Limits to the Validity of Thermal-Pressure Equations of State
Limits to the Validity of Thermal-Pressure Equations of State
复制标题
热压状态方程有效性的限制
作者：
R. Angel;F. Miozzi;M. Alvaro
热-压状态方程（EoS），如Mie-Grüneisen-Debye（MGD）模型，依赖于几个假设，包括准谐波近似（QHA）和简化的声子态密度。我们展示了如何违反QHA表现出各向异性的热压材料。我们还表明，在低于参考体积的等容线的压力，静压可能会变得足够负，使压缩部分的EoS无效。该限值对EoS参数K '0、q和Grüneisen参数γ0的综合影响敏感。大的q值，对应于声子模式频率随着体积的增加而迅速降低，也可以导致体积模量在高压和高温下变为零，这对于行星地热来说不是特别极端。因此，MGD EoS具有极其有限的P和T制度，在该制度下，它既有效又具有物理意义的属性。在该范围之外，在表示固体的物理性质的热压中应包括额外的术语。或者，可替代地，可以使用“等温”EoS，其中弹性性质的温度变化被明确地建模而不参考物理模型。
Thermal-pressure Equations of State (EoS) such as the Mie-Grüneisen-Debye (MGD) model depend on several assumptions, including the quasi-harmonic approximation (QHA) and a simplified phonon density of states. We show how the QHA is violated by materials exhibiting anisotropic thermal pressure. We also show that at pressures lower than those of the isochor of the reference volume, the static pressure may become sufficiently negative to make the compressional part of the EoS invalid. This limit is sensitive to the combined effects of the EoS parameters K’0, q and the Grüneisen parameter γ0. Large values of q, which correspond to a rapid decrease in phonon mode frequencies with increasing volume, can also lead to the bulk modulus becoming zero at high pressures and temperatures that are not particularly extreme for planetary geotherms. The MGD EoS therefore has an extremely limited P and T regime over which it is both valid and has physically-meaningful properties. Outside of this range, additional terms should be included in the thermal pressure that represents the physical properties of the solid. Or, alternatively, ‘isothermal’ EoS in which the temperature variation of the elastic properties is explicitly modeled without reference to a physical model can be used.
莫来石型Bi{sub 2}Al{sub 4}O{sub 9}的热膨胀：X射线衍射、振动光谱和密度泛函理论研究
影响因子：
3.3
作者：
Murshed;Mendive;Sehovic;Friedrich;Fischer;Gesing;Th. M.
通讯作者：
Th. M.