The rheology of olivine and spinel magnesium germanate (Mg2GeO4):: TEM study of the defect microstructures
The rheology of olivine and spinel magnesium germanate (Mg2GeO4):: TEM study of the defect microstructures
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DOI：
10.1007/s002690050142
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发表时间：
1998-08-01
影响因子：
1.4
通讯作者：
Doukhan, JC
中科院分区：
文献类型：
--
作者：
Dupas-Bruzek, C;Tingle, TN;Doukhan, JC
用分析透射电子显微镜研究了合成的α-Mg_2GeO_4（具有橄榄石结构）和γ-Mg_2GeO_4（具有尖晶石结构）多晶在高温高压下在其各自的稳定区中的变形。平均晶粒尺寸为20-30 μ m的样品通过位错滑移和/或攀移变形。滑翔对爬升的优势取决于应力和晶粒取向。两种多晶型物的缺陷微观结构与在它们各自的硅酸盐类似物α-和γ-（Mg，Fe）（2）SiO 4中观察到的非常相似，并且在尖晶石相的情况下，与在铝酸镁尖晶石中观察到的非常相似。这些观察结果表明，Mg 2GeO 4是一个很好的流变学模拟地球上地幔。尖晶石试样变形的温度和应变速率相同的条件下，作为橄榄石试样约三倍强于橄榄石。在1400 K或更高温度下变形的两相样品中，沿沿着一些晶界检测到由Mg、Ge和O组成的非晶薄膜。直径小于或等于10 μ m的晶粒被非晶相膜（厚度>10 nm）包围，显示出低位错密度，并且变形似乎是通过晶界滑动发生的。
Synthetic polycrystals of alpha-Mg2GeO4 (with the olivine structure) and gamma-Mg2GeO4 (with the spinel structure) deformed at high temperature and pressure in their respective stability fields were investigated by analytical transmission electron microscopy. Specimens with a mean grain size of 20-30 mu m deform by dislocation glide and/or climb. The predominance of glide versus climb depends on stress and grain orientation. The defect microstructures of both polymorphs are very similar to those observed in their respective silicate analogues, alpha- and gamma- (Mg,Fe)(2)SiO4, and, in the case of the spinel phase, very similar to those observed in magnesium aluminate spinels. These observations suggest that Mg2GeO4 is a good rheological analogue for the Earth's upper mantle. A spinel specimen deformed under the same conditions of temperature and strain rate as an olivine specimen was approximately three times stronger than olivine. Ln specimens of both phases deformed at or above 1400 K, a thin amorphous film composed of Mg, Ge, and O was detected along some grain boundaries. Grains less than or equal to 10 mu m diameter surrounded by a film of amorphous phase (>10 nm thick) exhibited low dislocation densities, and deformation appeared to have occurred by grain boundary sliding.