用第一性原理计算研究沿[110]和[111]方向有序的Ba Ti O3/Sr Ti O3(BTO/STO)1∶1超晶格的晶格动力学、介电和压电性能.对两种有序BTO/STO超晶格从最高对称性的结构出发计算布里渊区中心声子,通过冻结不稳定声子得到畸变结构,进一步冻结...用第一性原理计算研究沿[110]和[111]方向有序的Ba Ti O3/Sr Ti O3(BTO/STO)1∶1超晶格的晶格动力学、介电和压电性能.对两种有序BTO/STO超晶格从最高对称性的结构出发计算布里渊区中心声子,通过冻结不稳定声子得到畸变结构,进一步冻结不稳定声子得到基态结构.两种有序BTO/STO超晶格的基态结构分别是Pm和R3m结构.把声子介电张量和内应变压电张量分解成单个离子和单个声子的贡献.根据离子对介电和压电张量各分量的贡献可知Ti和O离子对介电和压电有比较大的贡献.声子对介电和压电张量的贡献的分析果表明频率较低的声子有主要的贡献.特别是沿[110]方向有序BTO/STO超晶格中ε11主要来自于频率为49 cm-1的软模A'声子的贡献.展开更多
We have performed first principles calculations of Fe-doped BaTiO3 and SrTiO3. Dopant formation energy, structure distortion, band structure and density of states have been computed. The dopant formation energy is fou...We have performed first principles calculations of Fe-doped BaTiO3 and SrTiO3. Dopant formation energy, structure distortion, band structure and density of states have been computed. The dopant formation energy is found to be 6.8eV and 6.5eV for Fe-doped BaTiO3 and SrTiO3 respectively. The distances between Fe impurity and its nearest O atoms and between Fe atom and Ba or Sr atoms are smaller than those of the corresponding undoped bulk systems. The Fe defect energy band is obtained, which mainly originates from Fe 3d electrons. The band gap is still an indirect one after Fe doping for both BaTiO3 and SrWiO3, but the gap changes from Γ-R point to Γ-X point.展开更多
A series of c-axis oriented BaTiO3/SrTiO3 superlattices with the atomic-scale precision were epitaxially grown on single-crystal SrTiO3(100) substrates using laser molecular-beam epitaxy (LMBE). A periodic modulation ...A series of c-axis oriented BaTiO3/SrTiO3 superlattices with the atomic-scale precision were epitaxially grown on single-crystal SrTiO3(100) substrates using laser molecular-beam epitaxy (LMBE). A periodic modulation of the intensity of reflection high-energy electron diffraction (RHEED) in BaTiO3 and SrTiO3 layers was observed and attributed to the lattice-misfit-induced periodic variation of the terrace density in film surface. The relationship between the second-order nonlinear optical sus-ceptibilities and the superlattice structure was systematically studied. The experimental and theoretical fitting results indicate that the second-order nonlinear optical susceptibilities of BaTiO3/SrTiO3 superlattices were greatly enhanced with the maximum value being more than one order of magnitude larger than that of bulk BaTiO3 crystal. The mechanism of the enhancement of the second-order optical non-linearity was discussed by taking into account the stress-induced lattice distortion and polarization enhancement.展开更多
BSTO dielectric ceramic was prepared from SrTi03 and BaTi03 powders synthesized by hydrothermal method, as well as from Bao.sSro.4TiO3 powder synthesized by conventional solid-state reaction. The former can be sintere...BSTO dielectric ceramic was prepared from SrTi03 and BaTi03 powders synthesized by hydrothermal method, as well as from Bao.sSro.4TiO3 powder synthesized by conventional solid-state reaction. The former can be sintered at a relatively low temperature of 1120 ℃. Characterization by SEM showed that the grain shapes of both ceramics are cubical, though the grain size of the former is much smaller. Dielectric constants measured at 20℃ were shown to vary with frequency in the range from I kHz to 2 MHz and dc bias field, and further that the dielectric loss of the former to be less than 2 × 10^- 3 in the frequency range of 20 kHz to 1 MHz, much smaller than that of the latter sample. For the former, temperature dependence of dielectric constant is much flatter and there exists an extended phase transition diffusion covering a wide temperature range of Curie temperature To. The smaller grain size of the former depresses the dc bias electrical field dependence of dielectric constant. The tunability is 7% under a bias field of 0.6 kV/mm dc.展开更多
Barium titanate （BaTiO3） and strontium titanate （SrTiO3） nanoparticles were synthesized separately through hydrothermal reaction of crystalline TiO2 particles and corresponding alkaline earth hydroxides, Ba（OH）2...Barium titanate （BaTiO3） and strontium titanate （SrTiO3） nanoparticles were synthesized separately through hydrothermal reaction of crystalline TiO2 particles and corresponding alkaline earth hydroxides, Ba（OH）2 and St（OH）2 respectively, in 50 mol·dm^-3 KOH solution at 150℃. Each structural evolution of BaTiO3 and SrTiO3 during the hydrothermal treatment was investigated by X-ray diffraction （XRD）, field emission scanning electron microscopy （FE-SEM）, field emission transmission electron microscopy （FE-TEM） and thermogravimetry- differential analysis （TG-DTA）. In the BaTiO3 system, round particles with cubic perovskite-type structure were obtained within 1 h. However, these particles were gradually dissolved and then were re-precipitated in the form of cube-shape BaTiO3 particles with a smaller lattice constant ac than that of the former phase. After the BaTiO3 particles formed firstly have disappeared completely, or the two phases coexistence stage with different lattice constant ac passed, lattice constant ac of BaTiO3 phase re-precipitated continuously decreased with annealing time. In contrast, once SrTiO3 particles are formed, the lattice constant ac decreased continuously throughout the reaction. The result indicates that SrTiO3 particles were annealed without dissolution and precipitation process under the present condition.展开更多
文摘用第一性原理计算研究沿[110]和[111]方向有序的Ba Ti O3/Sr Ti O3(BTO/STO)1∶1超晶格的晶格动力学、介电和压电性能.对两种有序BTO/STO超晶格从最高对称性的结构出发计算布里渊区中心声子,通过冻结不稳定声子得到畸变结构,进一步冻结不稳定声子得到基态结构.两种有序BTO/STO超晶格的基态结构分别是Pm和R3m结构.把声子介电张量和内应变压电张量分解成单个离子和单个声子的贡献.根据离子对介电和压电张量各分量的贡献可知Ti和O离子对介电和压电有比较大的贡献.声子对介电和压电张量的贡献的分析果表明频率较低的声子有主要的贡献.特别是沿[110]方向有序BTO/STO超晶格中ε11主要来自于频率为49 cm-1的软模A'声子的贡献.
文摘We have performed first principles calculations of Fe-doped BaTiO3 and SrTiO3. Dopant formation energy, structure distortion, band structure and density of states have been computed. The dopant formation energy is found to be 6.8eV and 6.5eV for Fe-doped BaTiO3 and SrTiO3 respectively. The distances between Fe impurity and its nearest O atoms and between Fe atom and Ba or Sr atoms are smaller than those of the corresponding undoped bulk systems. The Fe defect energy band is obtained, which mainly originates from Fe 3d electrons. The band gap is still an indirect one after Fe doping for both BaTiO3 and SrWiO3, but the gap changes from Γ-R point to Γ-X point.
文摘A series of c-axis oriented BaTiO3/SrTiO3 superlattices with the atomic-scale precision were epitaxially grown on single-crystal SrTiO3(100) substrates using laser molecular-beam epitaxy (LMBE). A periodic modulation of the intensity of reflection high-energy electron diffraction (RHEED) in BaTiO3 and SrTiO3 layers was observed and attributed to the lattice-misfit-induced periodic variation of the terrace density in film surface. The relationship between the second-order nonlinear optical sus-ceptibilities and the superlattice structure was systematically studied. The experimental and theoretical fitting results indicate that the second-order nonlinear optical susceptibilities of BaTiO3/SrTiO3 superlattices were greatly enhanced with the maximum value being more than one order of magnitude larger than that of bulk BaTiO3 crystal. The mechanism of the enhancement of the second-order optical non-linearity was discussed by taking into account the stress-induced lattice distortion and polarization enhancement.
基金support from the Shan-dong Sinocera Functional Material Co., Ltd
文摘BSTO dielectric ceramic was prepared from SrTi03 and BaTi03 powders synthesized by hydrothermal method, as well as from Bao.sSro.4TiO3 powder synthesized by conventional solid-state reaction. The former can be sintered at a relatively low temperature of 1120 ℃. Characterization by SEM showed that the grain shapes of both ceramics are cubical, though the grain size of the former is much smaller. Dielectric constants measured at 20℃ were shown to vary with frequency in the range from I kHz to 2 MHz and dc bias field, and further that the dielectric loss of the former to be less than 2 × 10^- 3 in the frequency range of 20 kHz to 1 MHz, much smaller than that of the latter sample. For the former, temperature dependence of dielectric constant is much flatter and there exists an extended phase transition diffusion covering a wide temperature range of Curie temperature To. The smaller grain size of the former depresses the dc bias electrical field dependence of dielectric constant. The tunability is 7% under a bias field of 0.6 kV/mm dc.
文摘Barium titanate （BaTiO3） and strontium titanate （SrTiO3） nanoparticles were synthesized separately through hydrothermal reaction of crystalline TiO2 particles and corresponding alkaline earth hydroxides, Ba（OH）2 and St（OH）2 respectively, in 50 mol·dm^-3 KOH solution at 150℃. Each structural evolution of BaTiO3 and SrTiO3 during the hydrothermal treatment was investigated by X-ray diffraction （XRD）, field emission scanning electron microscopy （FE-SEM）, field emission transmission electron microscopy （FE-TEM） and thermogravimetry- differential analysis （TG-DTA）. In the BaTiO3 system, round particles with cubic perovskite-type structure were obtained within 1 h. However, these particles were gradually dissolved and then were re-precipitated in the form of cube-shape BaTiO3 particles with a smaller lattice constant ac than that of the former phase. After the BaTiO3 particles formed firstly have disappeared completely, or the two phases coexistence stage with different lattice constant ac passed, lattice constant ac of BaTiO3 phase re-precipitated continuously decreased with annealing time. In contrast, once SrTiO3 particles are formed, the lattice constant ac decreased continuously throughout the reaction. The result indicates that SrTiO3 particles were annealed without dissolution and precipitation process under the present condition.
