声子在β-锂霞石锂扩散、热膨胀和相变中的作用：非弹性中子散射和晶格动力学研究
Role of Phonons in Li-Diffusion, Thermal Expansion and Phase Transitions in beta-eucryptite: Inelastic Neutron Scattering and Lattice Dynamics Studies
摘要：
β锂霞石（LiAlSiO 4）具有一维超离子导电性和各向异性的热膨胀行为。我们在300 - 900 K温度范围内进行了β-锂霞石的非弹性中子散射测量，并用从头算密度泛函理论方法计算了声子谱。计算出的能量分布的合作锂离子位移表明，在高温阶段的锂离子沿六方c轴的优先运动。然而，当在晶体中引入肖特基缺陷时，Li离子扩散的能垒显著降低。此外，声子谱的各向异性应力依赖性的计算，以获得沿各个轴的热膨胀行为。计算结果表明，低能声子模的Gruneisen参数在10 meV附近具有较大的负值，并控制着沿a轴和c轴的负热膨胀行为.另一方面，各向异性弹性以及在30至70 meV范围内的高能量模式的Gruneisen参数的各向异性正值负责a-b平面中的正热膨胀和沿c轴的负膨胀。声子模偏振矢量的分析揭示了反常热膨胀行为的机理。我们扩展了研究，讨论了在布里渊区的软声子与所观察到的高压和高温相变的文献报道的关系。
英文摘要：
Beta eucryptite (LiAlSiO4) shows one-dimensional super-ionic conductivity as well as anisotropic thermal expansion behavior. We have performed inelastic neutron scattering measurements in beta eucryptite over 300 to 900 K and calculated the phonon spectrum using ab initio density functional theory method. The calculated energy profile for cooperative lithium ion displacements indicates preferential movement of Li ion along the hexagonal c-axis in the high temperature phase. However, the energy barrier for Li ion diffusion is significantly reduced when a Schottky defect is introduced in the crystal. Further, the anisotropic stress dependence of the phonon spectrum is calculated to obtain the thermal expansion behavior along various axes. The calculations show that the Gruneisen parameters of the low-energy phonon modes around 10 meV have large negative values and govern the negative thermal expansion behavior both along the a and c axes. On the other hand, anisotropic elasticity along with anisotropic positive values of the Gruneisen parameters of the high-energy modes in the range 30 to 70 meV are responsible for positive thermal expansion in the a-b plane and negative expansion along the c-axis. The analysis of the polarization vectors of the phonon modes sheds light on the mechanism of the anomalous thermal expansion behavior. We extend the study to discuss the relationship of the soft phonons in the Brillouin zone with the observed high-pressure and high-temperature phase transitions as reported in the literature.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
