Equations of state and structures of andalusite to 9.8 GPa and sillimanite to 8.5 GPa
Equations of state and structures of andalusite to 9.8 GPa and sillimanite to 8.5 GPa
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DOI：
10.2138/am.2006.1875
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发表时间：
2006-02
影响因子：
3.1
通讯作者：
J. B. Burt;N. Ross;R. Angel;M. Koch
中科院分区：
文献类型：
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作者：
J. B. Burt;N. Ross;R. Angel;M. Koch
用高压单晶X射线衍射法测定了红柱石和硅线石的状态方程和结构。用三阶Birch-Murnaghan状态方程拟合红柱石在1bar和9.8GPa之间测得的14个P-V数据点，得到KT_0 = 144.2（7）GPa和K' = 6.8（2）。对硅线石进行类似的分析，涉及拟合1巴和8.5 GPa之间的13个P-V数据点，结果为KT 0 = 164（1）GPa和K' = 5.0（3）。两种结构的轴向压缩均为非线性和高度各向异性（~60%），其中c轴是两种结构中的最小可压缩轴。用三阶Birch-Murnaghan状态方程的参数化形式确定的轴向模量为：硅线石的K_a = 163（1）GPa，K_b = 113.1（7）GPa，K_c = 297（1）GPa，其中K_a = 2.1（3），K_b = 5.08（19），K_c = 11.1（4），K_a = 99.6（7）GPa，红柱石Kb = 152.2（9）GPa，Kc = 236（3）GPa，K 'a = 5.83（19），K' b = 7.6（3），K 'c = 5.5（9）。在这两种结构中的主要压缩机制涉及缩短键长内的AlO 6八面体的体积减少7.4%和5.1%的硅线石和红柱石，分别在研究的压力范围内。在红柱石也有显着的压缩的AlO 5多面体，并在较小程度上，SiO 4四面体，显示减少5.0%和3.1%的体积，分别。在硅线石中，AlO 4或SiO 4四面体都没有明显的压缩，它们表现为刚性的不可压缩单元。
Abstract The equations of state and structures of andalusite and sillimanite have been determined using high-pressure single-crystal X-ray diffraction. A third-order Birch-Murnaghan equation-of-state fit to 14 P-V data points measured between 1 bar and 9.8 GPa for andalusite yields values of KT0 = 144.2(7) GPa and K’ = 6.8(2). A similar analysis for sillimanite involving a fit to 13 P-V data points between 1 bar and 8.5 GPa results in KT0 = 164(1) GPa and K’ = 5.0(3). The axial compression of both structures is nonlinear and highly anisotropic (~60%) with the c-axis being the least compressible axis in both structures. The axial moduli determined with a parameterized form of the third-order Birch-Murnaghan equation of state are: Ka₀ = 163(1) GPa, Kb₀ = 113.1(7) GPa, and Kc₀ = 297(1) GPa with K’a₀ = 2.1(3), K’b₀ = 5.08(19), and K’c₀ = 11.1(4) for sillimanite, and Ka₀ = 99.6(7) GPa, Kb₀ = 152.2(9) GPa, and Kc₀ = 236(3) GPa with K’a₀ = 5.83(19), K’b₀ = 7.6(3), and K’c₀ = 5.5(9) for andalusite. The major compression mechanism in both structures involves shortening of bond lengths within the AlO6 octahedra with volume reductions of 7.4% and 5.1% in sillimanite and andalusite, respectively, over the pressure ranges studied. In andalusite there is also significant compression of the AlO5 polyhedra and, to a lesser degree, the SiO4 tetrahedra that display reductions of 5.0% and 3.1% in volume, respectively. In sillimanite there is no significant compression of either the AlO4 or SiO4 tetrahedra which behave as rigid, incompressible units.