Study of Sr-to-Ba Ratio Effect on Ferroelectricity of Strontium Barium Niobate by Multi-scale Simulation methods

• Main Authors: Yi-AnSun, 孫逸安
• Other Authors: Wen-Dung Hsu
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/23389382308098615604

碩士 === 國立成功大學 === 材料科學及工程學系 === 104 === Strontium barium niobate-based series material SrxBa1-xNb2O6 (SBN) has excellent ferroelectric properties, as well as pyroelectric and piezoelectric properties. SBN can transform from ferroelectric material to relaxor by tuning Sr/(Sr+Ba) ratio. When Sr/(Sr+Ba) ratio is 0.25 (x 〉 0.25), it shows normal ferroelectric behavior. As the Sr/(Sr+Ba) ratio increases from 0.6, it begins to show relaxor behavior until Sr/(Sr+Ba) ratio reaches 0.75. For Sr/(Sr+Ba) ratio above 0.8, it lost spontaneous polarization and shows no ferroelectric properties. In this study first-principles calculation was used to reveal the Sr/(Sr+Ba) ratio dependent ferroelectric properties of SBN. The structure of SBN with x = 0.4, 0.6, 0.8 were determined by special quasirandom structure (SQS) method first and then optimized by the Vienna Ab initio simulation package (VASP). The results show that Sr/(Sr+Ba) ratio will influences the deviation of Niobium ions in octahedral sites and the distance between cation and anion. Those displacements of ions are then proved to have large influence on the magnitude of spontaneous polarization; thus it is considered to be the mechanism that responsible for the Sr/(Sr+Ba) ratio dependent ferroelectric properties of SBN. Besides we also developed born model for SBN to simulate polar nanoregion by molecular dynamic simulation. It is found that pattern of polar nanoregions is closely related to Sr/(Sr+Ba) ratio in SBN.