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Study on lattice vibrational properties and Raman spectra of Bi_2Te_3 based on density-functional perturbation theory 下载免费PDF全文
We present a variational density-functional perturbation theory(DFPT) to investigate the lattice dynamics and vibrational properties of single crystal bismuth telluride material. The phonon dispersion curves and phonon density of states(DOS) of the material were obtained. The phonon dispersions are divided into two fields by a phonon gap. In the lower field,atomic vibrations of both Bi and Te contribute to the DOS. In the higher field, most contributions come from Te atoms. The calculated Born effective charges and dielectric constants reveal a great anisotropy in the crystal. The largest Born effective charge generates a significant dynamic charge transferring along the c axis. By DFPT calculation, the greatest LO–TO splitting takes place in the infrared phonon modes and reaches 1.7 THz in the Brillouin zone center. The Raman spectra and peaks corresponding to respective atomic vibration modes were found to be in good agreement with the experimental data. 相似文献
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采用基于溶质扩散控制模型CA方法对Ti-45at.% Al合金定向凝固过程中显微组织演化过程进行了数值模拟.模拟结果表明,在温度梯度较高时,初生晶核间距无论大小,均可通过分枝或竞争生长而使一次胞晶/枝晶间距得到调整.在抽拉速度一定情况下,随着温度梯度增加,胞晶/枝晶间距减小,在温度梯度一定情况下,随着抽拉速度增大,观察到胞晶/枝晶混合结构,混合结构区随温度梯增大而增大,模拟结果与实验观察相符合.
关键词:
Ti-45at.% Al合金
定向凝固
组织演化
数值模拟 相似文献
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利用溶质扩散控制模型对TiAl合金柱状晶/等轴晶转变过程进行了数值模拟,结果表明,等轴晶在柱状晶前沿形核及生长过程中,当两个扩散场相遇时,观察到成分冲击波,它可能是导致柱状晶停止生长的一个主要原因.利用该模型,对小铸件柱状晶/等轴晶转变过程进行了预测,在模拟过程中发现柱状晶界面前沿液相温度梯度,成分过冷度可联合对柱状晶/等轴晶转变产生影响,模拟与实验观察符合较好.
关键词:
TiAl合金
成分冲击波
柱状晶/等轴晶转变 相似文献
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确定材料在高温高应变率下动态性能的Hopkinson杆系统 总被引:15,自引:4,他引:11
描述了一种利用Hopkinson杆装置确定在高温(温度可高达1 173 K)、高应变率下材料动态性能的试验方法。在试样加温过程中,试样不与入射杆及透射杆接触。当试样加热到预定温度时,气压驱动同步组装系统,推动透射杆及试样,使得应力波到达入射杆与试样接触面时,入射杆、试样及透射杆紧密接触。利用以上系统,完成了连铸单晶铜及上引法连铸多晶铜从室温到1 085 K范围内的应力应变曲线。测试结果表明,不论是上引法连铸多晶铜还是连铸单晶铜,流动应力随温度的升高而下降,在温度低于585 K时,材料的应变硬化率明显大于在温度高于585 K时的应变硬化率。 相似文献
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Probing the thermoelectric transport properties of n-type Bi2Te3 close to the limit of constitutional undercooling 下载免费PDF全文
Bulk n-type Bi2Te3 single crystals with optimized chemical composition were successfully prepared by a high temperature-gradient directional solidification method. We investigate the influence of alloy microstructure, chemical composition, and growth orientation on the thermoelectric transport properties. The results show that the composition of single-crystal Bi2Te3 alloy, along the c axis direction, could be slightly tuned by changing the growth rate of the crystal. At a rate of 18 mm/h, the formed Bi2Te3 crystal exhibits good thermoelectric properties. At 300 K, a maximum Seebeck coefficient of -245 μV/K and an electrical conductivity of 5.6 × 10 4 S/m are acquired. The optimal power factor is ob- tained as 3.3 × 10 -3 W/K2m, with a figure of merit of 0.74. It can be attributed to the increased tellurium allocation in the Bi2Te3 alloys, as verified well by the density functional theory caLculations. 相似文献
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