using the bicrystals, we examined their current-voltage characteristics across single grain boundaries from a viewpoint of point defect segregation in the vicinity of the grain boundaries. Current-voltage property in SrTiO3 bicrystals was confirmed to show a cooling rate dependency from annealing temperature, indicating that cation vacancies accumulate due to grain boundary oxidation. The theoretical results obtained by ab-initio calculation clearly showed that the formation energy of Sr vacancies is the lowest comparing with Ti and O vacancies in oxidized atomosphere. The formation of a double Schottky barrier (DSB) in n-type SrTiO3 is considered to be closely related to the accumulation of the charged Sr vacancies. Meanwhile, by using three types of low angle boundaries, the excess charges related to one grain boundary dislocation par unit length was estimated. In this study, we summarized our results obtained in our group.
851
Effect of Source Supply Methods on Low-Temperature Preparation of Lead Zirconate Titanate Thin Films Using SrTiO3 Seed Layers by Metallorganic Chemical Vapor Deposition
Authors: Ji Won Moon, Shogo Tazawa, Naoki Wakiya, Takanori Kiguchi, Youhei Ishida, Nobuyasu Mizutani, Kazuo Shinozaki
Abstract: Pb(Zr, Ti)O3 thin films were successfully prepared on (111)Pt/IrO2/SiO2/(100)Si substrates using SrTiO3 seeds at 290 oC by RF inductive heating type and 350 oC by resistive heating type metalorganic chemical vapor deposition method (MOCVD), respectively. The SrTiO3 was chosen as seed layers and prepared by pulsed laser deposition method. The crystal structures and orientations of SrTiO3 seeds were changed by deposition temperature. In the case of preparation with RF inductive heating MOCVD, the remanent polarization (2Pr) and coercive field (2Ec) were 42 μC/cm2 and 256 kV/cm, respectively.
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