β─BaB_2O_4晶体生长母液结构的分子动力学模拟研究

MOLECULAR DYNAMICS STUDY ON THE STRUCTURE OF β BaB 2O 4 GROWTH SOLUTIONS

采用分子动力学模拟方法，研究了βＢａＢ２Ｏ４晶体生长母液ＢａＢ２Ｏ４Ｎａ２Ｏ二元系熔体的结构，Ｎａ２Ｏ摩尔浓度分别为１２５％，２０％，２５％，３０％．模拟给出的不同组分比下的ＢＯ径向分布函数表明，随着Ｎａ２Ｏ浓度的增加，第一峰峰值更高，峰形更尖锐．在模拟产生的一系列瞬态构型基础上，采用键序参数方法，结合环链统计，研究了母液溶体的局部结构．结果表明，助熔剂Ｎａ２Ｏ的加入，提高了熔液中ＢＯ３平面三角形基团的含量，且使游离ＢＯ３，Ｂ２Ｏ５，Ｂ３Ｏ７等结构单元增多，同时大大削弱了体系网联程度，有利于平面Ｂ３Ｏ６环的形成，也有利于晶体生长．统计分析还表明，Ｂ原子在游离ＢＯ３中的百分比与母液熔体挥发度实验值。

Abstract The structures in β BaB 2O 4(BBO) growth solutions, which are BaB 2O 4 Na 2O binary melts with different molar concentrations of Na 2O(12 5%,20%,25%,30%), have been studied by molecular dynamics simulations. The simulated B O radial distribution functions with different Na 2O concentrations show that the first peaks become high and sharp with the increasing of Na 2O concentration. Based on the instantaneous configurations given by the simulations, the local structures of the binary melts were analyzed by means of the bond order parameter method combined with the statistics of rings and chains. The results indicate that the adding of Na 2O as a flux into the melt systems will make more planar BO 3 structure units and more isolated BO 3, B 2O 5 and B 3O 7 clusters while the network in the melts will be greatly weaken, which are all beneficial to the forming boroxol groups B 3O 6 and the growing of BBO crystal. The statistics also shows that the percentages of B atoms in isolated BO 3 and the percentages of B atoms in long chains are in good agreement with the experimental values of volatility and viscosity of hte solution systems, respectively.