权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Search for silica polymorphs denser than stishovite

寻找比石英石更致密的二氧化硅多晶型物

基本信息

批准号：
02640629
负责人：
MATSUI Yoshito
金额：
$ 0.96万
依托单位：
Okayama University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1991
项目状态：
已结题

项目摘要

A hypothetical polymorph of silica with the hydrazinium dichloride structure and denser than stishovite by ca. 6 %, was discovered by the present author and co-investigators in 1988. The transition pressure of stishovite to the predicted new polymorph is, however, too high to be significant within the Earth's mantle.A systematic survey in search for other polymorphs has been carried out by following way : By means of the molecular dynamics calculation assuming empirical and non-empirial two-body potentials for the Si-O system, behaviours under compression up to 200 GPa have been investigated on virtually all known AX_2 and A_2X compounds at 300 K. The results show that the following four types are fundamental structures for silica under pressures : 1) the retile type(known as stishovite), 2)the alpha-PbO_2 type, 3)the hydrazinium dichloride type and 4)the orthorhombic ZrO_2 type. Among them, the already studied type(the hydrazinium dichloride type)showed the highest density. If follows that the rutile type and the CaCl_2-type silica(the latter being the high pressure modification of the rutile type)is only stable within deep interior of the Earth. So the project failed to discover any miracle structure(s).During the course of the study, remarkable phonon softing was observed in the rutile type silica. At -l5O GPa(the value critically depending on assumed potential parameters)the frequency of acoustic phonon mode TA fall to zero, still holding a tetragonal symmetry, and orthorhombic CaCl_2 structure becomes stable at - 160 GPa. The mechanism of this peculiar behaviour has been intersively studied by molecular dynamics, lattice dynamics and by modeling according to the Ginzburg-Landau model.

1988年，作者和合作研究人员发现了一种假设的多晶型二氧化硅，其结构为二氯化肼，密度比辉石高约6%。然而，辉锌矿向预测的新多晶型的转变压力太高，在地幔内没有意义。为了寻找其他多晶型，我们通过以下方式进行了系统的调查：通过对Si-O系统假定经验的和非经验的两体势的分子动力学计算，研究了几乎所有已知的AX_2和A_2X化合物在300K下的压缩行为。结果表明，以下四种类型是压力下二氧化硅的基本结构：1)折返型(称为辉锌矿)，2)α-PbO_2型，3)二氯化肼类化合物和4)正交晶系氧化锆类化合物。其中，已研究的类型(二氯化肼类型)显示出最高的密度。由此可见，金红石型和CaCl2型二氧化硅(后者是金红石型的高压变质)只在地球深部稳定。因此，该项目没有发现任何神奇的结构(S)。在研究过程中，金红石型二氧化硅中观察到了显著的声子软化。声学声子模TA的频率在-15 GPa时降至零，仍保持四方对称性，正交CaCl2结构在-160 GPa时趋于稳定。用分子动力学、晶格动力学和Ginzburg-Landau模型对这种特殊行为的机理进行了相互作用的研究。