高压Na_2O-SiO_2系输运性质反常的分子模拟

Transport Property Anomalies under High Pressure in Molten Na_2O-SiO_2 Binary System Studied by Molecular Dynamics Simulation

在6000K,0～100GPa范围内,对一系列Na2O-SiO2二元系进行了分子动力学模拟.这些体系包括SiO2、Na2O·10SiO2、Na2O·5SiO2、Na2O·2SiO2、Na2O·SiO2、2Na2O·SiO2.模拟结果显示,在前4个体系中,氧扩散系数随压力变化反常.在Na2O·10SiO2,Na2O·5SiO2,Na2O·2SiO2中,硅的扩散系数随压力变化也出现反常.在这些体系中,20GPa处氧的扩散系数比常压下高出一个数量级.在上述各体系中,氧扩散系数随压力变化的峰值都在20GPa处,以前报导的SiO2体系中氧扩散系数随压力变化的峰值在30GPa处.还观察到,在SiO2体系中,氧扩散系数最大值大致相当于硅-氧配位数以五配位为主;而在Na2O·10SiO2体系中,氧扩散系数最大值大致相当于硅-氧配位数以六配位为主.

A series of ion dynamics simulations on Na2O-SiO2 binary system at 6000 K ranging from 0 to 100 GPa pressure have been carried out. These systems include SiO2, Na2O . 10SiO(2), Na2O . 5SiO(2), Na2O . 2SiO(2), Na2O . SiO2, 2Na(2)O . SiO2. The simulated results show that there exists anomalous pressure dependence for oxygen component diffusion coefficient in SiO2, Na2O . 10SiO(2), Na2O . 5SiO(2), Na2O . 2SiO(2) systems. Besides SiO2 system, others have not been reported earlier. In Na2O . 10SiO(2), Na2O . 5SiO(2), Na2O. 2SiO(2) systems, the silicon component diffusion coefficient also shows anomalous pressure dependence, this result has not been reported earlier. In these systems at about 20 GPa the diffusion coefficient of oxygen component is larger than that at ambient pressure by more than an order of magnitude. That the pressure-induced peak position of oxygen diffusion coefficient is at about 20 GPa is different from the results reported earlier, which is at about 30 GPa. It is observed that the diffusivity maximum in SiO2 system corresponds approximately to a prevalence of five-coordination of silicon by oxygen, but the diffusivity maximum in Na2O . 10SiO(2) system corresponds approximately to a prevalence of six-coordination of silicon by oxygen. The latter has not been reported earlier.