Evidence for an I2/a to Imab phase transition in the silica polymorph moganite at ~570 K
Evidence for an I2/a to Imab phase transition in the silica polymorph moganite at ~570 K
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DOI：
10.2138/am-2001-11-1204
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发表时间：
2001-11
影响因子：
3.1
通讯作者：
P. Heaney;J. Post
中科院分区：
文献类型：
--
作者：
P. Heaney;J. Post
从100K到1354K的同步辐射X射线粉末衍射数据的Rietveld分析表明，在大约570K时，从I2/a空间群到IMAb发生了可逆相变，晶格参数的热膨胀行为在转变点处发生了剧烈的变化，单斜晶格的β角减小到90°。从α-到β-Moganite的位移转变受明显刚性的四面体绕[010]轴旋转的影响，体积应变和非对称破缺E11和e22应变的线性温度关系表明，转变的特征是二级的。在整个温度范围内，b轴的不断增加揭示了四面体在[100]附近的伴随旋转，这并不影响整体对称性。此外，我们还利用飞行时间中子衍射数据对α-MoGaNite在室温下的结构进行了修正。
Abstract Rietveld analysis of synchrotron X-ray powder diffraction data for the silica mineral moganite from 100 K to 1354 K has revealed a reversible phase transition from space group I2/a to Imab at approximately 570 K. The thermal expansion behavior of the lattice parameters alters sharply at the transition point, and the monoclinic β angle decreases to 90°. The displacive transition from α- to β-moganite is effected by the rotation of apparently rigid tetrahedra about the [010] axis, and the linear temperature dependence of the volume strain and of the non-symmetry-breaking e11 and e22 strains indicates that the character of the transition is second-order. The continuous increase in the b axis over the entire temperature range reveals a concomitant rotation of tetrahedra about [100] that does not affect the overall symmetry. In addition, we present a refinement without structural constraints for α-moganite at room temperature using time-of-flight neutron diffraction data.