Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang, Sichuan 621900, China.
Earth and Planetary Science, University of California, Berkeley, California 94720, USA.
Phys Rev Lett. 2018 May 25;120(21):215703. doi: 10.1103/PhysRevLett.120.215703.
We report continuous measurements of the sound velocity along the principal Hugoniot curve of α quartz between 0.25 and 1.45 TPa, as determined from lateral release waves intersecting the shock front as a function of time in decaying-shock experiments. The measured sound velocities are lower than predicted by prior models, based on the properties of stishovite at densities below ∼7 g/cm^{3}, but agree with density functional theory molecular dynamics calculations and an empirical wide-regime equation of state presented here. The Grüneisen parameter calculated from the sound velocity decreases from γ∼1.3 at 0.25 TPa to 0.66 at 1.45 TPa. In combination with evidence for increased (configurational) specific heat and decreased bulk modulus, the values of γ suggest a high thermal expansion coefficient at ∼0.25-0.65 TPa, where SiO_{2} is thought to be a bonded liquid. From our measurements, dissociation of the molecular bonds persists to ∼0.65-1.0 TPa, consistent with estimates by other methods. At higher densities, the sound velocity is close to predictions from previous models, and the Grüneisen parameter approaches the ideal gas value.
我们报告了在 0.25 到 1.45 TPa 的压力范围内，通过衰减激波实验中侧向释放波与冲击波前缘相交的时间函数，对 α 石英主 Hugoniot 曲线进行的连续测量，得到了声速。测量的声速低于先前基于密度低于约 7 g/cm^{3}时的 stishovite 性质的模型预测，但与密度泛函理论分子动力学计算和此处提出的经验宽区状态方程一致。从声速计算出的 Grüneisen 参数从 0.25 TPa 时的 γ∼1.3 下降到 1.45 TPa 时的 0.66。结合证据表明比热增加（构型）和体弹性模量降低，γ 值表明在 ∼0.25-0.65 TPa 范围内具有较高的热膨胀系数，在此范围内认为 SiO_{2} 是一种结合液体。根据我们的测量结果，分子键的解离持续到 ∼0.65-1.0 TPa，与其他方法的估计一致。在更高的密度下，声速接近先前模型的预测，Grüneisen 参数接近理想气体值。
