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首页> 外文期刊>Journal of synchrotron radiation >Local structure and mean-square relative displacement in SiO_2 and GeO_2 polymorphs
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Local structure and mean-square relative displacement in SiO_2 and GeO_2 polymorphs

机译：SiO_2和GeO_2多晶型物的局部结构和均方相对位移

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Extended X-ray absorption fine structure (EXAFS) spectra near the Si and Ge K-edge for SiO_2 and GeO_2 polymorphs were measured in transmission mode with synchrotron radiation at the Photon Factory, Tsukuba. The local structures and mean-square relative displacements were determined in #alpha#-tridymite, #alpha#-quartz and stishovite. In stishovite, Si is octahedrally coordinated and the four coplanar Si-O bonds [1.755(8)A] are shorter than the other two axial bonds [1.813(15)A]. The high-temperature phase tridymite [1.597(3)A] has a smaller local bond distance than #alpha#-quartz [1.618(5)A]. The temperature variation of the local structural parameters for quartz-type GeO_2 (q-GeO_2) and rutile-type GeO_2(r-GeO_2) have been determined in the temperature range 7-1000K. The harmonic effective interatomic potential V(#mu#)=#alpha##mu#~2/2 was evaluated from the contribution to the thermal vibration, where #mu# is the deviation of the bond distance from the location of the potential minimum. The potential coefficient #alpha# for the Ge-O bond of the tetrahedron in q-GeO_2 is 24.6 eV A~(-2). The potential coefficients #alpha# for the four coplanar Ge-O bonds and the two axial bonds of the octahedron in r-GeO_2 are 12.9 and 14.9eV A~(-2), respectively. The potential coefficients #alpha# for the second-nearest Ge-Ge distance in q-GeO_2 is 9.57eV A~(-2). The potential coefficients #alpha# for the second-and third-nearest Ge-Ge distances in r-GeO_2 are 11.6 and 7.18eV A~(-2), respectively. The effective interatomic potential is largely influenced by the local structure, particularly by the coordination numbers. The phonon dispersion relations for q-GeO_2 and r-GeO_2 were estimated along [100] by calculating the dynamical matrix using the potential coefficients #alpha# for the Ge-O and Ge-Ge motions. The quartz-type structure has a more complex structure with a wide gap between 103 and 141meV and a highest energy of 149meV, whereas the rutile-type structure has a continuous distribution and a highest energy of 126meV.
机译：在筑波光子工厂，用同步辐射在透射模式下测量了SiO_2和GeO_2多晶型物在Si和Ge K边缘附近的扩展X射线吸收精细结构（EXAFS）光谱。在＃alpha＃-tridymite，＃alpha＃-石英和stishovite中确定了局部结构和均方相对位移。在辉石中，Si是八面体配位的，四个共面的Si-O键[1.755（8）A]比其他两个轴向键[1.813（15）A]短。高温相鳞石英[1.597（3）A]的局部键合距离比＃alpha＃-石英[1.618（5）A]小。确定了石英型GeO_2（q-GeO_2）和金红石型GeO_2（r-GeO_2）的局部结构参数在7-1000K的温度范围内的温度变化。根据对热振动的贡献来评估谐波有效原子间电势V（#mu＃）=＃alpha ## mu＃〜2/2，其中＃mu＃是键距与电位最小值位置的偏差。 q-GeO_2中四面体的Ge-O键的电势系数＃alpha＃为24.6 eV A〜（-2）。 r-GeO_2中四个共面Ge-O键和八面体的两个轴向键的电势系数＃alpha＃分别为12.9和14.9eV A〜（-2）。 q-GeO_2中次近Ge-Ge距离的电势系数＃alpha＃为9.57eV A〜（-2）。 r-GeO_2中第二和第三最近Ge-Ge距离的电势系数＃alpha＃分别为11.6和7.18eV A〜（-2）。有效的原子间电势在很大程度上受局部结构的影响，特别是受配位数的影响。通过使用势能系数＃alpha＃计算Ge-O和Ge-Ge运动的动力学矩阵，沿着[100]估计了q-GeO_2和r-GeO_2的声子色散关系。石英型结构具有更复杂的结构，在103和141meV之间具有宽的间隙，并且最高能量为149meV，而金红石型结构具有连续的分布并且最高能量为126meV。

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